P090

Circuit Description

This diagnostic test functions on the assumption that a sudden decrease in non-drive (rear) wheel speed must be caused by a brake application. Non-drive wheel speed and stop lamp switch status are supplied to the PCM through serial data from the Electronic Brake and Traction Control Module (EBTCM). If there is a 2.5 mph or greater decrease of non-drive wheel speed in 0.2 second and a transition of the extended travel brake contacts of the TCC brake switch or stop lamp brake switch without a transition of the TCC switch contacts of the TCC brake switch the counter is incremented. When the counter reaches 5, Code P090 is set. The counter will be reset to zero if a transition of the TCC contacts of the TCC brake switch is noticed before the counter reaches 5.

Test Condition(s)

1. Codes P033, P106 and P137 not set.
2. Traction control and antilock brake systems are operating normally.
3. Non-drive wheel speed of 36 mph or greater.
OR
Non-drive wheel speed of 36 mph or greater and has not fallen below 1.2 mph since.

Failure Condition(s)

1. A 2.5 mph or greater decrease in non-drive wheel speed in 0.2 second.
2. Transition in the extended travel brake contacts of the TCC brake switch or Stop/BTSI/Cruise brake switch.
3. No transition noticed in the TCC contacts of the TCC brake switch.
4. If conditions 1 through 3 are true, increment counter.
5. When counter reaches 5, set Code P090.

Action Taken

1. Traction control disabled.
2. PCM disables cruise control.
3. PCM will substitute the status of the Stop/BTSI/Cruise brake switch input for the TCC brake switch input.
4. 'TRACTION DISABLED' and 'REDUCED ENGINE POWER' message displayed on the DIC.
5. Garage shift adapts are maintained at current levels.

Notes on Fault Tree

1. Testing torque converter clutch brake switch input to the PCM PI71. If the input is working correctly, the display will change from 'HI' to 'LO' to 'HI'. If display remains 'HI', check CKT 420 and TCC brake switch for a short to voltage. If display remains 'LO', check CKT 420 for an open or short to ground.
2. Checking for voltage present at TCC brake switch connector pin A.
3. Checking CKT 750 for a short to ground.
4. Checking CKT 420 for a short to ground. If CKT 420 OK, then CKT 750 is open.
5. Checking CKT 420 for an open.