Laurence Gibbs

Fault: At start up , ABS light comes on along with gong and light stays on while all others go out. Previously the ABS light and gong came on for a short while and went out and all was well there after.
So far i have.....
tested R34 ABS relay. pin 30 supply to ABS brain 13v when engine running, pin 31 IS grounded less than 1 ohm. Pin 15 is 13v when engine running, pin 87 13v. I have also tried strapping out the relay just in case a h/r exisits. So i think the relay is all ok.
Pin 1 of the ABS brain is 13v when engine running connector un connected. All the solenoid valves read about 4 ohms at the ABS brain connector taken wrt to pin 20 gnd for solenoid valves. All wheel speed sensors read 1k ohm apprx.

I am making the assumption that the pin outs for the RS brain are exactly the same as a C2 ABS brain.

So not sure where to go from here? Any help , ideas welcome. Is the abs unit known to suffer h/r 's ?

boxsey911

I had an ABS fault because of a bad wheel sensor. However, if it's one of those the light and gong does not come on until you actually move off. As yours comes on straight away I think you can rule out a wheel sensor being the fault.

BTW I chased my tail a lot when trying to find the faulty speed sensor. It was only when I measured the resistances at the ABS controller plug that I managed to identify the sensor that was faulty. Previous measurements directly at the sensor plugs told me they were all OK.

Laurence Gibbs

Thanks Steve, yep i had come to that same conclusion. The wheels aren't moving and it's direct from start up. + the sensors all bell out ok. I think the unit self tests twice. Once at start up and then at 5kmh to check the wheel speed sensors. Actually there might be a clue in the fact that the light comes on and stays on. I suppose that might mean the unit isn't testing itself ?

boxsey911

The light and gong at start up usually points to the relay or control unit at fault. Many have solved the problem by just changing the relay. Some by changing the controller.

In the past I've had it go off if the ABS plug is not seated correctly. With mine I have to hold back the silver tab and press it home before letting go of the tab. i.e. I don't snap it in to place like it's really designed to. However, if you've not removed the plug I can't see that being the issue.

It might be worth removing the controller and cleaning up the pins to remove any of the green oxidation that builds up over time.

ras62

Relay 51 controls the booster pump, maybe check it and fuse 15 are ok. Also make sure the battery is ok and no low voltage are causing problems.

Laurence Gibbs

Boost pump works fine. Hydraulics light goes on at start up and turns off 20 - 30 on first start up . quicker on subsequent start up , fuse 15 ok (has to be for pump to run).
Not tried latching the brain connector in the way you describe steve, got to be worth a go.
Not sure why the double post sorry

ras62

Fluid level ok? Could be the ABS unit is faulty, either one of the relays or the pump. The relays should read 0.7-1.7 Ohms across the coil. You can run a 12v lead from the battery and connect to pin 9 on the ABS unit plug which should make the ABS motor run. I did this on my C2 and the ABS has worked ok ever since.

Laurence Gibbs

Thanks ras , not tried checking coil resistance will give that a go.

boxsey911

Another thing to look at is to check the tail lead for the ABS unit where it connects to the positive battery terminal. Maybe it needs cleaning/tightening up?

Laurence Gibbs

Ras
are you sure about your resistance readings for the coils? mine run about 50 ohms each reading from either the plug or directly from the back of the relays? I have 12v between pins 1 & 2 on the pump / valve block assy plug also. I assume you meant the coils on the abs unit , not R34.

Laurence Gibbs

Steve
i have looked around that area and can't see anything amiss , though it's difficult without removing the battery(being an RS i have a cut out switch). I am assuming it's that lead that supplies the brain and i know i have 12v at pin 1 of the brain connector plug. It's almost as if everything is working except for the bloomin light going out.

ras62

My apologies Lawrence, those figures are for the internal solenoid resistance and are measured across 1&4, 3&4, 5&4. The relay readings seem ok, I cant see them both being down. Did you take a lead to run the internal motor, 12v to pin 9 and you should hear it running. Once those checks have been done you can discount any issues with the ABS unit. Rob

Laurence Gibbs

Thanks Rob,
thought it was unlikely that both relays could be wrong. I did blip the motor. Though I don't think it proves anything as I don't think the brain tests the motor until the car is moving, so it's out of circuit? It did whir away fine. The solenoid valves i checked back at the controller (brain) they were all similar readings and around 4 ohms.
I have also checked the voltages at the relay bases and they are also ok 12v on 87 pin of both relays (i think it's that connection that is fed directly from the battery) At the mo it seems to be pointing at the controller , though i am very loathe to hook it out and take a look, as i really think it must be something else.

Laurence Gibbs

going to check at the plug on the abs unit , just to double check

Laurence Gibbs

just double checked. 1.3 ohms on all valves at the block and back to the connector on the controller. my 4 ohm reading was wrt the solenoid ground pint rather than the pins the solenoids return on. I might have a bit of a look at the ground pin. though i did meter between gnd and pin 34 (solenoid ground pin)and got below 1 ohm, so it's possibly internal resistance of controller cct ?
So abs block seems to be okay dokey?