Wiring fix could put the brakes on ABS indicator glitch

by Jim KerrBackyard Mechanic . Jan 26 2018

Question: I have an interesting situation with my ABS indicator light on my 1997 Mazda B4000 SE truck with rear-wheel drive and an automatic transmission. Also, my wheel-speed sensor is located on my differential. I don’t see any front-wheel sensors. The symptoms are as follows:

Scenario 1: if I turn the ignition on without depressing the brake pedal first, the ABS indicator comes on, extinguishes, then comes back on and stays on until I turn the ignition off. It makes no difference if I depress the brake pedal while the indicator is on. It stays on until ignition shutoff, regardless.

Scenario 2: if I depress the brake pedal and keep it depressed, then turn on the ignition, the ABS indicator comes on, extinguishes and stays off. However, if I release the brake pedal, the indicator comes on after about three seconds and stays on until I shut off the ignition. During this time, it makes no difference if I depress and release the brake pedal even numerous times, the indicator stays on until ignition shutoff.

Any help you can offer on this situation would be greatly appreciated.

— Merv

Answer: Your Mazda B4000 was available with rear-wheel anti-lock brakes (ABS) or optional four-wheel ABS. If you cannot find any sensors for the front wheels, your truck would be equipped with the rear-wheel system only. This system acts more like a load-compensating system, allowing different braking force on the rear wheels as cargo load weights change. There is only one speed sensor used and it is located on the rear differential, as you have described.

When you turn the key on, the ABS computer goes through a system check. During the check, the ABS light will be on. After the check, the light goes off, but if there is a problem, the ABS light will come on again. During the check, the computer checks the resistance of the speed sensor, the resistance of the hydraulic unit solenoids, the brake switch operation and a hydraulic switch on the ABS hydraulic unit. The system compares the brake pedal switch and the ABS unit hydraulic switch and is programmed to not test the brake pedal switch until it is released. The ABS sensor signal will be tested when the vehicle starts to move, but the actual signal isn’t tested until then, only the resistance of the sensor.

From your description, I think there is a conflict between the signal from the ABS unit hydraulic switch and the brake pedal switch, because the problem only occurs when you have released the brake pedal. I have seen very few problems with the ABS unit hydraulic switch, but if there is, the hydraulic modulator needs to be replaced. You should check that wiring from the ABS hydraulic unit to the computer, which is mounted beside the hydraulic unit, is clean of corrosion and tightly connected, but I think the problem is likely with the brake pedal switch. You can test the brake pedal switch with a test light on the electrical terminals as you press the pedal slightly, but I predict that replacing the brake pedal switch will most likely correct your problem.

Question: In this recent cold weather, I have been having problems getting into my car. It is a 2008 Dodge Magnum and the doors will unlock, but I can’t pull them open. It looks like they are frozen shut. Usually I can get in one of the doors and crawl over the front seat to start the car. Once it is fully warm, the doors will open. What can I do to fix this?


Answer: It doesn’t take much moisture to freeze doors shut when the weather turns cold. The best way to prevent this is to remove as much moisture as possible from the door weatherstrips and then coat them with a silicone lubricant.

There are two types of silicone lubricant available: spray and cream. I use both types.

With the spray type, I hold a rag along the weatherstrip and then spray into the junction of the rag and weatherstrip as I move the rag along. This prevents the spray from getting on everything else.

With the cream type, put some on a rag and simply wipe it on. The silicone lubricant will prevent moisture from sticking to the weatherstrip and prolongs the life of the weatherstrip, as well.

Make this a yearly maintenance item in the fall and your doors shouldn’t freeze shut again.