Test One

PCM Power And Ground Chart (1 Of 3):

PCM Power And Ground Circuits:

CIRCUIT DESCRIPTION
The PCM is fed battery voltage at all times at pins "C4" and "D4" through CKT 1642 from the rear fuse block. The PCM is also fed IGN 1 (HOT IN RUN BULB TEST and START) at pin "D5" through CKT 439 from the I/P fuse block. The PCM needs both battery and IGN 1 voltages to operate.

The PCM also has four grounding points at pins "C2", "C3", "D2", and "D3" through CKT 251 to G100.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Checking for UART (Universal Asynchronous Receiver Transmitter) communications, data line code(s) that would indicate the entire data line is down.
2. Checking for battery voltage on CKT(s) 1642. Voltage should be measured at both PCM harness connectors "C4" and "D5". If voltage is not present on both circuits, check for open at splice, in-line engine harness connector, or 20 amp PCM/VATS fuse.
3. Checking CKT 439 and fuse for an open.
4. Checking CKT 251 for an open. If voltage measures above 0.1 volt on 1 to 3 wires, repair open to S226. If voltage measures above 0.1 volt on all four wires, repair the open from S226 to G100.
5. Checking for an open in CKT 251 or faulty PCM.
6. Checking if the UART communications data line is open, shorted to ground, or shorted to voltage on the data line is causing a PCM problem.