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Pelican Technical Article:

MAF Sensor Cleaning

Tom Morr

Time:

30 minutes30 mins

Tab:

$8

Talent:

**

Tools:

Flat blade screwdriver

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

MAF Sensor Cleaner

Hot Tip:

Make sure the sensor is completely dry before re-installing it

Performance Gain:

Sends accurate incoming air information to the ECU, optimizing air/fuel ratio: more power, better fuel economy

Complementary Modification:

Replace the air filter, clean the throttle body

In supercharged SLKs, the Mass Air Flow (MAF) sensor samples incoming air after it's left the charged air cooler en route to the throttle body. Over time, the MAF sensor's probe can become coated in gunk.

One common problem is caused by utilizing oil-impregnated aftermarket air filters. When servicing these reusable filters, people tend to apply too much oil and/or not let the oil soak in overnight before re-installing it in the car. Oil from the oversaturated air filter migrates to the MAF sensor, where it coats the probe. Also, trapped debris on the unit's screen can compromise airflow to the throttle body.

If the MAF sensor isn't functioning properly, the car's ECU (Engine Control Unit) can over-fuel the engine. When the engine runs rich (disproportionate amount of fuel to air), the exhaust gas temperature rises. In extreme cases, hot exhaust can cause the catalytic converter's internal honeycomb material to unbond from the converter's housing. When this happens, the converter is toast.

The most common Check Engine Diagnostic Trouble Code (DTC) caused by a MAF fault is P0056. When the engine throws this code, the knee-jerk temptation might be to replace the sensor. MAF sensor prices range from around $100 for a generic or remanufactured unit to nearly three times that much for a genuine Mercedes-Benz/Bosch model.

Whether cleaning or replacing it, the sensor has to be removed. (Please see our how-to on the two-clip/one-clamp procedure.) For about $8.00, it's worth giving the existing sensor a squirt-bath with Mass Air Flow Sensor Cleaner. This aerosol chemical is similar to electronic parts cleaner. It delicately cleans oil and grime off the probe and housing, potentially restoring sensor accuracy. The instructions on the can recommend cleaning the MAF sensor every time the air cleaner element is serviced or replaced.

MAF sensor removal is covered in a separate article.
Figure 1

MAF sensor removal is covered in a separate article. For around $8.00, SLK owners will likely want to attempt to clean a problematic MAF sensor before buying a replacement.

The cleaner instructions recommends spraying 12-15 squirts inside the sensor, being careful to not contact the probe with the cleaner's straw.
Figure 2

The cleaner instructions recommends spraying 12-15 squirts inside the sensor, being careful to not contact the probe with the cleaner's straw.

Also squirt the plug contacts and the mesh screen.
Figure 3

Also squirt the plug contacts and the mesh screen.

After cleaning, no visible oil or contaminants remain on the probe, screen, or housing's inner wall.
Figure 4

After cleaning, no visible oil or contaminants remain on the probe, screen, or housing's inner wall. The cleaner evaporates in a few minutes. Make sure that the MAF sensor is completely dry before re-installing it.

Even though the probe assembly is bolted to the housing, the entire MAF sensor is replaced as a unit if it's dead.
Figure 5

Even though the probe assembly is bolted to the housing, the entire MAF sensor is replaced as a unit if it's dead.

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Comments and Suggestions:
Brownie63 Comments: Hi changed and sensor OK for about 13 miles then emissions light came on any ideas thanks Ian
November 21, 2016
  Followup from the Pelican Staff: What is code? - Nick at Pelican Parts  
andy Comments: My m/Benz c200 kompressor accelerator is not functioning what should I do. When I start the engine and then I accelerate it does not pic
June 15, 2016
  Followup from the Pelican Staff: Could be an issue with the fuel pump or restricted exhaust. I would perform a fuel delivery system test. Check fuel pressure, volume and quality.
- Nick at Pelican Parts
 

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