ABS fault, then limp mode
 

Happened at highway speed, not braking. DING DING ENGINE FAILSAFE PROG then seriously-reduced power and BRAKE ABS warning lights.

Pulled off, restarted, limp mode gone, BRAKE ABS lights on. Then SERVICE ENGINE SOON showed up to this party.

Somewhat irony, I was going to a pick-a-part lot... and when I was done there, the BRAKE ABS lights were off and did not return. The CEL stayed on.

When I got home I hooked up my Ancel BMW-specific code reader, which does not seem to be very specific.

Do these make any sense in relation to what happened?

76 DME/DDE does not fulfill torque request
E3 Fuel trim bank 1, permissible range exceeded
E4 Fuel trim bank 2, permissible range exceeded
D3 Idle speed control valve, mechanical fault
28 thermal sensor for oil level defect
OA AUC sensor (the what?)
59 Central-locking drive's door, open circuit (unrelated but present)

Car ran fine after restart. I cleared all codes, will drive it some more tomorrow. Engine run s smooth, no misses, idles fine.

ABS fault, then limp mode
 

The circumstances ans order fits with a failing voltage regulator on the alternator.

Monitor your voltages real-time with three hidden menu. Look for dips close to 12v it should never happen.

AUC is the "nose" that sniffs the air for petroleum and the HVAC uses to turn off outside air.

Obvs you've seen this before :thumbup: Thanks for the lead.

What is the "three hidden menu"? Outside of alligator-clippping a multimeter to it I'm not sure how to monitor the 12V output.

The AUC sensor thing doesn't seem to indicate a problem with the sniffer so I'm wondering why it's there, unless it's sensitive to voltage..

Everything is sensitive to voltage.

Google hidden menu for your model. Once you get in look for menu 7 I think for voltage. It will display real-time voltage in place of odometer.

This thing? https://www.fcpeuro.com/products/bmw...tor-f00m145360

Thx again, AW. Coming from a crashed and now-crushed Volvo 240, this thing is far more complex.

Figure out if your voltage is stable first

If not then the VR is usually to blame.

I rebuilt the VR on both wife and my E53 valeo alternator. You need to determine which you have

Test 09 UB: 13.7V pretty steady but I will keep it going next trip.

Any suggestions on how to ID the alternator OEM? A Bosch regulator is cheap, a Valeo one is not.

ABS fault, then limp mode
 

But the valeo has a $20 diy refurbish kit including the brushes and slip rings.

When the alternator starts to go, it will work fine at higher RPM and volts drop on coasting like to a red light. If there is any appreciable dip like half a volt the brushes are worn out.

Voltage stayed between 13.7 and 13.9 at all engine speeds.

When the ABS faults happened (twice now) it was at speed and I wasn’t looking at the voltage reading the second time.

Buddy has ISTA and will hook me up when I get back from this long trip. Hope the fuel trim errors aren’t indicative of anything harmful.

After voltage, steering angle or wheel speed sensor are most likely at fault but neither of those will set limp mode or even ses light.


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