DESCRIPTION & OPERATION
| WARNING | Vehicles are equipped with air bag supplemental restraint system. Before attempting any repairs involving steering column, instrument panel or related components, see SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM in appropriate AIR BAG RESTRAINT SYSTEMS article. |
The primary purpose of the Brake Assist system is to provide an auxiliary brake force assist to the driver who cannot generate a large brake force during emergency braking, thus maximizing the vehicle's brake performance.
The ABS (Anti-Lock Brake System) helps to prevent the tires from locking up, thereby ensuring vehicle performance and handling ability.
The EBD (Electronic Brake force Distribution) system distributes optimal breaking force to the front and rear tires in accordance with driving conditions. Furthermore, braking force is distributed to the left and right wheels during braking when cornering to ensure vehicle performance and superior braking power.
The TRAC system helps prevent the drive wheels from slipping if the driver presses the accelerator pedal excessively when starting off or accelerating on a slippery surface.
The VSC system helps prevent the vehicle from slipping sideways as a result of strong front wheel skid or rear wheel skid during cornering.
When trouble shooting is conducted for Multiplex OBD (M-OBD) vehicles, the only difference from the usual trouble shooting procedure is the LEXUS hand-held tester is to be connected to read off various data output from the vehicle's skid control ECU. The skid control ECU records the corresponding DTC when the computer detects a malfunction in the computer itself or its circuit. To check DTC, connect the hand-held tester to DLC3 on the vehicle. The hand-held tester enables you to erase DTC and activate the several solenoids and actuators, and check freeze frame data and various forms on skid control data. (Scheme 20)
For component locations (Scheme 21)
Scheme 20
Scheme 21
Actuator Motor Operation
- With the motor relay ON, check the actuator motor operation noise.
- Turn the motor relay OFF. Depress the brake pedal and hold it for about 15 seconds. Check that the brake pedal cannot be depressed.
- Turn the motor relay ON and check that the pedal does not pulsate.
- Turn the motor relay OFF and release the brake pedal.
Wheel Solenoid Operation
- Depress the brake pedal, turn the SFRH and SFRR (right front wheel) solenoid ON simultaneously and check that the pedal cannot be depressed.
- Turn the SFRH and SFRR solenoid OFF simultaneously and check that the pedal can be depressed.
- Turn the motor relay ON and check that the pedal returns.
- Turn the motor relay OFF and release the brake pedal.
- Using the same procedure, check the solenoids of the other wheels. Left front wheel is SFLH and SFLR. Right rear wheel is SRRH and SRLR and left rear wheel is SRLH and SRLR.