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Mass Air Flow Sensor Replacement - Porsche 911 Carrera
 
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Pelican Technical Article:

Mass Air Flow Sensor Replacement - Porsche 911 Carrera

Time:

1 hour1 hr

Tab:

$300

Talent:

**

Tools:

Tamper-proof T20 Torx driver

Applicable Models:

Porsche 996 Carrera models (1999-05)
Porsche 997 Carrera models (2005-08)

Parts Required:

Mass airflow sensor (MAF)

Hot Tip:

Try cleaning the unit first

Performance Gain:

Smoother-running engine

Complementary Modification:

Replace air filter

The mass airflow sensor (MAF) is located inside the engine compartment and is used to measure the amount and temperature of air that is entering the engine at any one time. Older-style meters used on fuel injection systems in the 1980s measured air volumetric flow, which worked fine, but then you also needed a separate sensor to figure out how cold or dense the air was. The mass airflow sensor senses the total amount of air passing the sensor and allows the fuel injection system to adjust the fuel mixture to compensate for cold weather and/or high altitude conditions. The MAF also incorporates an internal intake air temperature sensor that measures the temperature of the intake air.

The first indicator that you might have a problem with the MAF is the presence of a check engine light (CEL) on your dashboard. The check engine lamp can be caused by a wide variety of problems with the engine--you need to read the codes from the computer to get a starting clue as to what the problem is (see Project 20 for details on reading the codes). It's perfectly safe to continue to drive the car while the CEL is on, as long as it is not flashing. However, the engine will not be operating at peak efficiency, and you will most likely experience a loss in power and a decrease in gas mileage as a result. It's best to get the problem taken care of relatively quickly, as running the engine in this condition can potentially cause damage to other components, such as the catalytic converters.

The computer will know if something is wrong with the MAF because it will compare the values being output by the sensor to "expected" values that it should be receiving. This common sense check by the computer helps diagnose problems with every component in the system. If the MAF becomes dirty and is falsely indicating to the engine that the car is receiving very little air while at full throttle, then the computer will most likely kick back an error code.

To gain more information about the problem, you can try disconnecting the sensor completely and take the car for a drive. If you take short drives (30 minutes or less) with the sensor disconnected, it shouldn't cause any major damage to your car. The engine management system (DME) will enter into a type of "limp mode" that will compensate for the missing MAF. If engine performance improves dramatically when disconnecting the MAF, then the problem quite likely lies with the MAF.

Vacuum leaks and other air leaks in the system can cause MAF sensor errors. If you have a crack or leak in your air intake downstream of the sensor, then the MAF will be sensing less air than the engine is actually receiving. If the clamp on the throttle body happens to come loose and fall off, then the MAF will indicate almost no air being sucked through the intake, yet the engine will be sucking air directly from the engine compartment into the throttle body. The bottom line is that you should carefully inspect all of your hoses, clamps, and intake tubes for air leaks prior to replacing the sensor (see Pelican Technical Article: Finding Vacuum Leaks on the Porsche 911 Carrera).

The MAF is located on the left side of the engine compartment, just behind the air filter (see Project 3 for access to the engine compartment). For some reason, Porsche made it unusually difficult to remove the MAF by securing it with a T20 tamper-proof Torx screw. You need the special tamper-proof Torx drivers, which are not typically found in everyone's toolbox, but usually can be purchased at a good local auto parts store. Although the holes on the MAF look symmetrical, they are not, and the unit can only be installed in one direction. See Figure 1 for a close-up of the MAF. Removal is easy once you have the tool. Simply remove both screws holding it in place and pull it out.

It's very important to keep the sensor clean. If the air cleaner isn't working too well, it could allow dust and debris to collect on the MAF. If you've had a problem with your air-oil separator, it could have contaminated the sensor as well. Oil sucked into the engine intake from a defective separator can easily find its way back to the intake tube. If you have had major engine problems (like our project car with the blown-up engine), then you may find a ruined MAF. On our donor car, the MAF was soaked in oil and coolant residue that had found its way all over the engine. If you have an aftermarket reusable air filter, beware of how much cleaning and filtering oil you use on it. Excess oil may get sucked into the intake and find its way onto the MAF. To keep your MAF healthy, I recommend changing or cleaning your air filter often (see Pelican Technical Article: Replacing Your Porsche Carrera Air Filter (996/997)).

