P102

Circuit Description

The brake booster vacuum sensor changes resistance based on the vacuum inside the brake booster. This diagnostic test checks for a vacuum sensor reading which would be caused by a shorted sensor or a short on CKT 1726 or an open on CKT 476 (i.e. sensor voltage 5 volts (82 kPa VAC) or greater). Every time the TCC brake switch cycles from closed to open with the engine not at idle, this test checks for a shorted vacuum signal. If a shorted vacuum signal is detected for five consecutive cycles of the TCC brake switch, Code P102 will set. Any cycle of the TCC brake switch where a shorted vacuum signal is not detected will reset the counter to zero.

Test Condition(s)

1. Codes P031, P032, P034, and P071 not set.
2. One second has passed since the TCC brake switch was cycled from closed to open.
3. MAP value 30 kPa or greater (engine not at idle) for one second
4. If conditions 1 through 3 are true, and brake booster vacuum signal is 82 kpa or greater, increment failure counter.
5. If conditions 1 through 3 are true and brake booster vacuum signal is less than 82 kPa, reset failure counter to '0'.

Failure Condition(s)

Failure counter at 5 or greater.

Action Taken

1. PCM turns 'ON' the 'SERVICE VEHICLE SOON' message.

Notes on Fault Tree

1. PCM data PD84 will read 82 kPa to 84 kPa with the sensor shorted. If it does not, fault is not present.
2. If PCM data PD84 reads -11 kPa to -8 kPa with the sensor unplugged, then either CKT 476 is open or the sensor is shorted.
3. Checking CKT 1726 for a short to voltage.