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K40 Overload Protection Relay Repair
 
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Pelican Technical Article:

K40 Overload Protection Relay Repair

Tom Morr

Time:

1 hour1 hr

Tab:

$0 to $123

Talent:

**

Tools:

10mm wrench, socket, ratchet, nut driver, Phillips screwdriver, soldering iron, solder

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

Hopefully none

Hot Tip:

Use electrical contact cleaner on the plug terminals

Performance Gain:

Restored engine firing and smooth running

Complementary Modification:

Check the fan below the K40 and repair and replace if necessary

The notorious K40 overload protection unit is a well-known cause of starting, idling, and engine stumbling problems. This unit provides voltage to the control modules and electrical components, including the fuel pump, electric air pump, and horn. When the K40 malfunctions, these components don't get their required voltage.

Troubleshooting should obviously begin with any diagnostic trouble codes (DTCs), followed by checking for blown fuses. If those lead to dead-ends, the K40 is worth scrutinizing.

The K40 relay is located in the control module box, under the hood. In left-hand-drive R170 SLKs, this box is near the exhaust manifold. A heat shield and a blower motor keep the electronics in the box cool. A non-functioning blower can be a root cause. With the ignition switched on, this fan is audible, and airflow should be felt with the control module's cover removed.

Visual inspection of the K40 might reveal a correctable flaw. Spending a few minutes under the hood can save more than $100 by not having to replace the unit. And if the K40 is bad, at least you now know how to replace it yourself.

Always disconnect the ground strap on the battery before doing any electrical work.
Figure 1

Always disconnect the ground strap on the battery before doing any electrical work.

Remove the four screws that hold down the control module box's cover (green arrows), then lift off the cover.
Figure 2

Remove the four screws that hold down the control module box's cover (green arrows), then lift off the cover.

A brass clip (green arrow) keeps the K40 in place.
Figure 3

A brass clip (green arrow) keeps the K40 in place. Pressing it outward sets the K40 free.

Pull the plugs off the K40 and remove it from the car.
Figure 4

Pull the plugs off the K40 and remove it from the car.

A skinny flathead screwdriver can be used to pry the relay board out of the case.
Figure 5

A skinny flathead screwdriver can be used to pry the relay board out of the case.

Check the relay side of the board for obvious problems: charred or loose connections, etc.
Figure 6

Check the relay side of the board for obvious problems: charred or loose connections, etc.

Faulty solder connections are most common in the board's upper left corner.
Figure 7

Faulty solder connections are most common in the board's upper left corner. Hairline cracks that affect conductivity aren't always obvious. Use the most powerful magnifying glass available to closely scrutinize the solder joints.

This K40 is fine.
Figure 8

This K40 is fine. The soldering iron dramatizes how full functionality can sometimes be restored by re-soldering joints that have gone bad.

Electrical contact cleaner can also help the proper voltage get to the various accessories.
Figure 9

Electrical contact cleaner can also help the proper voltage get to the various accessories.

Terminals that affect drivability include the 12-volt main feed (red arrow), fuel pump load (yellow terminal), ground (blue arrow), and fuel pump relay (purple arrow).
Figure 10

Terminals that affect drivability include the 12-volt main feed (red arrow), fuel pump load (yellow terminal), ground (blue arrow), and fuel pump relay (purple arrow).

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Comments and Suggestions:
Jimmy Bonz Comments: got a 97Merc.320. Right Turn signal WON'T function.Left is Fine,Em.Flashers Work,all Bulbs checked and Good.Could Not hear relay Clicking at All for Right Signal???? HELP???
November 16, 2016
  Followup from the Pelican Staff: Check if the switch is activating the turn signal when it is on. I would grab a repair manual. It will have the wiring.

Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts
 
Aida Comments: I have a 1997 slk 230 and one of my fuses keeps burning out but I can't find the fuse box online. The dashboard lights come on when I turn the key but the car does not turn on.
November 9, 2016
  Followup from the Pelican Staff: Use your owner's manual to identify the fuses. if you don't have one, it should be available online.- Nick at Pelican Parts  
Mark Comments: Hi I have a 1999 SLK 230 I am having starting problems I turn the key to start the car all the dash lights come up but the engine will not turn over have checked the battery and its good for some reason the radiator fan starts running any advice on what might be the problem
November 2, 2016
  Followup from the Pelican Staff: is the starter getting the signal to turn on? Are there any fault codes stored? - Nick at Pelican Parts  
euroguy Comments: thanks nick for your quick answer, there is no codes ,and i will check next time for spark or the fuel system ,
October 15, 2016
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
 
Fiberjunkie Comments: 1999 E320 w210 4matic wagon dash key on function fine all dash lights. turn key to crank and one clunk no crank Start relay manually operated and cranks perfect but no ignition/run. Replaced EIS ESL and ECU matched set. no joy. checked every connection positive and negative, tried a K40 from running donor car still no joy! Stumped?!? whats the secret?
October 14, 2016
  Followup from the Pelican Staff: What fault codes are stored? Start may be blocked my immobilizer. - Nick at Pelican Parts  
Gern2469 Comments: Just bought a 99 clk430. Bad ignition. Changed eis now it works properly cranks like mad and gets fuel pressure but won't start. Replaced crank and cam sensor k40 fuse box and relay. Only pending code is p1580 throttle acuator. Would the p1580 cause no start. Haven't checked spark but would think if one coil was bad it would still fire just misfire. Please any info would help. Ps was thinking maybe anti theft playing a part because ignition was broken.
October 14, 2016
  Followup from the Pelican Staff: Throttle fault will not block engine from starting, unless code is for mechanically jammed / open.

Check spark, fuel injector pulse and (fuel pressure), volume, quality and engine compression. Once you figure out what is missing, it will be easier to diagnose. - Nick at Pelican Parts
 
euroguy Comments: hello again ,i have a 2000 slk230 car stall on middle of the road and after 5 or more minutes starts without problems ,when this happens there is light on dash but not cranks,could be the k40 relay causing this problem? by the way secondary air injection monitor does not get ready for smog.
October 13, 2016
  Followup from the Pelican Staff: Possibly. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose. - Nick at Pelican Parts  
SPIKE Comments: Sorry should have added I didnt start car for over a month and the battery died,prior to this car was runnig great!
Thanks
October 9, 2016
  Followup from the Pelican Staff: OK, got it. - Nick at Pelican Parts  
SPIKE Comments: Hi,My Right hand drive SLK 230 Convertable starts and the engine runs but no acceleration when pedal pressed and the engine runs unevenly,MAF removed and no change,any ideas??Thanks
October 9, 2016
  Followup from the Pelican Staff: Is the check engine light on? Sounds like an engine misfire. I would check spark, fuel and compression on all cylinders. If not misfire, look to see if the throttle is reacting correctly via TPS feedback when pressed.
- Nick at Pelican Parts
 
Rich67 Comments: Thanks for the reply. It ended up being the MAF sensor. Ordered a bosch one from auto zone $120 compared to the dealers $600. Runs like a dream NOW.

Now it threw a map sensor code so I need to check the vacuum lines.
August 5, 2016
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
 
Rich67 Comments: Hello everyone. First time mercedes owner

So I just bought a 99 slk230 sport 5 speed from a 80 year old lady. In excellent condition. She barely drove it to the grocery store aND back the 12 years she owned it.
It starts right up sounds great no hesitations or stumbles revs up nice and smooth and fast. Idles perfect.

So I picked it up and the one problem it has is
When you accelerate more then 1/4 to 1/2 or more throttle DOES NOT matter the rpms it acts as if it goes into limp mode and then no more acceleration like loss of power.let off the gas and go back to under 1/2 throttle drIves great. No jerking no shakes nothing. It does try to still accelerate but acts like something is holding back.
Theres no check engine light on.
I changed spark plugs the y had Bosch supers. They looked like maybe original. Coil boots looked great no arc burns. Rubber felt soft not brittle. Coil wires looked the same

I took the MAF sensor off and it looked great no dirt or oil on it. I Still cleaned it with some MAF spray cleaner.

Neither one changed anything.

While test driving this time . I put the pedal to the floor and it seemed like it was trying to accelerate but the check engine light started flashing. I hurried and scanned it and read missfire 1 missfire 3 and random shut the car off looked at all connections started it up engine light was off and hasn't came back on.
But I haven't floored it yet either.

I then checked the supercharger to confirm it is engaging and as soon as I rev the motor it locks in and stays locked until it goes back down to idle. And then releases

I drove 10 miles freeway and streets driving it home from purchasing and it drove smooth, and great no missfires or hesitations, no roughness nothing.. IF IF I kept it under 1/2 throttle.

