How to Test M42 AFM?

[cslayman]

Hi All,

Sorry to bring up an old subject, but I'm having difficulty troubleshooting my '95ti M42 AFM. Sergey brought up the subject a while ago, but it didn't appear to be resolved.

According to page 130-14 of the Bentley's manual, the air flow potentiometer can be tested by measuring voltage across pin 1 and 2 and should change as air vane is moved. Like Sergey, I found the resistance to be constant at ~11kohm. I tested all other pin combinations and could not find a variable resistance. I checked another AFM I picked up from the junk yard and found the same constant reading.

I know the ohmmeter is working. I have no check engine light and the car is running fine (a tad on the rich side). So is Bentley's manual right and I have two bad AFMs and no CEL coming on? It would makes sense that both AFMs have broken potentiometers but that is a condition that is not checked by OBD-1.

Here is a link to a thread Sergey brought to Bentley's editor:
http://tech.bentleypublishers.com/me...ssageID=242088

I'd like to know if anyone has resolved this issue and found Bentley's to be correct on a good AFM.

Thanks,
Charlie
1995 318ti
Aug 11, 2013

[pdxmotorhead]

I believe you do the testing with the meter plugged in.. And the other accurate way to do it is output voltage not resistance..

Beyond that mine is still working...

Dave

[cslayman]

Hi Dave,

When you say your AFM is "still working", what test have you done? Or do you mean your car is running fine and there is no check engine light?

Thanks,
Charlie

[pdxmotorhead]

No check engine.. If its out of adjustment or failing it causes huge driveability problems quickly. At least on my car.. Mine is running fine. I carefully clean it about once a year..

Its the same as most other bosche trapdoor AFM units so what applies to volvos, vw's etc applies to this as well..

Dave