2004 chevy trailblazer 4wd ls ext has a loud rattle in front end near right…
My wife’s car has had an abs light on since right after we bought it. I had the codes read. They said it was the wheel speed sensor. I changed out both wheels speed sensors and put brand new brake pads on the front and back as well as new calipers all the way around. She said she drove it today the light still on and it was raining. She was coming to a stop sign and hit the brakes. It made an awful noise and it didn’t want to come to a stop. I have replaced the master cylinder and I have bled the brakes. I have also sanded down all the ground leads and put them back on and sprayed with undercoating as stated. Someone told me it could be the EBCM what should I do or change?
The description of what your wife told you would indicate the ABS was functioning properly. When the roads are wet or icy the ABS motor will activate, making a groaning noise, this prevents the wheels from locking up. When the ABS is activated the light may illuminate temporally and generally goes back off. If the light is on continuously the ABS will not function.
If you want to make sure the ABS doesn’t come and go you can disable the function by removing the ABS fuse or relay. Doing so will allow the brakes to function like all the old cars used to without ABS. Learning to brake a little earlier will help slow the car and also cause your brake pads and rotors to last longer. You can drive the car this way as long as you like but the ABS light will remain on.
If you want to repair the ABS system the use of a scan tool will be required for individual testing of components.
Antilock Brake System (ABS) Warning light
With the Anti-Lock Brake System (ABS), this light will come on when you start your engine and may stay on for several seconds, that is normal.
A chime may also sound when the light comes on.
If the light stays on, or comes on when you are driving, your vehicle needs service. When the regular brake system warning light is not on, you still have brakes, but you do not have anti-lock brakes. If the regular brake system warning light is also on, you do not have anti-lock brakes and there is a problem with your regular brakes. See Brake System Warning Light earlier in this section.
The ABS warning light should come on briefly when you turn the ignition key to RUN. If the light does not come on then, have it fixed so it will be ready to warn you if there is a problem.
Antilock Brake System
When wheel slip is detected during a brake application, the ABS enters antilock mode. During antilock braking, hydraulic pressure in the individual wheel circuits is controlled to prevent any wheel from slipping. A separate hydraulic line and specific solenoid valves are provided for each wheel. The ABS can decrease, hold, or increase hydraulic pressure to each wheel brake. The ABS cannot, however, increase hydraulic pressure above the amount which is transmitted by the master cylinder during braking.
During antilock braking, a series of rapid pulsations is felt in the brake pedal. These pulsations are caused by the rapid changes in position of the individual solenoid valves as the EBCM responds to wheel speed sensor inputs and attempts to prevent wheel slip. These pedal pulsations are present only during antilock braking and stop when normal braking is resumed or when the vehicle comes to a stop. A ticking or popping noise may also be heard as the solenoid valves cycle rapidly. During antilock braking on dry pavement, intermittent chirping noises may be heard as the tires approach slipping. These noises and pedal pulsations are considered normal during antilock operation.
Vehicles equipped with ABS may be stopped by applying normal force to the brake pedal. Brake pedal operation during normal braking is no different than that of previous non-ABS systems. Maintaining a constant force on the brake pedal provides the shortest stopping distance while maintaining vehicle stability.
Programming the Traction Control Automatic Engagement Feature
The automatic engagement feature may be programmed so that the traction control system activates or does not activate automatically at the start of each ignition cycle. In order to change the status of the automatic engagement feature, perform the following procedure:
Important Failure to follow the correct procedure may cause DTC C0283 to set in EBCM memory.
- Park the vehicle and apply the parking brake.
- Unlock the ignition and shift the transmission into NEUTRAL (N).
- Turn the ignition ON, engine OFF.
- Press and hold the brake pedal and the accelerator pedal.
- Press and hold the traction assist switch for 5 seconds.
- Release the brake and accelerator pedals and the traction control switch.
- Turn the ignition OFF.