PCM Power and Ground Check

Circuit Description

The PCM is fed battery voltage at all times at PCM connector C1 terminals 20 and 61 through CKT 240 from the Underhood Junction Block, fuse A1. IGN 1 voltage (Hot in Run, Bulb Test or Start) is fed through CKT 39 and the Underhood Junction Block, fuse C7 to PCM connector C1 terminal 19 and C2 terminal 37. IGN 0 voltage (Hot in all positions except LOCK) is fed from the ignition switch CKT 1390 to PCM connector C1 terminal 18. The PCM needs all of these inputs to function properly. Refer to Power Distribution Schematics or to Ground Distribution Schematics in Diagrams.

The PCM also has four grounding points: at terminals 21 and 60 of both PCM connectors C1 and C2. These terminals are grounded through CKT 1551 to ground G102.

Diagnostic Aids

Ensure that the battery is fully charged and tested before performing this check.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

2. Checking battery power supply to the PCM.
5. Checking Ignition 0 voltage to the PCM.
7. Checking Ignition 1 and Ignition Supplement voltage to the PCM.
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.







Powertrain Ground Check

Refer to Locations for component location views.

Circuit Description

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 PCM Power and Ground Check (2 of 2) should be performed when referred to by other diagnostics or when erratic or intermittent problems defy traditional diagnosis. The PCM Power and Ground Check (2 of 2) chart lists these grounds and other pertinent information that will allow you to investigate a possible loose or faulty ground connection.

Diagnostic Aids

Check the grounds listed in the Powertrain Ground Check table for the following conditions:

^ Corrosion or paint between the ring terminal and the grounding surface
^ Poor quality crimp of the ring terminal to the ground wire
^ Damaged ground wire