I think that this forum is great. I've learned so much and enjoy the opportunity to help others.
I have a '95 S420 that isn't getting power to the hot wire on the MAF sensor. I have traced the probelm back to
the ECU; it doesn't put out the 3-5V on pin 37 to heat the wire on the MFS. I have tried tracing the problem within
the ECU by following the circuitry from the pin.

I'm getting really fed up with Mercedes. I spend too much time repairing the car. I use to love working on the car, but now it has become a chore. What are your thoughts?

Thanks.

SS

 

I HAVE SEEN THE HARNESS ON THESE MAF SENSORS TAKE OUT THE CONTROL UNITS ALL THE TIME. CUT THE WIRE HARNESS SHELDING ON THE HARNESS THAT GOES TO THE MAF SENSOR SEE IF THE INSULATION ON THE WIRES IS COMING OFF. NOW FOR THE CONTROL UNIT WERE YOU CHECKING FOR VOLTAGE WITH THE KEY OFF OR KEY ON YOU SHOULD ONLY GET VOLTAGE WHEN THE KEY IS ON.

 

remove the air cleaner where you can see the hot wire.

a/c off, start the engine and run at 2000rpm for 5 seconds. blip the throttle immediately by fully flooring the accelerator pedal and release...turn off the engine at the same time while releasing the pedal.

have somebody look at the hot wire. it will glow to orange color. it's a self cleaning function.

if it doesn't, then you got problem.

i assume you have checked the continuity of the wiring already.

if it;s on the control unit, the engine would be running in limp home mode. no effect with air mass sensor connected or not.

have you checked for broken circuit inside the ECU? i got no schematic diagram for that.