Diagnostic Overview
NON-eBOOSTER SYSTEM: When any faults are present against the BPP Sensor in the BSCM or PCM, the sensor and circuits should always be checked before condemning a module. While the Master Cylinder Pressure Sensor and hydraulic circuit pressure sensors are inside the HCU, the connection between the HCU and BSCM should always be checked for proper connection, burnt, corroded or damaged terminals before condemning the HCU. If the BSCM is found to be the issue it can be replaced separately. If the HCU is determined to be the issue, the HCU and BSCM should be replaced as an ICU assembly.
eBOOSTER SYSTEM: While the BPP Sensors, Brake Pedal Simulator Pressure Sensor and hydraulic circuit pressure sensors are inside the HCU, the connection between the HCU and BSCM should always be checked for proper connection, burnt, corroded or damaged terminals before condemning the HCU. If the BSCM is found to be the issue it can be replaced separately. If the HCU is determined to be the issue, the HCU and BSCM should be replaced as an eBooster assembly.
WHEEL SPEED SENSORS: When the vehicle is moving, the Wheel Speed Sensor signals are rationalized against each other for a stuck sensor. The controller is able to determine difference between a fault and a normal vehicle turning event (explained below).
| WHEEL SPEED SENSOR COMPARISONS MONITORED | |
|---|---|
| Left Front vs Right Front | LF/RF |
| Left Front vs Left Rear | LF/LR |
| Left Front vs Right Rear | LF/RR |
| Right Front vs Left Rear | RF/LR |
| Right Front vs Right Rear | RF/RR |
| Left Rear vs Right Rear | LR/RR |
The enable condition threshold is used as the comparison threshold. The threshold is calculated by taking the average of the six comparison calculations in the table when the vehicle is moving.
- Driving Straight - When the vehicle is moving in a straight line (steering wheel angle is near zero) the four sensor signal outputs should be relatively equal. If the LF sensor was stuck, the difference in the three calculations between the LF and other three sensors (LF/RF, LF/LR, LF/RR) will be above the enable condition threshold and the other three calculations (RF/LR, RF/RR, LR/RR) will be below the enable condition threshold, indicating a LF Wheel Speed Sensor failure.
- Turning - When the vehicle is turning all of the comparison checks will be different. The differences for all of the comparison checks will increase as the turning radius increases. If all comparison checks are above the calculated enable condition threshold, the vehicle is considered to be in a significant turning event and the diagnostic is temporarily disabled.
- Vehicle Stopped - When the vehicle is stopped each Wheel Speed Sensor signal should be 0. If three sensor outputs equal 0 and the forth is above 0 for a calibrated period threshold, the sensor is determined to be irrational.