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Pelican Technical Article:

MAF Sensor Replacement

Tom Morr

Time:

1 hour1 hr

Tab:

$250

Talent:

*

Tools:

Flat head screw driver

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

New MAF

Hot Tip:

Do not use oiled air filters

Performance Gain:

Better mileage

Complementary Modification:

Replace air filter
The mass air flow sensor (MAF) is used to measure the amount and temperature of air that is entering the engine at any one time. The mass air flow 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 which 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. 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 like the catalytic converters.

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. You should carefully inspect all of your hoses, clamps and intake tubes for air leaks prior to replacing the sensor. 

The new MAF comes complete in the air body housing so you will have to remove the complete housing to replace it. 
Begin by locating the MAF sensor and housing.
Figure 1

Begin by locating the MAF sensor and housing. It is located on the left side of the engine below the radiator hose, in front of the power steering pump (red arrow). If you are having trouble finding it just follow the intake tube away from the throttle body.

Disconnect the wiring harness from the housing (red arrow).
Figure 2

Disconnect the wiring harness from the housing (red arrow).

There are two clips on the wiring harness that you squeeze together (red arrows) and pull the harness straight back from the housing.
Figure 3

There are two clips on the wiring harness that you squeeze together (red arrows) and pull the harness straight back from the housing.

Use a flathead screwdriver and loosen the hose clamp connecting the flexible hose to the top of the sensor housing (red arrow) and wiggle the hose off.
Figure 4

Use a flathead screwdriver and loosen the hose clamp connecting the flexible hose to the top of the sensor housing (red arrow) and wiggle the hose off.

Unclip the two spring clips connecting the lower section of the housing to the lower intake pipe (red arrows).
Figure 5

Unclip the two spring clips connecting the lower section of the housing to the lower intake pipe (red arrows).

Pull the housing up and out of the car.
Figure 6

Pull the housing up and out of the car. The sensor is actually protected inside the housing and as with a lot of modern cars you can only get the sensor and housing as one piece. If you are going to try and clean the sensor only use MAF sensor cleaner on it and never touch the actual sensor film with anything.

The MAF sensor is unidirectional and can only fit into the car in one direction.
Figure 7

The MAF sensor is unidirectional and can only fit into the car in one direction. There is also an arrow on the side of the housing (red arrow) showing which direction the air needs to flow. The arrow points towards the throttle body. Installation is the reverse of removal.

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Comments and Suggestions:
alan Comments: Could you possible give me some advise.
I own a Merc Benz slk r170. I need help diagnosing a problem. The car will not start and if it does it runs so rough, if you press the accelerator pedal it will begrudgingly rev up to about 2500 rpm but take your foot of the accelerator it will start to run rough them cut out. When you rev it there is a smell off unburnt fuel. Any help would be most helpful.
June 16, 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.
- Nick at Pelican Parts
 
Keith Comments: Did the space where the MAF have an O-ring attached?
May 21, 2015
  Followup from the Pelican Staff: The sensor does. The sensor housing fits tightly into the duct. Going by memory. - Nick at Pelican Parts  
Sevierhd Comments: I have a 1998 SLK with 120k and have cel with code p1519. I've replaced and checked the cam solenoid and it reads 8ohms, I checked the power to the solenoid wires and it reads 7 volts. I've checked and replaced dry rotted vacuum lines and rubber connectors. The MAS has been cleaned. Cleared the code and it came back after a few drives.

What would be my next step in finding the cause to this code and repair it?
Thanks for your help.
April 30, 2014
  Followup from the Pelican Staff: The code is for a camshaft actuator. I would check desired verse actual camshaft position. The actuator or solenoid that control the actuator may be faulty. - Nick at Pelican Parts  

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