ABS problems. Might not be the wheel sensors


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.


Second post:
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.


I’ve had a weird ABS problem since the start of the 2020 season. If I start the car directly from off (ie no pause on the run position) or start moving as soon as the car is running I will get an ABS light once I hit about 10mph.

If I pause on run before going to start, and pause after starting before moving, then 90% of the time I can get no light.

If I get a light, I have to cycle the battery disconnect to clear it (which inconveniently I cannot do from the driver’s seat).

I’ve cleaned sensors, swapped the ABS ecu (1991 red label variety) with no change. I thought the ECU swap fixed it initially but the problem returned later in the day. I’m thinking of swapping the ABS pump next… not sure what else to try.



No way that’s the pump. I would reseat the relays on the pump, and reseat the cable on the pump. If that doesn’t fix it, I would replace the ABS computer again.

This assumes it’s a late model and therefore has no ABS relay behind the dash.


correct, 91=no relay