Circuit/System Testing

PNP Switch Circuit Malfunction

1. Inspect the shift control cable for proper adjustment. Refer to Shift Control Cable Adjustment .
2. Inspect the PNP switch for proper adjustment. Refer to Park/Neutral Position Switch Replacement .
3. Ignition OFF. Disconnect the harness connector at the PNP switch.
4. Ignition ON. Probe the ground circuit terminal 1 with a test lamp that is connected to B+. Verify that the test lamp illuminates.
   • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
5. With the PNP switch disconnected, verify that the scan tool PNP Switch parameter is In Gear.
   • If not the specified value, test the signal circuit terminal 12 for a short to ground. If the circuit tests normal, replace the ECM.
6. Install a 3 A fused jumper wire between the ground circuit terminal 1 and the signal circuit terminal 12. Verify that the scan tool PNP Switch parameter is Park/Neutral.
   • If not the specified value, test the signal circuit terminal 12 for an open/high resistance. If the circuit tests normal, replace the ECM.
7. If all circuits test normal, test or replace the PNP switch.

Start Relay Circuit Malfunction

1. Ignition OFF, disconnect the STARTER RELAY. Refer to Relay Replacement (Within an Electrical Center) or Relay Replacement (Attached to Wire Harness) .
2. Ignition ON, transmission in Park/Neutral. Verify that a test lamp illuminates between the relay coil ground circuit terminal and B+.
   • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
3. Probe the STARTER RELAY switch B+ circuit terminal with a test lamp that is connected to ground. Verify that the test lamp illuminates.
   • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the STARTER RELAY fuse is open, test the relay controlled output circuit for a short to ground.
4. Connect a test lamp between the relay coil ground circuit terminal and the relay coil control circuit terminal.
IMPORTANT: The engine may begin to crank.
5. Ignition ON, transmission in Park/Neutral. Command the Starter Relay ON and OFF with a scan tool (LZ4), or turn the ignition switch between the START and RUN positions (L61). The test lamp should turn ON and OFF when changing between the commanded states.
   • If the test lamp is always ON, test the relay coil control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
   • If the test lamp is always OFF, test the relay coil control circuit for a short to ground or and open/high resistance. If the circuit tests normal, replace the ECM.
6. Connect the STARTER RELAY.
7. Install a test lamp between the starter X1-A terminal and ground.
IMPORTANT: The engine may begin to crank.
8. Ignition ON, transmission in Park/Neutral, command the Starter Relay ON with a scan tool (LZ4), or turn the ignition switch to the START position (L61). The test lamp should illuminate.
   • If the test lamp does not illuminate, test the relay controlled output circuit for an open/high resistance. If the circuit tests normal, test or replace the STARTER RELAY.
9. If all circuits test normal, test or replace the starter.