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Discussion Starter #1
I have a 2000 GC, the driver of which complains that the brake pedal is squishy and later the brake pedal is hard. Additionally, during normal braking, on dry pavement, the ABS unit fires up.

The vehicle has a new master cylinder, and I replaced front pads and rotors 2 months ago, prior to these complaints. I noticed nothing abnormal during post-repair vehicle test drive.

Two nights ago, the brakes were bled again (boy was it hot and sticky that night, and the mosquitoes should have given me a red cross donors card). The vehicle was test driven, and behaved normally.

Yesterday, there was a complaint of ABS going off almost every stop, but not every stop.

My working hypothesis is that one or more sensors for ABS are failing, and that is the cause of the frequent ABS activations. Additionally, I have not verified that the vacuum booser valve is free and clear. Since they are fairly inexpensive, I may simply replace.

How does one identify which ABS sensor may not be functioning right?

Additionally, the shop manual suggests it is impossible to bleed ABS without a DRB unit. Is that the case, or are there some practical workarounds.

Thanks in advance for any guidance.
 

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From the FSM...

Check the tone wheels for broken or missing teeth
Contact with the wheel speed sensor
Alignment of tone wheel to sensor
and sensor to tone wheel clearance

The sensors send a signal to the Antilock brake controller assembly.
Trouble codes are stored and can be read by a dealer with a DRB.
So, the only way I know to find out if a sensor is bad is to have a dealer read the codes.

Maybe someone else who does brake service knows a way. Possibly by checking it with a VOM or by raising the vehicle on a jack, connecting a VOM to the terminals and spinning the wheel to see if it generates an AC signal.

Also, you could have a rear proportioning valve problem FSM BRAKES 5-91
Rear ABS cycling can be caused by excessive rear brake pressure.

You essentially have to remove the proportioning valve and install a special test fitting to bypass the BP valve to see if it is defective.
Or try one form another vehicle.

Just some quick info I found. Maybe it will help a bit?
 
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