ABS light does NOT come on! - Alfa Romeo Forum
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(Post Link) post #1 of 32 Old 28-11-14 Thread Starter
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ABS light does NOT come on!

Mentioned this in a previous thread but still can't get to the bottom of it!

My ABS light does not come on at all when the key is in the MAR position.

I have checked the indicator bulb and even swapped speedo binnacles over but still the light does not come on.

Even creating a fault by detaching one of the wheel sensor connectors does not cause it to come on.

However the brakes won't lock up on emergency braking so the system appears to be working.

Can only assume it's a wiring fault somewhere but where to look?

Any ideas anyone please?
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The ABS warning light is not a bulb, it is a LED in the instrument cluster.

The LED is connected to the switched 12V and pulled to ground at Connector A pin 18. See wiring diagram for instrument cluster.

The control is done by the ABS unit. I don't know if your car is a PH1 or PH2 so I have attache the wiring diagram for both.
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Last edited by Henrik_45; 28-11-14 at 12:06.
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Hope you get to the bottom of it. Some times a car can't lock its brakes up because they're so weak even if you stand on them hard. You should hear it working, but some cars have really quiet ABS operation.
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Quote:
Originally Posted by Henrik_45 View Post
The ABS warning light is not a bulb, it is a LED in the instrument cluster.

The LED is connected to the switched 12V and pulled to ground at Connector A pin 18. See wiring diagram for instrument cluster.

The control is done by the ABS unit. I don't know if your car is a PH1 or PH2 so I have attache the wiring diagram for both.
Thanks for the diagrams! It's a phase 1 and I meant to say LED not bulb - I did a diode check with a multimeter.

So if I apply 12 volts to pin connector 18 it should illuminate the bulb?

Last edited by Alfa_Awfulsod; 28-11-14 at 16:52.
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Hope you get to the bottom of it. Some times a car can't lock its brakes up because they're so weak even if you stand on them hard. You should hear it working, but some cars have really quiet ABS operation.
The brake pedal judders on hard braking which I'm guessing is the actuators working?
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Somethings happening. A resistance check in the led socket as you turn the ignition on should show a closed circuit, if not do the same check following the wire back through each connector until you get to the ECU pin. Hopefully digging around under the dash will restore continuity to the circuit. Last resort would be to put your own wire in, but I would shy away from that idea. Its most likely a miss crimped spade in there somewhere, or unlikely a failed board component(diode, dry joint) in the ABS ECU. Has the ECU got a dedicated earth path for the ABS light? Just be methodical and use your eyes!
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You can measure the voltage between Connector A pin 18 and chassis (ground).
To lite up the LED pin 18 should be pulled to ground (0V) else you should measure 12V or close to 12V when not lite up
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Originally Posted by Henrik_45 View Post
You can measure the voltage between Connector A pin 18 and chassis (ground).
To lite up the LED pin 18 should be pulled to ground (0V) else you should measure 12V or close to 12V when not lite up
My ABS unit only has 15 pins - it's a phase 1 car with the 001 ABS unit
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Its a one off fault that can be sorted, just a bit of an adventure I'm sure you can sort out. Make yourself some fine pointy probe tips and start looking for the coloured wire at the respective connections, theres only a couple by the looks of things! You are spoilt by having a wire diagram.
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Earth the contact on A18 at C10 the instrument cluster whilst the engines running, led for ABS should then illuminate.

Connector A is the white one lower left on the instruments.

Should be able to disconnect pull it forward and get a probe on the contact.

Good luck.
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Earth the contact on A18 at C10 the instrument cluster whilst the engines running, led for ABS should then illuminate.

Connector A is the white one lower left on the instruments.

Should be able to disconnect pull it forward and get a probe on the contact.

Good luck.
Managed to get the light to come on using a multimeter and help from forum member PKR so the fault appears to be within the ECU itself. At least the pump unit does'nt need changing!

Thanks for the advice guys!
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So are you going to look inside the ECU or do you think its worth checking the earth wire that comes out of the ECU?
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So are you going to look inside the ECU or do you think its worth checking the earth wire that comes out of the ECU?
Was going to strip the ECU but do you think a bad earth on the earth wire might be preventing the light from coming on?
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If you recall, I tested the resistance between ABS unit and car body. It was fine. That doesn't rule out an intermittent problem of course, but the fact that the ABS light came on when pin 1 was connected to the ABS unit body and that the ABS appears to function in a brake test is indicative that the earth isn't a problem.
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If you recall, I tested the resistance between ABS unit and car body. It was fine. That doesn't rule out an intermittent problem of course, but the fact that the ABS light came on when pin 1 was connected to the ABS unit body and that the ABS appears to function in a brake test is indicative that the earth isn't a problem.
That's what I thought but who knows with Alfa electrics! lol Was unable to strip the ECU down in situ inspite of removing the brake fluid reservoir and relay fuse box so will have to take it to Marco.

Air-bag light is back on again - after changing the headlight dip beam bulb!!! arrrrrrrrgh!
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Have you tried replacing the abs module with one of a working car?
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You'll learn where all the connectors are in time lol. Take the ECU out, if you're careful with the reservoir you won't have to bleed the brakes! Sounds like you have some damp issues with the electrics and earths, lots of electrical cleaner n copper grease, maybe crimp in some new earth terminals?
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Have you tried replacing the abs module with one of a working car?
Might come to that if I can't strip the ECU down!
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You'll learn where all the connectors are in time lol. Take the ECU out, if you're careful with the reservoir you won't have to bleed the brakes! Sounds like you have some damp issues with the electrics and earths, lots of electrical cleaner n copper grease, maybe crimp in some new earth terminals?
I was thinking more a gallon of petrol and a lighted match!!!
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Its hard to light this time of year! lol. Most ECU earths are near it! It may have its own earth and not share it with another system, most ECU's will have several earth wires.
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Just a update on the above, on investigation i've found pins 3 and 4 are incorrect on the phase 1 wiring diagram they should be transposed to be correct. signal LTB-WHT wire is on pin4, earth BLK wire is pin3 of the square ECU connector G272.

Alfa_Awfulsod Thanks for the original post, I hadn't even noticed my ABS had no warning light on startup.

New ABS module ECU sorted mine. Bought the 0 265 204 001 block and ECU off Ebay in Tokyo! only one i could find :-)

MOT next!!!
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Thanks, I got MOTs soon, more expence lol
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Thanks, I got MOTs soon, more expence lol
Mine too! Tried to strip down ECU but it's a sealed unit - will need a replacement ABS unit!

Rare as hen's teeth!
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Can't you bend the taps up and ply it apart, or is it molded into a block of resin? Ring around ECU repairers, some may take on the work FOC, but you may have to pay their postage rates? Not a shared part that could be reprogrammed for your car? Good luck with the hen's teeth, they aren't that rare!
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Change mot stations......... if the abs is working then get an auto electrician to sort out the led to go on and off.
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