e36 M3 - P0101 and it isn't a bad MAF

[salineco5]

Hi, thought I would mine the collective wisdom on here for this one before I go down the road of replacing the engine wiring harness...

Have had a P0101 code (MAF out of range). Code sets with key turning to start position (before car turns over). Car is rough at idle, dips down, under throttle is fine. Running rich. Must be running on it's fall back programming. Runs the same with/without the MAF plugged in.

So far:

- New MAF installed and known good MAF installed. Neither made a difference.
- 2 additional DMEs swapped in. Code still came back.
- ICV removed and cleaned. Valve moves freely.
- Traced wires as best as I could without removing the intake manifold. Pulled sub-harness for crankcase sensor, looked fine. (I had a mouse munching on wires problem before which required a new sub-harness).
- Cut open the sheath surrounding the 4 wires running to the MAF to ensure they were good.
- Testing the connector to the MAF I get 12.4V on one wire and 0.09 on the other (I'm guessing that is the variable signal? Seems low).
- All grounds were verified
- Didn't find any vacuum leaks (and since it is setting before the car is starting, I doubt it would be a vacuum leak).

Both the cam and crank sensors were replaced about 8 months before the onset of the issue. 2 days before the P0101 showed up I had an 02 sensor code come up (one of the upstream ones, don't remember the bank). I had cleared it successfully and 2 days later the P0101 came on. I replaced both upstream 02 sensors with new Bosch units and never saw the 02 sensor code again.

So, any thoughts on anything else I should consider at this point? Thanks for your consideration.

[thejlevie]

Since the code will set before the engine is started and since you have tried two other MAF's, I'd say the problem is either in the engine wiring harness or in the MAF input section of the DME. You should run continuity and ground tests on the MAF wires as a first diagnostic step. If that doesn't reveal a problem I'd be tempted to swap in a different DME before I swapped out the harness.

[bmwdirtracer]

+1 to every word.

Only thing I'd add is that before searching for a DME to swap in, I'd clean the plug of the dme (both sides), and open the dme to look for moisture or corrosion.
Use electrical contact cleaner or maf cleaner, and a toothbrush on any corrosion you see.

The code resetting before the engine starts is a sure sign: as long as you're sure the code is actually being cleared: since the clearing requires the ignition on, and it's an ignition-on fault, I might expect "Failure to clear code". I'd wonder whether you're using a "code-reader", with a paper chart, or a pro scanner. I personally don't trust the former to correctly define the code.

[salineco5]

When I wrote computer I should have said DME, sorry - I've corrected it in my original post. 2 other computers were installed and the code still came back. This was performed at a local shop. As they put it - it isn't the DME, it isn't the MAF, has to be something in between, so replace the harness. I don't doubt them on the harness replacement option, but not knowing the specifics of what might be going on is bugging me. Replacing the harness is a bit like cutting the whole arm off because your pinky is bleeding.

I'm using a handheld unit for checking the code and reseting. Starting from the check engine light showing (2 cycles of engine starting), I can look and see 2 codes in the system - one is the freeze frame data for the P0101, and the second is a pending P0101. If I press the erase button, cycle the key in the ignition but don't start the car, I get a pending P0101. What I am seeing code wise is the same thing the shop is seeing.

Another key piece of information I left out by mistake:
- While driving the car I have had several instances of the tach swinging down to zero or all the way up and stopping for awhile before settling back to the correct RPM indication. Purely a gauge needle change, the engine isn't stumbling. Has happened when I took a left hand corner really hard and when I went over some bumps.

The signal is taken from the crank sensor correct? Seems to point to a wiring issue, possibly something shorting out in the harness?

[RNeil]

My tach and other instruments occasionally to the same thing. I do not think it is related to your other problem.

[RNeil]

My tach and other instruments occasionally to the same thing. I do not think it is related to your other problem.

[Eric93se]

Hey Salineco5 can you update us on your problem.

[salineco5]

Hey Salineco5 can you update us on your problem.

sure, never did nail down exactly what it was. Ended up with yet another DME, a new MAF, and a new wiring harness. Took care of the issue. And the cluster issue was indeed a separate problem which was cured via cluster replacement.

[Eric93se]

Well I got a chineese MAFS and it did not fix the P0101 (MAFS) code. I got a full refund. Now ordered an OEM Siemens MAFS that has low mileage, should arrive soon.

I don't know the only thing I messed with was the MAFS so I can't see it beeing wiring or DME right now. I guess i will pull the DME and clean the board and connections if that doesn't work.

Thanks for updating us.

Actually just to note, I did test my original MAFS and it was indeed dead. I saw the pinouts to power it up and use a blow dryer to send air over the sensor and what voltage to expect from the MAFS in another thread. So fingers crossed the next MAFS cures this ailment.

[Eric93se]

So just to update, a new (used) MAFS solved my problem. Also to note, my original sensor was missing one of the thin film resistors so I guess my engine chewed on one of them. That resistor was missing before I cleaned it and it all went to hell, so I don't know. I think others should check their MAFS to see that there is a film at the begining and one at the end, there are metal tabs that are still in place if the thin film resistor disappeared.