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'04 Cavalier, 120K mi. We've had it for 6 years, driven every winter. Now, this winter, we occasionally get an ABS fault. This probably always occurs under slipping conditions. When it happens, the 'Low Trak' light also comes on. So, it would be a 'Yeah, so?' thing, except it didn't happen before, and, I don't see this winter's driving as any different than prior years.

Tires are not new, but more than legal; I would say tread is about 'normal' for us - so, again, not markedly different than prior years. I also swapped them (front <-> rear), which didn't change anything.

Suspension is OK, AFACT, though the rear struts are old. In any case, the fault doesn't correlate with bouncing or such.

Edit (OP): The ABS (always, I think) works normally, and doesn't fault, when the brakes are applied. The fault occurs when there's slip under torque. Even, pretty minimal torque. I don't know if it happens every time there's slip. It seems unlikely, but I can't rule it out.

Q: Why the change?

Bonus Q: Once a fault occurs, ABS is disabled until the car is shut off and restarted. Why would they design it that way? If ABS is safer, isn't this unnecessarily less safe?

Thanks

George
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2 Answers2

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It appears that as soon as the vehicle detects a wheel has locked up, the ABS goes into failure mode. This would suggest to me that you may have a fault in the abs module.

If it was a wheel bearing or sensor that was at fault, I would expect occasional false activation of the ABS and also normal activation where the pedal judders.

It looks instead like the ABS ECU is detecting the wheel locking, then it tries to activate the ABS, but either the ABS valve body or the possible the pump mechanism is not working correctly and so the ABS fails.

HandyHowie
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In my experience intermittent ABS issues are not solely but often caused by a worn wheel bearing. This is speculation but it may be that the spinning wheel is effecting the wheel bearing. The worn bearing allows the hub to move enough to miss a sensor pulse and light the fault light.

mikes
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