No engine light nothing.

Thanks in advance. Really appreciate the help

August 1, 2016
  Followup from the Pelican Staff: Sounds like an engine misfire. I would check spark, fuel and compression on all cylinders. One of those items will be faulty. - Nick at Pelican Parts  
Darlene Comments: I just bought a 1998 SLK230 and it ran great for a day. When we went to start it last night all the lights come on, dash lights, windows work but it won't turn over. The battery is old so we switched out the battery. The batteries were dead on the remote so we switched out those. Still nothing. Any suggestions?
July 24, 2016
  Followup from the Pelican Staff: IF it won't crank the starter may be faulty. Voltage drop the battery cables, then check for the signal to the starter solenoid. - Nick at Pelican Parts  
Defender Comments: I have a UK RHD R170 SLK 230 with all the symptoms of a K40 relay fault engine cut out, LIM light on, fast engine fan but no engine crank. I took the K40 out and it had the same PCB issue as the one in your picture …solder joints on top LHS were burnt and the PCB discoloured. I took the PCB to a TV repair shop and they re-soldered the 3 insertions on the top LHS for £5, while I waited. Re-installed the K40 in the car ..and it runs perfectly. Interestingly, a top-end misfire and failure to kick-down on WOT now fixed too had been like that since I bought it 12 months ago. Just wanted to say THANK YOU for your website ..I wouldn't have got there without it!
June 27, 2016
  Followup from the Pelican Staff: Thanks for sharing your installation process and experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
 
Nuxbantu Comments: Hi Nick.Thanks for the detailed info, on checking the top left corner of the track I found 2 dry solder joint cracks. A pass with the iron and all is working as should be. Save a few quid on a replacement also..Thanks again
June 21, 2016
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
 
ChuckSLK320 Comments: I have a 2003 SLK 320, V-6 R170 6 speed. The car will crank fine for 3 or 4 days and then refuse to start. All the dash lights come on, but when you turn the key to the start position, nothing. Happens both when the car has been sitting and also being used. I replaced the clutch switch and used jumper cables to obtain another ground. When the car won't start the electric seat will not work either. Should I move on the K40 relay checked for bad soldier joint or some other problem. Could it also be the ignition switch?
June 16, 2016
  Followup from the Pelican Staff: I would check the signal to the starter. You if the signal is present when starting, the starter is faulty. - Nick at Pelican Parts  
paulo Comments:
all cilinders at 10,5:1 compression, sparks checked ok, coils ok, fuel and air filter new, fuel pressure ok, no check light or any other indication, timming tensor replaced, ..... can you give me a hint? after a short time trying, as the engine warms up it idles rougthly and if you try to rev it up it ratters from intake....
thanks in advance
April 21, 2016
  Followup from the Pelican Staff: That is not a compression test result, that is the engine compression spec.

Check engine compression. Spark and fuel injector pulse when cranking. I can't take a guess at a problem without some info as to what is going on with the engine. - Nick at Pelican Parts
 
paulo Comments: Hi. i have an 1997 r170 manual 200 kompressor that was has this issue:
when you turn the ignition on it revs snothly for about 4/5 secs, then it starts working like it had only 2 cylinders and shuts down.
i have the timing tensor replaced, fuel pump, fuel filter, key imibilizer checked, coils and plugs, seted the motor to point and it stood the same. it starts very smoothly and 5 secs after it starts working like it had only 2 cylinders and shuts down. i called the mb road assistence and they only said that when it started stalking it had ignition issues on cylinder 2 or 3 and other times on 1 and 2.
de you think it might be an issue with the k40 relay? thanks
April 17, 2016
  Followup from the Pelican Staff: Is the check engine light on? Sounds like an engine misfire. I would check spark, fuel and compression on all cylinders.


