Come on folks. Anyone?Ok folks. re-awakening this thread.....
The strange ABS effects got gradually worse and became undriveable. And un-MOTable, if that's a word.
I replaced both front sensors and a cracked reluctor ring on the left front. Thought I'd solved it when I found the cracked reluctor. No difference.
I replaced the brake booster block with a used, but working unit. No difference. Could both have identical faults?
The warning lamps go out once moving, and when the 6.7Kmh ABS activation speed is exceeded, a continuous soft "chattering" noise can be heard from the direction of the brake booster.
Below this speed, the vehicle brakes perfectly. Above it, all sorts of weird effects appear.
The pedal is often "blocked" and requires considerable force to depress it. A hard banging can be felt through the pedal, and brake power as if un-assisted.
Oh, if I disconnect a wheel sensor to disable the ABS/TC, the vehicle brakes perfectly.
Clearly the ABS system doesn't think there is any fault, otherwise it would disable itself.
I've now got a nanocom.
Live data shows the minimum 1.7Kmh at all four wheels, and all increase steadily until about 6.7Kmh when the ABS comes on. The data freezes at this point.
Live data also shows 2.33V at all four wheel sensors until the chattering noise starts (6.7Kmh ABS on speed), at which point all the voltages go crazy.
Faults give "Left Rear sensor shorted to another sensor" which is obviously not possible, but is apparently a common indication of a faulty ECU.
Bought a used, but "tested" ECU.
Absolutely no difference whatsoever !?*?! Precisely the same symptoms.
Any bright ideas?
rgds Alan
Sorry, I wasn't clear.10 to 15 seconds is too short, from zero pressure it should run for 30-40 seconds. Maybe the hose has collapsed internally?
Hmmm, It would only need a full run if it leaked down overnight. I would have thought the system should hold pressure better than that.Not usually. If left standing overnight it'll usually run for the full time. If it runs after pressing the brake pedal, then there's something wrong. Does it kick in if the car is just left idling and the brakes aren't touched?
That's what I originally thought too, but the early modulators had a weak point which caused the same result, so I wondered if the later ones could have something similar?It seems very odd that you changed one brake modulator for another and still had the exact same fault, which suggests that isn't where the fault lies.
Yes, I tend to agree. It could hardly have failed gradually. Its a switch which is either off or on.Interesting theory. The brake light switch has two contacts, one is connected to the BeCM (to operate the brake lights), the cruise control ECU, the ABS ECU and the EAS ECU, while the other contact is connected solely to the ABS ECU on pin 14 on C0504. With the brake pedal pressed there should be 12V appearing at that pin.
Thinking about it though, if the switch had failed so only one contact was doing something, then the fault would just have suddenly appeared, rather than being there and progressively getting worse.