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Pelican Technical Article:

Crankshaft Position Sensor Removal

Kerry Jonsson

Talent:

*

Tools:

Diagonal cutting pliers, 4mm Allen head socket with ratchet and flexible extensions

Applicable Models:

Mercedes-Benz R129 (1990-02)

Parts Required:

Crankshaft position sensor

Hot Tip:

Make sure the Allen bit is fully seated in the fastener so it is less likely to strip

Performance Gain:

Repair no-start condition due to no spark from a bad crankshaft position sensor

Your single crankshaft position sensor is the most important part of your electronic fuel injection system. It is the one sensor that tells the ignition module and/or the fuel injection control unit that the car is running and when it should trigger the two individual coils. There are two ignition coils, one for each bank of cylinders. Without this sensor input going into the ignition module the engine would not start and stay running. In this tech article we are going to go over all the steps to test and remove your crankshaft position sensor.

Here we are at the back of the engine on the top left side of the transmission bell-housing.
Figure 1

Here we are at the back of the engine on the top left side of the transmission bell-housing. Locate the crankshaft position sensor cover (green arrow). Remove the cover by popping it off. You should not need to use a plastic prying tool but you can if you would like. This picture illustrates the engine out of the car for photographic purposes.

Remove the single 5mm Allen head screw that mounts the sensor to the bell-housing bracket.
Figure 2

Remove the single 5mm Allen head screw that mounts the sensor to the bell-housing bracket.

Twist the sensor first then pull the sensor out of the bell-housing.
Figure 3

Twist the sensor first then pull the sensor out of the bell-housing.

Follow the sensor wiring harness out of the bell-housing area out the ignition module on the left side inner fender.
Figure 4

Follow the sensor wiring harness out of the bell-housing area out the ignition module on the left side inner fender. Pull up on the crankshaft sensor electrical connector to unplug it from the module. Look at how the harness is routed for installation.

The sensor is wired like a coaxial cable.
Figure 5

The sensor is wired like a coaxial cable. This means the center terminal is the signal and the outer ring is the ground. Measure the resistance between these two points and you should read approximately 750ohms. Installation is the reverse of the removal procedures. Route the harness of the sensor as it was routed before. Plug the sensor into the ignition module. Insert the sensor in its opening in the bell-housing. Install and tighten the mounting fastener. Install the crank sensor cover. Crank the engine and verify it starts.

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Comments and Suggestions:
John Comments: Yeh got it out, oil, a dremel, chisels and vice grips.. unfortunalty it didn't solve the problem.. ASR light on, now goes in limp mode.. everything on throttle body looks to be in great shape, wires ect..
July 18, 2017
  Followup from the Pelican Staff: Same faults as before? - Nick at Pelican Parts  
John J Comments: Well this was supposed to be a simple 10 min job.. my 129 is being a royal pos.. been trying to get the sensor out going on the second day now.. it will not slide out.. can twist it in both directions but will not pull free.. Abosolutely redick..
July 15, 2017
  Followup from the Pelican Staff: Just the symptom of an old engine. Try cleaning the surrounding area, then spraying penetrating oil. I bet corrosion is holding it in. - Nick at Pelican Parts  
JT Comments: This is probably a dumb question but I'm new to this - is the crankshaft position sensor the same as a camshaft position sensor? I have a 1995 sl500 v8.... thanks!
June 19, 2017
  Followup from the Pelican Staff: No. Crankshaft measures crankshaft position. Camshaft measures camshaft position. - Nick at Pelican Parts  
John Comments: Nick:
My 1997 SL320 must be a different animal.........you have to access the crank sensor from the bottom........I wrestled with this problem for 2 days........every source stated that the crank sensor could be seen and replaced from topside ........I am still puzzled........I appreciate your help, John
October 20, 2016
  Followup from the Pelican Staff: Hmm. What is the engine code of your model? - Nick at Pelican Parts  
John Comments: Where is the location for the sensor on the 6-cylinder? .........specifically: a 1997 SL320 R129 6-cylinder

Do you access it from the bottom of the car? Or under the hood?
October 18, 2016
  Followup from the Pelican Staff: You can access it from the top, working at the transmission bell housing, just below the coolant reservoir. - Nick at Pelican Parts  
bigken Comments: Is the sensor in the same location for the V12 and Dose the sensor have to be removed for testing?
thank you,
September 9, 2016
  Followup from the Pelican Staff: It should be in a similar spot. You can test it when cranking the engine, look for voltage output or a waveform using a scope. - Nick at Pelican Parts  
TK Comments: Nick, is the sensor accessible from the top or do I have to go underneath?
June 11, 2016
  Followup from the Pelican Staff: You should be able to get it from the top. Working near the firewall. - Nick at Pelican Parts  
boatman Comments: thanks so much for this article! it worked perfectly and following the directions i successfully changed out the crank sensor!!! thank you
December 9, 2015
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Luis Comments: Do you sell the plastic cover for the Crank-shaft Sensor?
Thanks.
Lusi
November 6, 2014
  Followup from the Pelican Staff: We should be able to get it.

Give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need.
- Nick at Pelican Parts
 

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Page last updated: Sat 10/21/2017 02:30:37 AM