Relay doesn't make sense for a misfire. - Nick at Pelican Parts
 
crayzhawyn Comments: nick,
my k40 part number is 210 540 02 72 which has slight differences in pin locations and 2 less 15 amp fuses. I am getting fuel pump cycle and 50-56 PSI on the fuel rail. my question is; Does the K40 power the ECM/ECU K1 unit? When i had a diagnostic check on my Mercedes 96 E320 w210 M104.995 directly to the diagnostic connectorx11/40 the ECM/ECU was not one of the modules that showed up. Car turns wants to start but as mentioned fuel pressure is good but no pulse to a noid light on all injectors. I am stumped. FYI all new plugs and coil overs and boots were installed 2 1/2 months ago. Car stalled while overtaking going up hill then stalled, no restart. Changed crankshaft position sensor last week. didn't start after switch. disconnected battery to check fuel pressure and charge system when car restarted took for test run seemed fine , only unusual thing was my torque app would lose data feed intermittently. Next day I changed fuel pump and filter took for test and decided to test with same conditions as when stalled so i floored pedal and engine went completely off just like the first symptom. since then it has not restarted and battery is now depleted. Any help would be appreciated as I am un able to locate a matching ECM preprogrammed.
April 11, 2016
  Followup from the Pelican Staff: Do you have spark? if missing injector pulse, it can be a sensor input or a theft block. I don;t have wiring to look at for the relay you mentioned. - Nick at Pelican Parts  
Matx Comments: Hello, I own a SLK 230 year 1999.
Issue-1: the dashboard lights are on, stereo works but when I turn the key the engine is dead...no sounds at all that it wants to start.
Issue-2: Let's say I am driving in the city.. all of the sudden the car stops..then we go issue-1. Keep trying for awhile then it starts again.
my mechanic cannot find the fault .... would it be worth to replace the K40 anyways? or what other checks we can do? please help!!
April 10, 2016
  Followup from the Pelican Staff: I can't help without knowing what is missing from the system when you are trying to start it. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose.
- Nick at Pelican Parts
 
Jude Comments: Thank tou guys I love you guys for all. The dedicated work you the best help for foreign cars no others
April 7, 2016
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Jude Comments: Hello I have a 1999 slk the car cranks but won't start we recently replace the Sparks, coils , and fuel pump ... The car will only start on. Starter fluid and died I had a mechanic looked at it and he connected his battery on the fuel pump wind the car ran great but soon he takes the battery off it dies he said she the relay must not getting power to the pump because the car runs fine plus before all this car ran fine the we took a look at the relay it seems burn. On two joints but we unsure if it's the reason so I'm currently awaiting for a new k40 praying for the best
And idea to why the fuel pump not getting power And note the car at one point would blow this fuse every time we put it in the radio fuse but it stopped
April 6, 2016
  Followup from the Pelican Staff: Start with the relay. If faulty, it will not provide power to the fuel pump relay or fuel pump. - Nick at Pelican Parts  
Sweeters Comments: Hi I have a 1999 slk r170 which has developed a problem. Under acceleration it loses power but does not stall. It starts ok and appears to tick over normally. Any suggestions would be greatly appreciated.
April 3, 2016
  Followup from the Pelican Staff: Could be an issue with the fuel pump. I would perform a fuel delivery system test. Check fuel pressure, volume and quality.
- Nick at Pelican Parts
 
Mikey Comments: Horn not working, which fuse is it linked with? I cannot see it listed in any of the 3 fuses panel listings.
I checked the K40 and all looked good.
March 8, 2016
  Followup from the Pelican Staff: I don’t have that info.


I would grab a repair manual. It will have the wiring and fuse info.

Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts
 
Dgb Comments: Nick I have 2000 230 SLK and it runs great and than I can be running down interstate or just iddling and the car just stops than want do anything when I turn the key. If I go and tap on the K40 it will start a do just fine. I replace the K40 and it did OK for a while...what could it be causing it
February 21, 2016
  Followup from the Pelican Staff: Tapping on the relay may have been a coincidence. The options of possible causes are endless. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose. - Nick at Pelican Parts  
Mike Comments: Could this cause my radiator fan to only turn on when the heating in the car is set to full with the EC off, its spins very weekly and the heater blower in the car works great?

I have a brand new fan control module which was the culprit at first and now about a month later the radiator fan is acting up again as mentioned above.

Thank you,
Mike
February 18, 2016
  Followup from the Pelican Staff: Have you checked if the fan power, ground or control signal is incorrect when the problem is present? That info can point you in the right direction. - Nick at Pelican Parts  
Mysticfixit Comments: Dear Nick, I've got a 1999 SLK Auto. It keeps popping the 2Nd. 15 Amp. fuse from the firewall K40 . I've searched high and low for what these fuses protect. I've opened the K40 & it seams to be OK. Please help. I thank you in advance.
Steve
February 12, 2016
  Followup from the Pelican Staff: I don't have wiring to check what is on the circuit. if you can get and share the wiring I can help.

