I'm sure my issue is related to the ABS because the ABS light on about 70% of the time. Here are the symptoms:
When the ABS light is OFF with the car running: the brake pedal will pulse when I apply pressure to it. It feels most like somebody is tapping the back side of the pedal with a hammer. The frequency and intensity of the pulsing varies, but its sometimes very strong. It will even do this if the car is at rest with the engine running. Even worse, at the same time, it is as though the brake pedal gets so hard I can hardly push it and thus, the car will not stop quickly. I'd hate to be in a panic stop situation with the ABS light OFF.
When the ABS light is ON with the car running: everything behaves just as it should. Go figure.
Now, I followed completely jlevies guide to ABS testing here:
Troubleshooting the ABS system isn't very difficult. It is a stand alone
system that only gets input data from the brake light switch, wheel sensors and
system power. The parts of the system are the ABS module located next to the
steering column, the ABS relay mounted above the ABS module, the ABS unit in
the left front of the engine bay, and a wheel speed sensor at each wheel.
If the ABS light comes on with ignition, but doesn't go out when the engine
starts, a wiring problem, bad module, or bad ABS relay are the likely
candidates. A failed or weak alternator will also cause this because the
system voltage won't rise enough. There is a fusible link inside the ABS relay
that can be blown. The relay can be repaired, or better yet replaced.
If the ABS light comes on when you turn on the ignition, goes out when the
engine starts, and then comes back on before the car is moving the cause could
be a bad module, a bad ABS unit, or a wiring fault.
If the goes out after engine start and only comes one when the car is moving,
there's a problem with one (or more) of the sensors. The simple test to find
out which sensor(s) is the cause is to disconnect all but one of the sensors
and drive the car. If the light comes on, that sensor is sending a speed
signal to the ABS and is good. Repeat with each other sensor to find the
one(s) that don't cause the light to come on. Since the ABS module has no
speed input besides the wheel sensors, if only a bad sensor is connected the
module can't tell the car is moving and thus doesn't fault on missing speed
signals from the other wheels. Once a bad speed sensor is found, if a new
sensor still doesn't work, there could be a wiring fault in that circuit or a
bad input channel in the ABS unit.
I repeated the complete test cycle three times and each time, I was able to get the ABS light to come on for each individual wheel sensor with the other 3 unplugged... the only catch is that sometimes the light didn't come on immediately when I started driving.
Any suggestions or ideas? I know I could just throw parts at it, but it would be nice to have some direction.
Thanks!
When the ABS light is OFF with the car running: the brake pedal will pulse when I apply pressure to it. It feels most like somebody is tapping the back side of the pedal with a hammer. The frequency and intensity of the pulsing varies, but its sometimes very strong. It will even do this if the car is at rest with the engine running. Even worse, at the same time, it is as though the brake pedal gets so hard I can hardly push it and thus, the car will not stop quickly. I'd hate to be in a panic stop situation with the ABS light OFF.
When the ABS light is ON with the car running: everything behaves just as it should. Go figure.
Now, I followed completely jlevies guide to ABS testing here:
Troubleshooting the ABS system isn't very difficult. It is a stand alone
system that only gets input data from the brake light switch, wheel sensors and
system power. The parts of the system are the ABS module located next to the
steering column, the ABS relay mounted above the ABS module, the ABS unit in
the left front of the engine bay, and a wheel speed sensor at each wheel.
If the ABS light comes on with ignition, but doesn't go out when the engine
starts, a wiring problem, bad module, or bad ABS relay are the likely
candidates. A failed or weak alternator will also cause this because the
system voltage won't rise enough. There is a fusible link inside the ABS relay
that can be blown. The relay can be repaired, or better yet replaced.
If the ABS light comes on when you turn on the ignition, goes out when the
engine starts, and then comes back on before the car is moving the cause could
be a bad module, a bad ABS unit, or a wiring fault.
If the goes out after engine start and only comes one when the car is moving,
there's a problem with one (or more) of the sensors. The simple test to find
out which sensor(s) is the cause is to disconnect all but one of the sensors
and drive the car. If the light comes on, that sensor is sending a speed
signal to the ABS and is good. Repeat with each other sensor to find the
one(s) that don't cause the light to come on. Since the ABS module has no
speed input besides the wheel sensors, if only a bad sensor is connected the
module can't tell the car is moving and thus doesn't fault on missing speed
signals from the other wheels. Once a bad speed sensor is found, if a new
sensor still doesn't work, there could be a wiring fault in that circuit or a
bad input channel in the ABS unit.
I repeated the complete test cycle three times and each time, I was able to get the ABS light to come on for each individual wheel sensor with the other 3 unplugged... the only catch is that sometimes the light didn't come on immediately when I started driving.
Any suggestions or ideas? I know I could just throw parts at it, but it would be nice to have some direction.
Thanks!
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