The ABS on my '98 Chevy pickup is engaging at the wrong time. Have you heard abut this problem?

Dear Car Talk

Dear Car Talk | Aug 01, 2002

Dear Tom and Ray:

My 1998 Chevrolet pickup seems to have a defect as far as the anti-lock brakes go. The system activates on dry pavement at a slow, gradual stop 75 percent of the time. I know of four other people in the same town who are experiencing the same problem, one of whom is a mechanic. When the dealerships have been approached, they claim to have no information about this. Also, I notice that just before the complete stop is made, it feels like the brakes aren't catching, and almost a releasing sensation is experienced. I have taken it in to a highly respected local mechanic for a thorough inspection, and he said that mechanically, the brakes are fine and there was no readout on the anti-lock-brake computer. He cleaned dust from the wheel sensors. He said another '98 has since come in and is doing the same thing, and there seems to be no remedy. Can you tell me what the problem is, if there have been other complaints and if there are any new recalls? -- John

TOM: Well, it's not a complaint we've heard before about Chevys with four-wheel ABS. And unfortunately, General Motors had nothing to offer us on how to fix it, either.

RAY: I have two guesses for you, John. But keep in mind that they are just that: guesses. In 1998, the Chevy pickup had four-wheel anti-lock brakes, but it had discs on the front wheels and drums on the rear wheels. And drum brakes are notoriously grabby.

TOM: You don't say where you live, John, but drum brakes get even grabbier when they're exposed to moisture. So if you live near the ocean or in a particularly wet climate, moisture could be causing your rear brakes to grab, which would kick in the ABS.

RAY: If this were the case, the problem would be worse after the truck sat for a while, especially overnight, and would get better the longer you drove it.

TOM: And since all of the complaints you're reporting to us are from your own town, there could be an environmental factor, like moisture, at work here.

RAY: Another possibility is that one of your ABS sensors is bad. You say that one of the mechanics checked for an ABS code in the computer, but the computer doesn't always pick up on every problem.

TOM: Here's how your mechanic should check the sensors. With the car up on the lift, hook up an oscilloscope to each sensor, one at a time. Then spin that wheel. The electronic signal from the ABS sensor should show up as a wave form on the oscilloscope. And if one of the wave forms looks different from the other three, that's your bad sensor.

RAY: If you continue to have no luck, you should go ahead and file a complaint with the National Highway Traffic Safety Administration, since this sounds like a safety issue to me.

TOM: You can do that from our Web site, the Car Talk section of, or by phone at (800) 424-9393. If NHTSA gets enough complaints about a single safety issue, it can open an investigation, which could lead to a recall. Good luck, John.

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