If you are replacing your sensor, it is extremely important that you get the proper one for your car. There are two basic types, one for the cars that use a traditional throttle cable (1999 only) and one for cars with an E-gas electronic throttle (2000 and later). In addition, the later-style E-gas sensor has been updated at least twice as of this writing. Porsche updated the sensors in the Carrera in 2002 with the introduction of the 3.6 liter engine. Here is a chart that shows the differences between all of the sensors:

Porsche Part #

BOSCH Part #

Application

Notes

996.606.123.00

0-280-217-007

1999 996 Carrera 2 (2 wheel drive)

Sensor for use with cable throttle cars

996.606.124.00

0-280-218-009

1999-2001 996 Carrera 4 (4 wheel drive)

2000-2001 All 996 Carreras

2001-2005 996 Turbo

2002-2005 GT2

2005 996 Turbo S

Original sensor for E-gas cars

986.606.125.01

0-280-218-055

2006 Carreras

2002-2005 996 Carreras

2007-2008 997 Carreras

2002-2004 Carrera 4

2007-2008 Carrera 4

2002-2005 Carrera 4S

2007-2008 Carrera 4S

2005 Carrera S

2007-2008 Carrera S

2004-2005 GT3

2007-2008 Targa 4

2007-2008 Targa 4S

Latest updated sensor

997.606.125.00

0-280-218-192

2007-2009 997 Turbo

Shared with Cayenne

In general, if the old sensor your removing has is a 123.00 or 124.00 sensor, then you should replace it with a sensor with the same part number. If the old sensor you're removing ends in 125.01, then replace it with 986.606.125.01 (the latest version available).

After reinstallation, reset your check engine light (CEL) using your code reader (see Pelican Technical Article: Reading Porsche 911 Carrera Fuel Injection Fault Codes). You can also disconnect the battery for a short while to reset the lamp, but I don't really recommend this approach (see Pelican Technical Article: Reading Porsche 911 Carrera Fuel Injection Fault Codes). On 1999-2002 Carreras, you can disconnect the battery for more than 20 seconds, but less than 50 seconds, to clear the trouble codes without having to enter your code back into your radio. On pre-2003 cars, the computer's CEL memory is cleared after being disconnected for 20 seconds, but the radio code is needed after 50 seconds disconnected.

After you have replaced or cleaned the sensor and cleared the code, you need to go drive the car and see if the code returns. If the same error code appears, then the problem probably lies elsewhere. Most of the time when you have an error code indicating a problem with the mass airflow sensor, it is usually solved by the installation of a new sensor. However, the computer can become confused sometimes and give misleading error messages. Wire harness issues, DME problems, and secondary air injection equipment problems may all give false MAF error codes. At this point, it's best to dive into the factory manuals and start going through the laborious test procedures contained in there.

Shown here is the mass airflow sensor (MAF).
Figure 1

Shown here is the mass airflow sensor (MAF). The main sensor fits in a hole in the air intake right downstream of the air filter. The green O-ring seals the sensor to the intake tube (yellow arrow). If you're having trouble with your MAF, you can try to resurrect it by cleaning it. Lightly spray the areas shown with the blue arrow with electrical contact cleaner--the one that I recommend is CRC Mass Air Flow Sensor Cleaner. Spray it and then shake the sensor so that any dirt or debris is washed away. Don't touch any of the sensor elements with anything (like your finger or a brush), as this will damage them almost immediately. Let it dry completely prior to reinstallation.

You need a T20 tamper-proof Torx bit (inset lower left) to remove the mass airflow sensor from its home in the intake pipe (insert upper left, blue arrows).
Figure 2

You need a T20 tamper-proof Torx bit (inset lower left) to remove the mass airflow sensor from its home in the intake pipe (insert upper left, blue arrows). It's typically easier to pull the sensor out of the intake tube first, and then disconnect the electrical harness. Be sure not to touch any of the sensor elements that are exposed. Clean the entire housing area prior to installing your new sensor. Take note of the opening at the bottom of the sensor (green arrow). The new sensor must be oriented so that the opening faces the oncoming air going into the engine.

