I have a 97 Wrangler Sport with a 4.0L 6cyl. When ever I apply my brakes at low speeds my ABS activates but works normally at higher speeds. I have replaced all 4 brakes, L/F wheel bearing and U Joint and the vehicle speed sensor. The ABS light did not activated on my dash until I removed the fuse from under the hood. The brakes work nornally with the fuse removed.
abs activates at low speed
- Thread starter bro238
- Start date
Welcome to Jeepz.com. I just to the liberty of moving your post to the TJ forum.
SteelHeadz
Super Moderator
Was there any issue with the ABS prior to replacing the left front hub and bearing unit?.
Battery voltage is supplied to the CAB ignition terminal when the ignition switch is turned to Run position. The CAB performs a system initialization procedure at this point. Initialization consists of a static and dynamic self check of system electrical components.
The static check occurs after the ignition switch is turned to Run position. The dynamic check occurs when vehicle road speed reaches approximately 10 kph (6 mph) During the dynamic check, the CAB briefly cycles the pump and solenoids to verify operation.
If an ABS component exhibits a fault during initialization, the CAB illuminates the amber warning light and registers a fault code in the microprocessor memory. Is there any DTC stored in the CAB module?.
I suggest that you do re-check on the sensor connectors. Make sure the pins are not bent and the connectors are engaged and locked properly. The symptom you described appears that one of the sensor is not working properly and is sending a false signal or the lack there of to the ABS control module.
How it works:
The CAB monitors wheel speed sensor inputs continuously while the vehicle is in motion. However, the CAB will not activate any ABS components as long as sensor inputs and the acceleration switch indicate normal braking.
During normal braking, the master cylinder, power booster and wheel brake units all function as they would in a vehicle without ABS. The HCU components are not activated.
ANTILOCK BRAKING
The purpose of the antilock system is to prevent wheel lockup during periods of high wheel slip. Preventing lockup helps maintain vehicle braking action and steering control.
The antilock CAB activates the system whenever sensor signals indicate periods of high wheel slip. High wheel slip can be described as the point where wheel rotation begins approaching zero (or lockup) during braking. Periods of high wheel slip occur when brake stops involve high pedal pressure and rate of vehicle deceleration.
The antilock system prevents lockup during high slip conditions by modulating fluid apply pressure to the wheel brake units.
Brake fluid apply pressure is modulated according to wheel speed, degree of slip and rate of deceleration. A sensor at each wheel converts wheel speed into electrical signals. These signals are transmitted to the CAB for processing and determination of wheel slip and deceleration rate.
The ABS system has three fluid pressure control channels. The front brakes are controlled separately and the rear brakes in tandem. A speed sensor input signal indicating a high slip condition activates the CAB antilock program.
Two solenoid valves are used in each antilock control channel. The valves are all located within the HCU valve body and work in pairs to either increase, hold, or decrease apply pressure as needed in the individual control channels.
The solenoid valves are not static during antilock braking. They are cycled continuously to modulate pressure. Solenoid cycle time in antilock mode can be measured in milliseconds.
Removing the fuse for the ABS may erase the DTC on the module until it detects the fault again. Only then would be a good idea to get the DTC and see what it is.
Battery voltage is supplied to the CAB ignition terminal when the ignition switch is turned to Run position. The CAB performs a system initialization procedure at this point. Initialization consists of a static and dynamic self check of system electrical components.
The static check occurs after the ignition switch is turned to Run position. The dynamic check occurs when vehicle road speed reaches approximately 10 kph (6 mph) During the dynamic check, the CAB briefly cycles the pump and solenoids to verify operation.
If an ABS component exhibits a fault during initialization, the CAB illuminates the amber warning light and registers a fault code in the microprocessor memory. Is there any DTC stored in the CAB module?.
I suggest that you do re-check on the sensor connectors. Make sure the pins are not bent and the connectors are engaged and locked properly. The symptom you described appears that one of the sensor is not working properly and is sending a false signal or the lack there of to the ABS control module.
How it works:
The CAB monitors wheel speed sensor inputs continuously while the vehicle is in motion. However, the CAB will not activate any ABS components as long as sensor inputs and the acceleration switch indicate normal braking.
During normal braking, the master cylinder, power booster and wheel brake units all function as they would in a vehicle without ABS. The HCU components are not activated.
ANTILOCK BRAKING
The purpose of the antilock system is to prevent wheel lockup during periods of high wheel slip. Preventing lockup helps maintain vehicle braking action and steering control.
The antilock CAB activates the system whenever sensor signals indicate periods of high wheel slip. High wheel slip can be described as the point where wheel rotation begins approaching zero (or lockup) during braking. Periods of high wheel slip occur when brake stops involve high pedal pressure and rate of vehicle deceleration.
The antilock system prevents lockup during high slip conditions by modulating fluid apply pressure to the wheel brake units.
Brake fluid apply pressure is modulated according to wheel speed, degree of slip and rate of deceleration. A sensor at each wheel converts wheel speed into electrical signals. These signals are transmitted to the CAB for processing and determination of wheel slip and deceleration rate.
The ABS system has three fluid pressure control channels. The front brakes are controlled separately and the rear brakes in tandem. A speed sensor input signal indicating a high slip condition activates the CAB antilock program.
Two solenoid valves are used in each antilock control channel. The valves are all located within the HCU valve body and work in pairs to either increase, hold, or decrease apply pressure as needed in the individual control channels.
The solenoid valves are not static during antilock braking. They are cycled continuously to modulate pressure. Solenoid cycle time in antilock mode can be measured in milliseconds.
Removing the fuse for the ABS may erase the DTC on the module until it detects the fault again. Only then would be a good idea to get the DTC and see what it is.
here is my take on this. and this is exactly what is currently happening on my pickup. the abs sensor is on the unit bearing. after years of use, ther eis a small amount of rust scale that has developed under the sensor mount. This has cause a misallignment between the sensor and the tone ring so at slow speed, the sensor thinks the wheel is locked up. I simply pulled the sensor off and sanded the mounting spot, and reinstalled.. worked great for a couple years till it rusted again.
