PCM Power and Ground Check

Circuit Description

PCM Power and Ground
The PCM is fed battery voltage at all times at PCM connector C1 terminals 20 and 61 through CKT 1642 from the 20 amp fuse. IGN 1 voltage, Hot in Run, Bulb Test or Start, is fed through CKT 439 and 10 amp fuse to PCM connector C1 terminals 18 and 19 and C2 terminal 37. The PCM needs all of these inputs to function properly. The PCM also has four grounding pins: at terminals 21 and 60 of both PCM connectors C1 and C2. These terminals are grounded through CKT 451 to ground G101.

Powertrain Ground Check
There are several vehicle grounds that are essential for proper powertrain system operation. Loose or poor ground connections may cause widely varying problems, from flickering telltales to PCM DTCs to driveability problems. The Powertrain Ground Check should be performed when referred to by other diagnostics or when erratic or intermittent problems defy traditional diagnosis. The Powertrain Ground Check table lists these grounds and other pertinent information that will allow you to investigate a possible loose or faulty ground connection.

Diagnostic Aids
Ensure that the battery is fully charged and tested before performing these checks.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
2. Checking battery power supply to the PCM.
If voltage is OK, repeat this step with a test lamp to verify the circuit has good connections that will flow adequate current.
7. Checking Ignition 1 and Ignition Supplement voltage to the PCM.
If voltage is OK, repeat this step with a test lamp to verify the circuit has good connections that will flow adequate current.
9. Checking ground supply to the PCM. If PCM grounds are good, perform the Powertrain Ground Check to diagnose other vehicle grounds that may cause driveability complaints.
If resistance is OK, check the ground circuits with a test lamp to battery voltage. This will verify the circuit has good connections that will flow adequate current.