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Comments and Suggestions:
Paul Comments: Thanks. Just to follow up, I tested with plug inserted and probed the back of the plug with key on, engine off, and under cranking conditions. The only anomaly I could find voltage wise was the temperature at PIN 1, it stayed at 3v and read -40F on the OBD scanner. I tested another car and the MAF was giving me correct temp with key on. So I ordered a new MAF from Pelican, installed. Car started, idled and has been running great since. Thanks for the help!
November 20, 2016
  Followup from the Pelican Staff: Awesome. Thanks for the follow up. -40f is the default displayed value when the IAT sensor circuit is open. - Nick at Pelican Parts  
Paul Comments: I should clarify, those readings are of the plug pins with connector unplugged from sensor. I was checking to see if I was getting voltage and ground.
November 11, 2016
  Followup from the Pelican Staff: Ok, you should test plugged in so the circuit is in the normal state. - Nick at Pelican Parts  
Paul Comments: Oops, should've been a question mark after "bad sensor". I do not have the tools for that data, best I can do is DVM reading on pins when key on, engine off, and cranking.
November 11, 2016
  Followup from the Pelican Staff: I don't have the voltage specs. you would have to get known good values to compare them to. - Nick at Pelican Parts  
paul Comments: I have '99 996 C2 coupe. Engine will start but not idle with MAF plugged in. Fires right up but then dies. If I unplug the sensor it starts and idles no problem. Checked PIN voltages on plug with key on, engine off, getting 12v at PIN 2, Ground at 3, 5v at 1 and 4, NIL at 5.
Bad Sensor. All fuel pressures, delivery good.
November 10, 2016
  Followup from the Pelican Staff: What is GPS in dme data stream? key on engine off and when you try to start it? - Nick at Pelican Parts  
busted Knuckle Comments: Nick,
Can you provide 1996 993 MAF Sensor replacement instructions?
Thank you
April 25, 2016
  Followup from the Pelican Staff: The intake air housing and ducts have to be removed. Then the sensor can be accessed, it is located at the front of the intake manifold, near the firewall.

We don't currently have that tech article. If we get a chance to perform the procedure, we will be sure to document it.

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
 
bustedknuckle Comments: CEL coming on occasionally with P0104 error code.
I suspect dirty MAF Sensor. I'm using after market K&N oiled filter.
Can you provide this MAF Sensor removal/cleaning detail for 1996 993?
Thank you
April 18, 2016
  Followup from the Pelican Staff: You shouldn't clean that style of sensor. Only replace it if faulty. - Nick at Pelican Parts  
Pkp4911 Comments: I just finished 3.6 swap into a 03 986 s. Relied heavily on 101 book for the swap. Softronic did the ECU conversion. The original mass air flow sensor was would not allow the car to operate properly and assumed bad. Was replaced with a second identical Bosch unit that did not work either. A 3Rd unit was sourced all same cat # allowing the car to start and run. Once driving the car there was a off idle lean surge which cause the car to buck and hiccup confirming that the car was running in a lean condition. Per 101, the latest update is a 997 prefix on the mass airflow sen sor. Scott at Softronic claims that there are multiple MAF's for this combination. Can the largest 997 prefix be used on the 3.6 996?
February 1, 2016
  Followup from the Pelican Staff: I am not sure, I don't have experience with the swap. Give our parts specialists a call at 1-888-280-7799. They can help you find the right part.
- Nick at Pelican Parts
 
Jeff Comments: 2004 996TT X50, car hesitates at max boost in 3,4,5th gear; no issue with low boost or full boost 1 and 2nd gear; thinking Air Mass Sensor ? is the bremi sensor any good or go with Bosch ? Thanks
November 30, 2015
  Followup from the Pelican Staff: Stick with Bosch / factory. - Nick at Pelican Parts  
col Comments: Hello,
We have manual 996 C2 year 1998. The car stalls occasionally while in neutral ie at traffic lights. No error codes show and the MAF has been replaced. Someone suggestion we reset the fuel management system. Do you think this may stop the stalling or do you have other idesd?
Thanks
August 15, 2015
  Followup from the Pelican Staff: A reset won;t remedy a stall.

