Cranks but doesnt start, ABS and AIRBAG lights turn on

[Cesconeto]

Hello, today something really strange happened to my 12/1994 325i coupe.

Short version:

Engine cranks, while cranking the ABS and AIRBAG lights come on, doesnt start, fuel pump relay not activating.

Long version:

I lifted to rear end of the car to replace the fuel filter, some hoses and the fuel level sender (under driver side rear seat).

After doing that I hotwired the fuel pump to an external 12v power supply to quickly refill the filter/fuel line.

Reconnected both level senders and fuel pump plugs, started the car (rear end still up), everything worked fine, no warning lights on dash.

While the car was running I decided to put it in 5th gear and let the rear wheels spin freely as I went under it to check for any weird noises, all fine (car ran for 15~20 minutes).

Noticed the ABS light was on, as expected by having the rear wheels spin while the front were stationary, turned off the engine and lowered the car to the ground.

About 3 hours later, got into the car and noticed the brake pedal needed pumping (I didnt do anything to the brakes), tried to crank it, the engine cranks but the ABS and AIRBAG lights come on while cranking, and there is no ignition.

Upon further investigation I noticed that the fuel pump relay was not activating, hotwired the pump to run continuously and tried to start the engine again: same result, ABS and AIRBAG light up while cranking, no ignition.

What I already tried:

Remove battery lead and let it sit for a while.

Check ABS relays and all the fuses


Im all out of ideas, any suggestion is appreciated.

Thx

[MazerRackham]

Crankshaft position sensor?

[drstuess]

Yeah sounds like crank sensor. Ohm it to make sure it's in spec

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[Cesconeto]

Turns out it was indeed the CPS sensor, measured it and it was dead. The ABS and AIRBAG light were there just to mess with my head.

Thx for the replies. =)

[drstuess]

Turns out it was indeed the CPS sensor, measured it and it was dead. The ABS and AIRBAG light were there just to mess with my head.

Thx for the replies. =)

Awesome. I think the ABS light and Airbag illuminate while cranking normally. In your case it just let's you know that the DME is sending a signal and not dead or not getting power.

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[JDStrickland]

There is no diagnostic value in the ABS and airbag lights until after the engine starts, and then the value is that there is a malfunction of the respective system.