I would grab a repair manual. It will have the procedure, special tools and torque specs.

Give our parts specialists a call at 1-888-280-7799.


- Nick at Pelican Parts
 
DRIZZY Comments: THIS K40 DIAGRAM IS FOR THE OLDER K40 BOX CAN U OR DO U HAVE A DIADRAM OF THE 99 E430 DIAGRAM I NOT GETTING 12 VOLTS TO THE SIGNAL WIRE
February 7, 2016
  Followup from the Pelican Staff: I don’t have that info.


I would grab a repair manual. It will have it.

Give our parts specialists a call at 1-888-280-7799 - Nick at Pelican Parts
 
chippy Comments: Just an update K40 relay repaired and working. It was the fuel pump relay inside the k40. 12volts going to relay but not activated. On close inspection the coil wire was slightly darker in colour than the other coils, it had burnt out on the inner wires but just showed slight discolouration on outer surface of the coil wire. continuity test showed fault. Replaced the fuel pump relay and working OK, Thanks to your detailed guide
February 5, 2016
  Followup from the Pelican Staff: Thanks for the follow up. Thanks for sharing your experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
 
Iain Comments: Does the k40 relay have anything to do with the roof ?operation wndows go down then nothing, if fault with swithes will windows still go down or does everthing need to check out first which might mean pump.do you have picures of elec connections for checking micro switches for front hood as you can check switches on hood at boot connection thanks Iain
February 4, 2016
  Followup from the Pelican Staff: What model and year vehicle? - Nick at Pelican Parts  
chippy Comments: Hello, My SLK 230 year 1999. Checking the K40 relay as per your great info guide. There is power at K40 relay to Red and Purple terminal. No power to fuel pump teminal yellow. All the solder joints look good. I connected all the leads back and removed the cover on the k40 so I could see the relays working as the engine was cranked. The relay connected to the yellow did not work but when I pushed the relay contact with a tooth pick the engine fired into life. removed toothpick and the engine dies.Is this a faulty K40 relay or should I be looking at other issues. Many Thanks
February 3, 2016
  Followup from the Pelican Staff: I don't have the wiring for the vehicle, so I can't be too much help on specific wire and terminals. Unless you can share a wiring diagram.

The relay is not being activated. It may be the control for the relay. - Nick at Pelican Parts
 
olee Comments: no fire to relay wire on k40
January 26, 2016
  Followup from the Pelican Staff: Trace the source backward to find the open. Use a wiring diagram. - Nick at Pelican Parts  
Mac Comments: Hi, I have a 1998 SLK 230 R170 right hand drive. When I turn the key to start it I get all dash lights as normal but it is just "clicking and not turning over. I'm an engineer myself so I thought this could be the battery. Checked the battery and it was fine. I then thought it would be the starter motor sticking. When's and got a new starter motor and fitted it on the side of the road but the fault is still there. I've seen people comment about a K40 or a K56 relay could this be the issue. Thanks in advance:
January 23, 2016
  Followup from the Pelican Staff: It could be. However, if you have a click the starter is attempting to engage. Voltage drop test the battery cables. - Nick at Pelican Parts  
Tesla Comments: I Ha this problem, the car would just stop all the lights would go out and the car would not restart for about 20 minutes. looked at the K40 board and all the solder joints seemed ok. but it did it again so I really got peeved off. using a soldering iron I reflowed every joint on the board.
Have not had the problem since
January 16, 2016
  Followup from the Pelican Staff: Thanks for sharing your installation process and experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
 
Procam30 Comments: Thanks nick the dme is controlling the clutch on is not stuck , what its my problem what do I need to change , when the car is off no keys the clutch moves free turns by hand as soon I put the key on ignition turn the the key to position 2 engine off the clutch gets stuck , start the car the clutch it's turning never disengage
January 7, 2016
  Followup from the Pelican Staff: This could be normal for engine starting. There isn't room for guessing here. Using a Mercedes-Benz scan tool, monitor the actual and desired value for clutch control. Is it ON, what is the clutch state when the fault code is set? - Nick at Pelican Parts  
Gio36 Comments: I found out what was wrong!! Nicked wires going to the ECU and the SAM
January 5, 2016
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
 
