ABS Warning Lamp

[Chimmychanga]

Hi again,

I have a facelift (1990) 325i and I have recently replaced the bulb on the ABS warning lamp to find that it is on.
The lamp is on when the key is in the first position, goes out while the engine starts and then stays on.

So far I have had a look at the two relays on top of the pump and taken the covers off. There doesn't seem to be any obvious faults on these. Any ideas where to go next? From what I have read on the wiki this is a sensor fault.

Thanks

[Brianmoooore]

The lamp is on when the key is in the first position, goes out while the engine starts and then stays on.

Comes back on immediately after the engine is started, or when you start moving?

[Chimmychanga]

immediately after the engine has started

[Brianmoooore]

There are two versions of ABS wiring fitted to E30s, and your car could have either. Remove the access panel above the glovebox and see if you have a small cigarette packet sized silver coloured relay present, which should be clipped to the top of the body coloured piece of metalwork that supports the glovebox latch.

[Chimmychanga]

No small cigarette packed sized coloured relay there, just the ABS ecu, wires and a small blue relay.

[Chimmychanga]

I've gone back to trying to get this sorted. Definately no relay above the abs ecu so it must be the later system. If I turn the key all the lights go on, turn to start the car then and the abs light goes out. As soon as the car starts the abs light comes back on.
According to the wiki this means its a sensor fault but that section is then blank. Any ideas?

[PG325]

Has this always been a problem or something that has developed?

If it was a sensor fault I would have thought the ABS light would go out after starting but only come back on once the car starts to move.

I understand the ABS light goes out once it receives a signal from the DME relay, perhaps your light is not receiving that signal.

I had exactly the same problem when I fitted a replacement engine loom, unfortunately the loom needed an extra cable from the DME relay to the C101 socket.

Search engine loom and ABS, that will help you id if you have the correct wiring.

[Chimmychanga]

I have only known about the fault since replacing the warning lamp bulb so not sure how long it's been an issue. The only thing I've done that I can think of that could affect the abs is changing a front wheel bearing

[Brianmoooore]

Jack the front wheels off of the ground, disconnect the white, round sensor plugs from their sockets on top of the inner wings, and connect an AC voltmeter across the pins that come from one of the sensors, then spin that wheel. Transfer the meter to the other side, and compare the two readings.

[Chimmychanga]

I've just done that now and they both look to read about 0.9v when the wheels are spinning fast, the drivers side seems to read generally a little higher but it's not the easiest thing to measure.

The drivers side is reading 1k ohm and the passengers 0.9k ohm

[Chimmychanga]

Just checked the rear two sensors which both read 0.9k ohm. From what I understand this indicates that the four sensors are all good. Any ideas what's next maybe I'll try and get hold of an ecu

[Chimmychanga]

I've just taken out the two relays under the abs cover on the pump and gone through the circuits with a multimeter. All seems to be as it should. 50-60 ohms on both coils. A 0.5 drop across the diode and no breaks in any wiring with all continuity as on the diagrams on the relays.
I thought it was worth a check

[PG325]

Have you checked that the front ABS sensors are on the correct sides?, they are handed!

[Chimmychanga]

Haven't checked, but have never touched them before this. How do you identify the side? Thanks

[PG325]

ABS plugs have part numbers on, ending 1 and 2, but if you haven't swapped them and it has been working it's not going to be that!

[Chimmychanga]

Definitely no abs judging by how the car locks up under heavy braking. Does anyone know if its worth checking connections to the ecu or have a diagram for it? Mot next week so it's a fail I guess