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E30 ABS issue


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ABS issue. Fixing a buddy's 1988 car post crash repair in the LF, ABS worked before the crash. Only visible damage to ABS area was some pinched wires (not cut, insulation taped where insulation was compromised) and a pinched hard line which was replaced. Dash light comes on with key, does not go out after car is started (everything stationary so we are not talking about wheel sensors at all at this point). Under dash ABS Relay is passing voltage. Swapped ABS ECUs = no change. Swapped modulator/hydraulic pump (unknown condition from spare shell) = no change, swapped back to original ECU = no change. Swapped modulator onboard relays before swapping modulator = no change, swapping onboard relays after modulator swap= no change.  Out of ideas. What does peanut gallery say?  Any way to confirm an ABS ECU or modulator is good?  ETM & Bentley have little to say about ABS ECU or modulator, I'm not even sure they identify all of the wires.  I'm hoping someone has found a source that I'm not aware of, thanks in advance!

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Recheck the wiring anywhere near the impact.  It may have been pinched worse somewhere else.  It's possible to pinch and split the internal casing and cause a short or open with very minimal sign on the outside.

 

The computer will recognise a shorted or open sensor the moment it's powered up.

 

My wife drives a salvage title car, and I've worked on many prior salvage vehicles for myself and others.  Pinched ABS wires are extremely common, but often very difficult to trace.

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I would guess from the peanut gallery that you have a wiring issue. 

 

When you turn the key to KL15 the light should come on and stay on.  Once going to KL50 it should go off.  

If it comes back on immediately (as soon as you return to KL30) before the car moves, its a fault with the wiring or the ABS module or the ABS pump.  NOT a sensor.

As you have identified, the sensors only cause the light to return if the car is moving and the module sees wheel speed from some but not all the sensors

 

 

Also, you should note that main-production e30's came with two different versions of the Pump and two different versions of the ABS module.  These are not interchangeable to my knowledge, so you need to confirm that the pumps and modules you are using for interchange are compatible.

 

I would suggest ohming out each and every wire related to the ABS.  The ETM has the wire numbers for all the abs wires, so it should be possible without too much trouble.

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Real oem shows that later pump as superseding the older pump but spare pump I did use was from a later car, so being able to confirm your incompatibility statement would potentially be key.  Both ecu’s I’ve tested are the black label (and had the same part number) vs the red label abs ecus in the late model cars. 

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3 hours ago, SonsOfIrony said:

Recheck the wiring anywhere near the impact.  It may have been pinched worse somewhere else.  It's possible to pinch and split the internal casing and cause a short or open with very minimal sign on the outside.

 

The computer will recognise a shorted or open sensor the moment it's powered up.

 

My wife drives a salvage title car, and I've worked on many prior salvage vehicles for myself and others.  Pinched ABS wires are extremely common, but often very difficult to trace.

Is your advice E30 specific? I thouught the sensors on the e30 play no part until they are moving, at least was my current understanding.  The pinch that occurred was on the harness that feeds the pump as it’s located just behind the headlight. 

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10 hours ago, jlucas said:

Is your advice E30 specific? I thouught the sensors on the e30 play no part until they are moving, at least was my current understanding.  The pinch that occurred was on the harness that feeds the pump as it’s located just behind the headlight. 

 

Not E30 specific.  Just learned after working on too many wrecked cars never to rule out damaged wiring near an impact.  I did not say it had to be a sensor, just that in general, an ABS module will recognize a sensor with the wires shorted together.  Although the E30 being an antique at this point, it's possible the computer doesn't have any self test functionality beyond sensor worky/no-worky.

 

My advice stands.  If you found pinched wires and all you did was tape them up, that's your likely culprit.

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2 hours ago, Team Infiniti said:

Generically speaking, a open or short in any wheel speed sensor will pull a light.

 

@Huggy how does one go about pulling abs codes on a e30?

There are no ABS codes on an E30.  No publicly available software or hardware device exists for the E30 ABS module, and as far as I know no-one has ever been able to reprogram the ABS computer internally.

 

The only diagnostic tool is the ABS light.  

 

The good news is that if its a sensor, the light will go off after start and stay off as long as the car remains stationary.  As soon as its sensors give it wheel speed data and all 4 dont match, the light comes back on.  So you can determine which is the issue by unplugging all of them and plugging one back in.  If the car starts moving and the light STAYS off, the one plugged in is the issue.

Edited by Huggy
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I answered some of your questions on FB.

 

If you have an e30 wiring diagram then follow below steps. If you don't then let me know and I can send you a link and also give you the pin-outs.

Unplug the ECU plug and Ohm out each sensor. It should be 1100 ohms, I believe.

Next test I would do is test for AC volts on each wheel pin-out. Spin (you will have to do it fast as you by hand) each wheel independently and test if you get AC volts. Should be about 0.3 volts AC.

 

Unplug all sensors. Turn car on and can even start it if you want. If the light does not go out then you have a power/ECU issue.

 

It's really a simple system.

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Update: I tested every wire going to the ABS ECU, over voltage relay and hydraulic pump. Every communication/signal wire between the ECU and pump measures at just over 1 ohm resistance. Every point that you expect 12V has it, charge signal at ABS ECU shows >14v when running. Every ground has continuity. Every wheel sensor resistance measures between 975-1015 (not that it should matter when not moving).

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Well the ABS is now working. I wish I could say I knew exactly why.   A buddy came over yesterday and we went through all the troubleshooting again, checked every wire again.  At one point we got some flakey readings from the over voltage relay so we it was replaced with a fused jumper but the ABs still didn't start properly.   We also cycled the pump and solenoids manually but jumping the pins at the pump. Double checked again the relays on the pump (this is the pump I swapped in last weekend out of my '90 spare shell). Convinced the pump could not be the problem at this point, we sort off gave up on trouble shooting and decided to bleed the system since we were sure we wouldn't be changing pumps again.  After that we moved onto adjusting the pushrod between the pedal and the master cylinder (booster delete car for weight reduction) as there was too much stroke before pressure build. At that point we were ready to move to the next project and my buddy suggested checking it one more time and wouldn't you know... The light went out!  I even switched back to the original ABS computer and it still goes out normally after start up. So  you can see why I'm not 100% sure why.

Edited by jlucas
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