Amer Comments: Hi Nick,
Our SLK 320/2001 is not starting! the fuel pump is not getting any power! the K40 seems to be ok with no burns or signs of damage including the fuses all good, but when starting the car the fuel pump relay is not getting activated! checking around on the net someone is saying that this problem might be caused by the fuel cut off switch but we are not able to locate the switch to check on it. can you please help with that.
thanks in advance
January 4, 2016
  Followup from the Pelican Staff: Before suspecting something other than the relay, does jumping the relay out allow the vehicle to start? Does the relay have power for the coil and pump? Is the DME activating the relay? - Nick at Pelican Parts  
Procam30 Comments: Hi nick I have a 1999 slk 230 , manual transmission have error code p1236 supercharger clutch it's always engaged read a couple of forums and dicen red the conector for the supercharger and the clutch stops spinning then that's mean the clutch is not seized or burnt , checked my k40 relay it looks good no burns or bad solders any idea what it could be and why I need to do what I need to change or diagnose thanks for your time
January 4, 2016
  Followup from the Pelican Staff: is the DME commanding the clutch on, or is it stuck on? Check the signal to the control with the key on and engine off, then with the engine running. - Nick at Pelican Parts  
Gio36A Comments: Hello Nick,
I really looking for a help here:So my clk 500 wont crank wont start:Battery is good!When i tried to bypass the start relay the car cranks but wont start,i replaced the relayno crank no start.
i find out that there is no voltage to the purple wire from k40 to the solenoid,so i bypass it as well same resultcranking no start.
Please if you are having any idea, light me up.
Thank you.
January 2, 2016
  Followup from the Pelican Staff: I can't help without knowing what is missing from the system when you are trying to start it. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose.
- Nick at Pelican Parts
 
muratti Comments: ...and if I cannot find the reason for the power problem, would it be safe to hook the fan to another swithed power supply inside the box with an additional fuse added to the circut? Thanks a lot. BR
November 26, 2015
  Followup from the Pelican Staff: Like mentioned earlier, sounds like the electrical unit you are pushing on is faulty. - Nick at Pelican Parts  
muratti Comments: Thank you Nick. I checked all the fuses. They are ok. Still no power to the fan. The car runs fine without problems. It is a 6 spd manual. Only when I push it hard, the left window stops working. Probably control unit is effected from exhaust heat. I need to solve the problem before the ecu is fried.
November 25, 2015
  Followup from the Pelican Staff: If physical pressure causes a change, the unit is faulty. - Nick at Pelican Parts  
muratti Comments: Hi Nick. I noticed that the ecu fan is not working. I checked with multimeter and there is no voltage on its cables when key is in pos 2 or the car is running. Fan is not seized and runs fine if you apply voltage outside the car. Is there a fuse related to this? Or can it be turned on/off through a menu when connected to a MB computer? Pls advice. Thank you
November 24, 2015
  Followup from the Pelican Staff: You didn't mention what vehicle you are working on. However, it should be fused, inside the E-box where the fan lives. Check for broken or corroded wires, as I have seen that in many MB models. - Nick at Pelican Parts  
gregg Comments: HI STAFF I HAVE 1999 SLK230 . when turning the key contact ON, it seems that dashboard lights are ON, and when getting the "bip" you turn the key to launch the starter but nothing happen, excepted that the cooler fan is activated, I wait a few minutes and the car starts . my horn dose not work could I be k40
November 24, 2015
  Followup from the Pelican Staff: It could be the relay. First confirm that the starter is not getting the start signal when the key is turned. Then trace that signal to the control side. You will find the loss of voltage. - Nick at Pelican Parts  
Bob Comments: Hi Nick. I had e check engine light and got a P1236 code. Checked my k40 relay but all was in good condition. After reading some more forum notes checked the turbo clutch and it was on all the time. I read the following in quotations and discovered that the clutch was OK but have a potential ECU problem. “If the clutch is constantly engaged, you can disconnect the 2 pin connector looks like a little barrel with 2 wires clipped to the engine and see if the clutch disengages. If this happens then you know the K40 is supplying power, the ECM is supplying ground or wire is grounding before the ECM and the clutch is not seized all in one shot.” Any suggestions on what to do next?
November 19, 2015
  Followup from the Pelican Staff: What vehicle are you working on? What did you do to confirm the turbo clutch is always on and how / where did you disconnect the control for it? - Nick at Pelican Parts  
Et209 Comments: Hi Nick. Thanks for the quick reply. No check lights. Plugs are new and so are the coils. Strange is everything is good in the morning and I parked for work but sluggish when I am heading out for lunch! May consider doing a compression test too. Thx.
September 22, 2015
  Followup from the Pelican Staff: Check the fuel system when the problem is present. Possible the pump is failing. - Nick at Pelican Parts  
Et209 Comments: Hi Nick, I have a 97 slk200. Car now runs fine in the morning but during the second part of the day and when engine is hot, it's sluggish and almost stalls when I lift off at the traffic light when I move from brake pedal to accelerator. Could this be a k40'issue, vacuum leak, throttle body? Any help is appreciated. I have changed fuel pump, cps, new coils and plugs, new MAF.
September 22, 2015
  Followup from the Pelican Staff: Could be a fuel delivery issue. Is the check engine light on? I would check spark, fuel and compression on all cylinders.
- Nick at Pelican Parts
 
