Test T Main Relay Ground

Antilock Brake System And Traction Control System Wiring Diagram:

T: Main Relay Ground System:

FOR UPDATED INFORMATION NOT INCLUDED HERE, REFER TO TSB #9389, DATED JAN. 93

OPERATION:
When the ignition switch is first turned to RUN, the EBCM/EBTCM goes through a self-test lasting 2-4 seconds. During this test, the EBCM/EBTCM grounds terminal 52, causing the amber ANTILOCK indicator to light. This serves as an indicator bulb test. The EBCM/EBTCM also grounds terminal 34, energizing the main relay. This removes the indicator ground path provided through the anti-lock diode and the main relay contacts.

When the self-test is completed (and no faults are detected), the EBCM/EBTCM removes the ground at terminal 52, turning off the indicator. The main relay remains energized.

When the EBCM/EBTCM detects a fault, it grounds terminal 52, causing the amber ANTILOCK indicator to light.

NOTE: The ESCM/EBTCM also de-energizes the main relay, creating a redundant ground path.

When the EBCM/EBTCM is disabled for any reason (i.e. open fuse 19), the main relay is de-energized. This provides an ANTILOCK indicator ground path through the antilock diode and main relay contacts, and causes the indicator to light with no codes being set.

POSSIBLE CAUSES:
Open In CKT 803, 852 or 1077.
Open bulb.
Short to voltage in CKT 852.
Open or shorted antilock diode.
Main relay falls "engaged."
Short to ground In CKT 855.
See Electrical Schematic Part 1 of 3 to CKT 803 at Main Relay