The classic indicator that you’ve got a wheel sensor problem is that the ABS light doesn’t come on until the car moves. This is because, once you’re moving, the ABS computer will quickly realize that it’s not getting a signal from one of your wheels.
But in my case it turned out to be the computer.
I was looking for help on the R3VLimited page because “some” of those guys are total experts. First post:
Ok ABS gurus, lets see what you’ve got.
The normal sensor tests are not identifying what the problem is.
My ABS light is coming on when I move the car and then halt it. I’ve done this a couple dozen times today and the behavior is always exactly the same. I move the car 6’ and halt, light comes on. I move it 12’ and halt, light comes on. I let the car sit still for a few seconds or a minute, doesn’t matter. It’s movement and halt–light comes on.
So it’s the sensor, right?
I disconnected all sensors but one and the behavior was unchanged. I did this at all 4 corners, and just to be sure, I did it all 2 more times. There is no corner where if it alone is connected, the behavior goes away.
Then I checked each corner with a multimeter. The test point was the white round plug. Each tested at 1K Ohms, or there about, exactly as it should.
So the behavior acts like there is a problem at a sensor, but the sensor tests aren’t indicating which corner is the problem.
It all worked fine 2 months ago. Late model so no relay under dash.
For a while the ABS light went on sometimes as soon as I started the car, but reseating the relays and connector at the hydraulic pump seems to have fixed that.
I worked on it all afternoon and the problem turned out to be the computer.
Before I pulled the computer I did the “disconnect 3 of 4 sensors” test a 4th time just to make absolutely sure. Then I hooked the multimeter up to each sensor and spun the wheel. With the meter in AC mode I could see changing V and the freq of the sensor square wave.
At that point I was kinda hosed. I mean, hell, the symptoms said wheel sensors but I’d done every test known to man, so what the hell was I supposed to do next?
Then I pulled out the old ABS computer, reseated the cable and tried again. Fail. So I pulled the ABS computer apart and looked over the circuit board. Nothing interesting. Put it back in and it still failed. Symptoms unchanged.
I went up to the attic, found a spare ABS computer, installed it, moved the car a bit and HOLY SHIT, NO ABS LIGHT!
Just to make sure I wasn’t losing my mind, I put the old ABS computer in, and sure enough it failed.
Problem solved. My ABS computer died. Weird.