Chart B-4 Loss of Power to BCM

Chart B-4:

CPS To BCM Interface:

DESCRIPTION:

This chart is used because the odometer, at key on, reads all zeroes and the courtesy lamps did not turn on when the switch was actuated. These symptoms indicate the BCM has lost power or ground with the Central Power Supply (CPS).

NOTE ON FAULT TREE:

1. Checking for maximum blower speed with key "ON" will indicate whether the BCM has lost logic ground (CKT 801E) with the CPS.

2. This step determines if the loss of logic ground is due to the BCM, the CPS, or the 801E wire and terminals.

3. This step checks for 12 volts to the BCM. If 12 volts is not present at the BCM, then the fault is due to the CPS or the wiring.

4. This step checks for 7 volts to the BCM, which has two individual inputs fed from the CPS. Loss of both signals would result in a system fault otherwise the fault is due to a bad CPS or BCM.