ABS questions

Sat Feb 17, 2007 12:35 pm

1) all my sensors are fine 965+ resistance,but if there is dirt etc on the bit of the sensor by the wheel will this cause problems

2) if my abs relay has blown will this stop ABS functioning all together?

3)Which on of the 2 ABS relays usually blows?

4)if not, is it likely to be my ABS computer

5) is a ABS pump packing in a common problem?

Thanks

Sat Feb 17, 2007 1:49 pm

1) clogged up toothed rings, metal fillings etc., can cause problems.
2) Of course it will!
3) The third one, found only on early cars. Lives near the ECU
4) It's electronic - it can fail, but doesn't usually.
5) No.
There's a diode shown in the circuit diagram of the ABS pump unit, but I think it actually lives in one of the relays. Failure of this diode would turn the light on.
If the light goes out when the engine starts, and comes on immediately you exceed 3 (?) MPH, then it's a sensor problem.

Sat Feb 17, 2007 1:51 pm

ok thanks brian

Sat Feb 17, 2007 1:55 pm

Brianmoooore wrote: 3) The third one, found only on early cars. Lives near the ECU
.

mine is a H plate so where would i find it? abs pump?

Sat Feb 17, 2007 2:17 pm

H plate won't have the third relay.

Sat Feb 17, 2007 2:19 pm

oh right so will it be both relays that are blown do you know?

Sat Feb 17, 2007 2:32 pm

Highly unlikely. Open them up, check the contacts, and the diode that is in one of them.
I've never had to deal with an ABS fault that wasn't due to a sensor in some way.

Sat Feb 17, 2007 2:56 pm

ok i will go and have a look. my relays are most likely hammered as my car has been jump started alot of times during my rebulid

Sat Feb 17, 2007 2:59 pm

It's only the relay that you don't have that is damaged by jump starts.

Sat Feb 17, 2007 3:03 pm

ahh right, thats handy to know. on my multimeter there are 5 ohms settings 2000k,200k,20k,2000, and 200. when testing my sensors i used setting 2000. would that be right?

Sat Nov 17, 2007 9:00 pm

Brian I have an 88 E30 M3 would this have the third relay? is it the one on top of the ecu near the steering column?

I have replaced both rear sensors as the were showing low voltage still does not work tried swapping the ecu but this had no effect - ecu was good and in a working abs car

any ideas?

Martin

Sat Nov 17, 2007 9:40 pm

texas2201 wrote:Brian I have an 88 E30 M3 would this have the third relay? is it the one on top of the ecu near the steering column?

I have replaced both rear sensors as the were showing low voltage still does not work tried swapping the ecu but this had no effect - ecu was good and in a working abs car

any ideas?

Martin

Your car would probably have the relay - it's a rectangular silver thing and it's located near the ABS ECU.
Since your car is LH drive, I can't comment on the exact location.

Sun Dec 23, 2007 3:57 pm

Opened up the relay and the very small fuse inside had blown - repaired it and put it all back and ABS now working again

Sun Dec 23, 2007 7:39 pm

texas2201 wrote:Opened up the relay and the very small fuse inside had blown - repaired it and put it all back and ABS now working again

The fuse that you have repaired is part of the excess voltage protection circuit, which is designed to protect the early type ABS ECU against voltage spikes or excess voltage on the 12 volts supply line.
Can you think of any reasons for a voltage spike? Any flickering of headlamps when the engine is running? Any jump starting of your car, or using it to jump start another car?
I hope the fuse you've used is of a similar rating to the original, or you could do serious damage if the protection circuit trips again.

Tue Dec 25, 2007 10:05 pm

Hi Brian

I had a faulty wire in the two speed electric fan which keep flattening the battery and meant i was jump starting the car quite a bit ubtil we tracked it down

we have put in a similar fuse - all seems OK now - although the light came back on once yesterday but went out and stayed out once I had restarted the car

Martin