Brake pad warning - Central Informer shot ?
11-06-2011, 10:00 AM
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Brake pad warning - Central Informer shot ?
So my "!" and "brake pad wear light" lit up after starting the other day.
I've recently week working on the loom along the right hand side (UK) as I found a cable had shorted and melted some insulation of other cables in the loom along that side. Anyway, I bypassed the shorted wire and effectively isolated it from the loom and taped everything back up again - the wire was for the interior lights.
Back the brake pad warning now. First my pads are not worn down - they are probably about half worn at the moment so I studied the wiring diagram and realised that the pad warning circuit is a closed loop running from the Central Informer ecu round the car and back to the ecu.
I pulled the plugs from the ecu and tested continuity from the out/in connections on the ecu and got a complete loop circuit no problems. I even pulled a pad sensor plug at the wheel to confirm a break in the loop - behaved as expected - i.e. broke continuity.
Next I tested for a ground short on the pad sensor loop - didn't get one so the loop appears to be ok and not shorted to earth.
Next I ran two wires from the two ends of the loop right at the ecu connectors to effectively bypass the loop entirely - bridge wire from I/3 to II/9 (I think) still gpt the light on when the car starts.
I read that the brake fluid level can cause the light to come on too, so I checked fluid and switch and all seems good.
The only thing I think left is that the Central Informer ecu is bad on the pad sensor circuit.
Any other suggestions would be welcomed
you know how it is when you're chasing electrical gremlins
thanks
Lee
I've recently week working on the loom along the right hand side (UK) as I found a cable had shorted and melted some insulation of other cables in the loom along that side. Anyway, I bypassed the shorted wire and effectively isolated it from the loom and taped everything back up again - the wire was for the interior lights.
Back the brake pad warning now. First my pads are not worn down - they are probably about half worn at the moment so I studied the wiring diagram and realised that the pad warning circuit is a closed loop running from the Central Informer ecu round the car and back to the ecu.
I pulled the plugs from the ecu and tested continuity from the out/in connections on the ecu and got a complete loop circuit no problems. I even pulled a pad sensor plug at the wheel to confirm a break in the loop - behaved as expected - i.e. broke continuity.
Next I tested for a ground short on the pad sensor loop - didn't get one so the loop appears to be ok and not shorted to earth.
Next I ran two wires from the two ends of the loop right at the ecu connectors to effectively bypass the loop entirely - bridge wire from I/3 to II/9 (I think) still gpt the light on when the car starts.
I read that the brake fluid level can cause the light to come on too, so I checked fluid and switch and all seems good.
The only thing I think left is that the Central Informer ecu is bad on the pad sensor circuit.
Any other suggestions would be welcomed
you know how it is when you're chasing electrical gremlinsthanks
Lee
11-14-2011, 03:01 PM
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So I bought another central informer ECU and plugged it in - still had the light on 
The light came on after I'd been in the loop to fix the holed hvac pipe so it was time to get back in there to take a look. The only section of loom I had not unwrapped was an offshoot section from the main look which runs along the passenger compartment rear bulkhead and mainly contains wires for the ABS and brake were sensors - it joins into the two silicone shrouded cables that run out of the body down to the rear wheels.
You get to it by removing the rear parcel shelf and it's just tucked under a cardboard cover at the rear of the back seat carpets.
After unwrapping this section of loom it was obvious that someone had been in there before and I found the shorted wire that I had mostly removed continued along this section to a joiner to a larger wire. The shorted wire had no insulation left on it but when it had shorted it had melted adjacent wires shorting them to each other. It would appear that either one of more of the pad wear sensor wires were shorted with maybe another function on the central informer.
Long story short - with the wires delicately separated and insulated the correct function was restored and the informer light went out. Wrapped the loom all back up with Tesa cloth tape and it looks (and functions) good as new now.
All down to after market alarm installation I think.
It took some real head scratching to work this one out as basic continuity test were suggesting things were ok and only fully inspecting the passenger compartment look revealed the problem. I also printed the particular wiring diagram for the pad wear function A2 size (4 x A3) to make it easier to read
I'll add some photos shortly and I guess I'm just writing this for reference to help anyone out in the future.
Lee
The light came on after I'd been in the loop to fix the holed hvac pipe so it was time to get back in there to take a look. The only section of loom I had not unwrapped was an offshoot section from the main look which runs along the passenger compartment rear bulkhead and mainly contains wires for the ABS and brake were sensors - it joins into the two silicone shrouded cables that run out of the body down to the rear wheels.
You get to it by removing the rear parcel shelf and it's just tucked under a cardboard cover at the rear of the back seat carpets.
After unwrapping this section of loom it was obvious that someone had been in there before and I found the shorted wire that I had mostly removed continued along this section to a joiner to a larger wire. The shorted wire had no insulation left on it but when it had shorted it had melted adjacent wires shorting them to each other. It would appear that either one of more of the pad wear sensor wires were shorted with maybe another function on the central informer.
Long story short - with the wires delicately separated and insulated the correct function was restored and the informer light went out. Wrapped the loom all back up with Tesa cloth tape and it looks (and functions) good as new now.
All down to after market alarm installation I think.
It took some real head scratching to work this one out as basic continuity test were suggesting things were ok and only fully inspecting the passenger compartment look revealed the problem. I also printed the particular wiring diagram for the pad wear function A2 size (4 x A3) to make it easier to read
I'll add some photos shortly and I guess I'm just writing this for reference to help anyone out in the future.
Lee
11-14-2011, 09:24 PM
#3
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Well done!
The 'Central Informer' monitors and shapes a host of inputs ..... as someone might search for the 'CI', I'll add one more mildly related diagnostic that implicates the module directly.
My car had an inoperative gas gauge ( petrol in the UK
) when purchased. After checking the wiring from the tank top, and then pulling the sender unit from the tank and tenderly disassembling for cleaning [ it is an analogue type .... variable rheostat, namely a float with a shunt that contacts two long strands of nichrome wire in a ~30cm tube] .... no improvement. In this case, a swap of the CI module, located under the steering column in a LHD car, solved the problem.
The 'Central Informer' monitors and shapes a host of inputs ..... as someone might search for the 'CI', I'll add one more mildly related diagnostic that implicates the module directly.
My car had an inoperative gas gauge ( petrol in the UK
) when purchased. After checking the wiring from the tank top, and then pulling the sender unit from the tank and tenderly disassembling for cleaning [ it is an analogue type .... variable rheostat, namely a float with a shunt that contacts two long strands of nichrome wire in a ~30cm tube] .... no improvement. In this case, a swap of the CI module, located under the steering column in a LHD car, solved the problem.
11-16-2011, 07:04 AM
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Yes another useful story. At least now I have a spare CI ecu for the future Honestly I would start buying up a full set of spare ECU's for 993's as these are the things which are going to cause us problems.
Here are some pictures of my cooked wiring finally showing them all bound up again with new loom tape.
Lee
Honestly I would start buying up a full set of spare ECU's for 993's as these are the things which are going to cause us problems.Here are some pictures of my cooked wiring finally showing them all bound up again with new loom tape.
Lee