Gritz Comments: When I check voltage in 40 amp fuse on the relay I get less than 3 volts

Does this mean a bad relay or power to relay broken Dow elsewhere
September 8, 2015
  Followup from the Pelican Staff: The relay may be the issue. Just confirm it has good power going to it. - Nick at Pelican Parts  
brabus Comments: Hi Nick.I just discoverd that when I start the car, it fires but it only revs when choked by hand at the inlet manifold but also refuses to idle.2there is also another component on my inlet manifold, held by 4 5mm allen bolts.checking current on this part reveals that there is no current flowing to it.could it be the cause? and what causes it to rev when chocked only? the red/green lights go when its revving.cant find anyone with a scanner tool since I stay in a remote place. :-
August 25, 2015
  Followup from the Pelican Staff: is the mass air flow connected? Are all the intake ducts sealed? - Nick at Pelican Parts  
Walkrune Comments: To be more concrete, symptoms include:
- when turning the key contact ON, it seems that dashboard lights are ON, and when getting the "bip" you turn the key to launch the starter but nothing happen, excepted that the cooler fan is activated. To note that the starter work correctly when launching manually, but engine doesn’t start.
Feedback of forums advises me to check K40 relay
What is your feeling on this problem? Your help will be welcome.
Thank you in advance
BR
August 23, 2015
  Followup from the Pelican Staff: The issue could be in the ignition switch or a control module. Get a wiring diagram and trace the starter solenoid signal from the ignition switch tot he starter. - Nick at Pelican Parts  
Walkrune Comments: Tanks a lot Nick. My 230 SLK is of 2001, automatic gearbox series. When you said that "the main relay module is activated...... air pump": this means that all 5 relays must be ON?
Best regards
August 23, 2015
  Followup from the Pelican Staff: Those are the relays that turn on when starting, according to wiring. - Nick at Pelican Parts  
Brabus Comments: Thanks a lot Nick.the mechanic checked everything and gave it a thumbs up.but still it cranks and fires after like 5turns, the revs go up to 2000rpm then suddenly it dies, like it does when one turns the ignition off then the red and green lights start flashing for some seconds,10secs or so then they go off.the mechanic says the immobiliser has armed but it has never had this problem.is it possible to remove this system.please help.
August 20, 2015
  Followup from the Pelican Staff: No, you can't remove immobilizer. There should be a code stored for start blocked by theft. Can you have the vehicle scanned for codes? - Nick at Pelican Parts  
Walkrune Comments: It seams that the problem on my SLK 230 comes from K40 relay. Nevertheless i would like to know which relays are ON when at the start?

Thank you in advance
August 17, 2015
  Followup from the Pelican Staff: I guessed at what year your car was for this info I am sharing. Take that into consideration when testing.

The main relay module is activated, fuel pump, motor 87, traction, systems, horn and air pump. - Nick at Pelican Parts
 
Brabus Comments: Hi.I have a problem with my mercedes 2001 w210 E320 petrol with the m104 engine.it had transmission problems and I bought a new tranny.so now the car starts and then dies right away.also the rear view mirror red and green lights start flashing.it didn't have this problem before the tranny was replaced.what could be the cause.your help would be greatly appreciated.
August 7, 2015
  Followup from the Pelican Staff: I can't help without knowing what is missing from the system when you are trying to start it. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose.
- Nick at Pelican Parts
 

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