P033

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 TCC contacts at the TCC brake switch or stop lamp switch without a transition of the extended travel contacts of the TCC brake switch the counter is incremented. When the counter reaches 5, Code P033 is set. The counter will be reset to zero if a transition of the extended travel contacts of the TCC brake switch is noticed before the counter reaches 5.

Test Condition(s)

1. Codes P090, 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 has been 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 TCC contacts of the TCC brake switch or Stop/BTSI/Cruise brake switch.
3. No transition noticed in the extended travel contact of the TCC brake switch.
4. If conditions 1 through 3 are true, increment counter.
5. When counter reaches 5, set Code P033.

Action Taken

1. PCM disables cruise control.
2. PCM will substitute the status of the TCC contacts of the TCC brake switch input for the extended travel input.
3. PCM turns 'ON' the 'SERVICE VEHICLE SOON' message.

Notes on Fault Tree

1. PCM input P186 should cycle from 'HI' to 'LO' to 'HI' when brake pedal is depressed and then released. If P186 remains 'LO', there is an open or short to ground in the system. If P186 remains 'HI', there is a short to voltage in the system.
2. If 10 volts or greater is measured, check CKT 1725 or TCC brake switch for an open. If less than 10 volts is measured, check CKT 350 and CKT 1725 for a short to ground.