You need to see what is going away when the vehicle stalls, power, spark, fuel, etc. Once you have that info, I can offer more help.- Nick at Pelican Parts
 
Jan Comments: My 2004 911C4S has a rough idle that makes the car vibrate. Just a slight increase in RPM makes it smoothe out. I've changed spark plugs, fuel filter, air filter, cleaned the injectors and throttle body. Even replaced a worn out transmission mount. Runs great at speed but shakes when idling in stop and go traffic. Seems to worsen the longer I'm running the car at any one time. CEL is not on. Could this be an MAF problem even though I have no CEL alarm? What suggestions do you have?
July 8, 2015
  Followup from the Pelican Staff: I've noticed that a few of the 2002-2004 996's have a lumpy idle. It was the flywheel on a few of them, and an IMS retrofit to the LN IMS Solution on another handful of them that felt the issue was worthy of a couple thousand dollars. Most of the cars however lived happily ever after with the vibration. Another thought is to check the motor mounts. - Casey at Pelican Parts  
Don Comments: CEL light came on after driving maybe10.miles. The vehicle is a 2003 996 4S. Do you think that this could be the mass air flow sensor.
Thanks
Don
May 15, 2015
  Followup from the Pelican Staff: First thing is first...you need to read the codes in the engine computer (DME) Once we know that information then we can logically determine a plan of attack. Also check the fuel trim numbers RKAT, and FRA for both banks if the fault is fuel mixture related. - Casey at Pelican Parts  
Pats Comments: What's the name of the cable that is attached to the MAF? My 997.2 has an electrical cable that is slightly melted about six inches from the housing where the MAF is installed. I would like to replace the cable. Do you carry that?
May 5, 2015
  Followup from the Pelican Staff: Is it a wiring harness? Can you share a photo of it?

Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
6Flat Comments: in reply to "Why other than voltage is the sensor suspected for being faulty?": Nothing, the dealer only mentioned the voltage being out of spec as reason to justify replacement to avoid future problems. No CEL.

On the use of CRC cleaner: its use is actually recommended in the above text. But this HFM5 series Bosch MAF is indeed hot-film type.
April 7, 2015
  Followup from the Pelican Staff: I would wait until you have an issue before replacing the part.

I will check with CRC and see what they have to say about the cleaner. In my experience, working with pro mechanics, cleaner have damaged many hot film sensors. Cleaning helps hot wire types, where road debris would build on the sensor wire. - Nick at Pelican Parts
 
6Flat Comments: Thanks for the overview. Very useful.
In my case 996, 4 wheel drive, MY2003 I was told that the MAF should be replaced as the output voltage at 'engine not running' condition was 1.03V whereas the requirement is 1.02V max I might have not noted the actual voltages correctly!.
However, the CEL is off and afiak the car runs great.
They also told me I could drive on until the light comes on, but they recommended replacement.
Does this sound familiar? Can I measure this with a DVM some way or with Durametric?
I have the mentioned CRC cleaner; use it?
Does it justify replacement?
April 6, 2015
  Followup from the Pelican Staff: Do not clean the sensor, it can be damaged as it is hot film.

Why other than voltage is the sensor suspected for being faulty? - Nick at Pelican Parts
 
Franck Comments: Thank you for your quick answer ! By the way - my 996 has got only 2 pre-cat lambda sensors... No post-cat sensors at all. Is it a standard product for the year 1998?
Kind regards
Franck
November 12, 2014
  Followup from the Pelican Staff: Not in the US. - Nick at Pelican Parts  
Franck Comments: Hello,...from Paris

I need expert opinion about my fluctuation idle rpm - 996 C2 year 1998. A couple of day ago, my idle starts at 900 rpm then goes down, when the engine is almost warm, at 700 rpm - great - then goes up until 1200 rpm when the engine is fully warm...
I cleaned my MAF and Idle Control Valve but nothing happened!I'm looking for a brillant idea that could help me to troubleshoot
Many thanks
Best regards
Franck HAMON
November 10, 2014
  Followup from the Pelican Staff: Check the crankcase breather valve and the intake air boots for leaks. You could have unmetered air leak or a vacuum leak. - Nick at Pelican Parts  
archie Comments: had same sensor same part with same part number fault on vw golf £30.00 + vat - may be we should look around a bit when buying bosch parts - uk prices mind
thank you for item its another one stored ...
March 26, 2014
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
 

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