Hey folks,

Hoping someone can shed some light on a few problems I am having. 1994 Coupe Turbo with 14vt and 550 ECU. I have had this car 10 years and now the fun is really beginning.

First up, the ABS light has now come on, it is constant from the moment you turn the key. Error codes are 4-8 and 1-9 which related to low voltage and relay failure/voltage too low. Removed ABS cover and checked voltage to relays inside the Bosch ABS unit, all present and correct. I can only imagine any other voltage issue is beyond the unit relays and in the circuit board of the device.

Also, Interior lamp, dash clock and boot lamp not working either. Maybe related, electrical diagram does show these circuits being interwoven, relevant or not, I do not know. No power seems to even go to these items. Oil pressure light is also non active. Have checked various earth points and cleaned them up, if they needed it or not.

All fuses check out, replaced them anyway. Have also found the fuel pump is wired directly from the ignition by someone in the past.

Any suggestions, would be greatly appreciated. The ABS issue is the biggy as I cannot MOT without. Can live without the interior lights and stuff in the meantime, but mentioned incase it is relevant.

Cheers

Silly statements first.

Have you checked the wires from abs sensors back to see if any breaks or damage anywhere?

I have not as yet, purely based on having suffered sensor failure before and using the same diagnostic check, it pointed me to the problem the last time I had an ABS issue. As you can see from the codes below, none of these point towards a sensor or ring problem. If it did turn out to be a sensor, then I could only conclude that the diagnostic check as per the manual is a total waste of time

Relays or relay power supply - 1-9
Battery voltage too low - 4-8

I have checked the voltage to the relays inside the ABS module, and the battery is tip top.

OK, replaced the module/board of the overal ABS unit and it is now fixed.

The relays are soldered in, so my theory is that one is stuck. I had no way to safely remove them without butchering the original board, but I will butcher them now that I have it removed, just to confirm the problem and maybe help anyone who encounters it in the future. Will put some pictures up later on.

However I am still without interior lighting and such, which is a separate issue at this point.

Posting what you find will be very interesting to all owners with Bosch ABS

Knowing how much is fixable will be invaluable

The other items are all controlled by the MFU ( Multi-Function Unit) which is a small black box situated behind the under-dash fusebox.

I think there is a test routine to check it it's working ok but I'd have to have a butchers in the electrical fault finding manual to find that.... or just search this forum for MFU and see what comes up.

According to Haynes:
To start the MFU self-test sequence, press the heated rear window switch and turn on the ignition switch, then release the HRW switch.
The MFU should beep to indicate test mode is engaged.
Press the HRW switch again.
Operate each of the control switches, i.e. door switches, wiper switches, headlamp switch. A beep from the MFU indicates correct operation.
Press the HRW switch again.
The MFU activates each of its outputs in turn: HRW, front & rear wipers, courtesy lamp.
Switch ignition off to exit MFU diagnostic mode.

MFUs are quite inexpensive at the moment. I have found that the MFU YWC10004 can be replaced by YWC10003 in order to bestow courtesy light delay on a car not originally specified with it.

^^^^^^ ^^^^^^

Yeah I came across that check the other night but the dentist put me off doing any further work .

Anyway on the interior lighting front, I have everything sorted, thankfully it was some basic fault finding, earth problems and such, nothing too major. I didn't get to the interior clock to illuminate but I am not too concerned as I had picked that location for the IBC.

Alright, now the ABS...

I must have edited this twenty times now because I am worried someone will kill themselves with a bodged repair. However I can add something of use. GM Omega and Pug 106 (some models) use the same control board. If a good known complete unit cannot be sourced easily (or you simply don't want to remove and bleed your brakes again), This is a route you can take.

What Bosch system you got is it Bosch 5.0 or 5.3 on those?

I am entirely sure on that number, John. ABS2E is what I have been operating off from the manual.

0 265 208 044 is the Bosch number on the assembly.

I see that the 5.3 system has an auto bleed procedure, that would be handy if it is this type fitted. I have read about a scan tool for other makes of car, if this was universal to all the 5.3 units, could be really useful.