I was stopping for a light and my brakes only half worked, why?

Question

I have a 2002 Saturn L200 which I bought at 91,000 miles and currently has 106,000 miles. I replaced the rear brakes myself (with the aid of a mechanic) at about 98,000 miles. Up until today, I've never had any brake issues. Today the road was wet from rain but the rain at the time of the incident was light. I was braking at a light probably from a speed of about 15 to 20 mph. I had been driving that day for only about 5 or 10 minutes and but this wasn't the first time I used the brakes during that time. I can't remember if this happened as soon as I put my foot on the brakes but certainly at some point, I felt resistance in the pedal and I couldn't push the pedal all the way down. I also felt a vibration in the pedal and I think I heard a groaning sound. The car slowed a bit but was still moving towards a car stopped in front so I had to change lanes real quick to avoid crashing. I then pulled off the road and practiced braking in a parking lot but couldn't reproduce the issue, the brakes were working fine again. During a turn a couple minutes later I did feel a weird sensation in the wheel and saw the Low Traction warning light turn on for the first time since I owned the car. So I'm a bit afraid to drive the car now as I'm not sure what's going on. I know brakes and traction are worsened in the rain, but I've driven many miles in the car in much worse rain and never had this issue. Any advice would be much appreciated.

Answer 1

What you are describing sounds like the anti-locking brake system (ABS) was operating due to low traction with the road.

This may have occurred due to a combination of the following reasons -

• Wet road (especially following a dry period)
• Oil or diesel on the road
• Travelling too fast for the conditions
• Low tread on tires
• Braking too hard

The vibrating feeling will have been the ABS pulsing the brakes attempting to keep traction. It is likely that without the ABS, you would have totally lost control of the vehicle and would not have been able to steer into another lane.

Contaminants like oil and diesel can build up on a road surface during a dry period, then become dangerous when wet, so special care should be taken in these conditions.

Have you checked your tires that they have sufficient tread and are in generally good condition, for example, the rubber is not hard and cracked?

There is a chance that you have a faulty ABS sensor that only fails in certain conditions, but I would have expected the computer to have detected that and illuminate an error lamp.

I would however recommend that you get the computer error codes read to check that no errors have been detected. It would also be a good idea to get the brakes all checked just to be on the safe side.

Answer 2

HandyHowie's answer is certainly correct in all its detail, but I'd like to mention one more possible cause for the ABS activation.

Your wheel speed sensors contain magnets, and those magnets can attract and hold onto particles of metal or rust from your brakes, rotors and undercarriage. If there's too much buildup -- the face of the sensor near the tone ring would look fuzzy with particles -- then the signal produced by the sensor would be weakened. If the signal falls below a certain threshold, the ABS module will falsely sense that the wheel is not rotating, which normally would mean that it's locked up and skidding. This activates the ABS.

This issue occurs especially at low speed when the wheel speed sensor signal is naturally reduced. The remedy is to blow out the gap between the wheel speed sensor and the tone ring with compressed air.

I live in the rust belt, and I have a car with this issue. As long as I keep the sensors cleaned of particles, they work fine. Otherwise, I get occasional ABS activation at low speeds just before I stop.