Test P EBCM/EBTCM Open Switch Input

Antilock Brake System And Traction Control System Wiring Diagram:

*** THIS ARTICLE REFLECTS CHANGES MADE BY TSB #93811, DATED FEB, 93

OPERATION:
The EBCM/EBTCM monitors brake pedal position using the TOC/Antilock brake switch. The normally closed switch opens when the brake pedal is depressed approximately 40%. The EBCM/EBTCM also monitors pump motor operation using a pump motor run sensor.

During most ABS braking condition, the EBCM/EBTCM turns on the pump motor, replenishing the PMV assembly reservoir and applying fluid pressure to the master cylinder. This causes the brake pedal to gradually rise. The EBCM/EBTCM turns off the pump motor when brake pedal height rises sufficiently to close the TOC/Antilock brake switch.

The pressure modulator valve (PMV) fluid level switch alerts the EBCM/EBTCM to a low brake fluid condition in the PMV reservoir. The fluid level switch is located in the PMV assembly's reservoir. The fluid level switch is normally closed when the reservoir contains sufficient fluid. When fluid level is low, the switch opens, causing the EBCM/EBTCM to turn on the ANTILOCK indicator.

The pressure switch monitors primary brake system pressure. The normally closed switch opens when the brakes are applied (pressure exceeds 700 kPa) or (101 psi). If the brakes are manually applied during traction control mode, the PMV pressure switch input, along with the brake switch input, signal EBCM/EBTCM to disable traction control and allow manual braking. The pressure switch is part of the pressure modulator valve (PMV) assembly and is not serviceable.

DTC 72 sets when the EBCM/EBTCM detects that the TCC/Antilock brake switch CKT 848 is shorted to ground.

DTC 73 sets when the EBCM detects a short to ground in the PMV fluid level switch circuitry. These include CKTS 848, 849, 853 and 1659.

DTC 74 sets when the EBCM/EBTCM detects an open or short to ground in the PMV pressure switch circuitry.

POSSIBLE CAUSES:
Short to ground in CKT 848 with TCC/Antilock brake switch open.
Short to ground In CKT 848, 849, 853 or 1659.
Open in CKT 853 or 1659.
Short to ground in CKT 1659 with brake pedal depressed.
Failed PMV pressure switch.