P0688

P0688-AUTO SHUTDOWN RELAY SENSE CIRCUIT LOW






For a complete wiring diagram refer to: Electrical Diagrams

When Monitored
With ignition key on. Battery voltage greater than 10 volts.

Set Condition
No voltage sensed at the PCM when the ASD relay is energized. One Trip Fault. Three good trips to turn off the MIL.

Possible Causes
- (A922) FUSED B+ CIRCUITS
- (A955) ASD RELAY OUTPUT CIRCUIT OPEN
- ASD RELAY
- PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test
1. VERIFY ASD DTC





NOTE: Diagnose P0685 - Auto Shutdown Relay Control Circuit first if it set along with this DTC.

With a scan tool, erase the DTC.
Attempt to start the engine. If the engine will not start, crank the engine for at least 15 seconds. It may be necessary to repeat several times.

Does the DTC reset?
Yes >> Go To 2
No >> Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
2. ENGINE OPERATION
Attempt to start the engine.

Does the engine start?
Yes >> Go To 3
No >> Go To 4
3. (A955) ASD RELAY OUTPUT CIRCUIT OPEN





Turn the ignition off.
Remove the ASD Relay Disconnect the PCM harness connectors.

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.

Measure the resistance of the (A955) ASD Relay Output circuit from the Relay connection to the appropriate terminals of special tool #8815.

Is the resistance below 5.0 ohms?
Yes >> Go To 7
No >> Repair the open in the (A955) ASD Relay Output circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
4. ASD RELAY
Turn the ignition off.
Install a substitute relay in place of the ASD Relay.
Ignition on, engine not running.
With a scan tool, erase DTCs.
Attempt to start the engine.
With a scan tool, read DTCs.

Does the DTC reset?
Yes >> Go To 5
No >> Replace the ASD Relay.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
5. (A922) FUSED B+ CIRCUITS





Turn the ignition off.
Using a 12-volt test light connected to ground, probe the (A922) Fused B+ circuits at the Relay connection.

Does the test light illuminate brightly?
Yes >> Go To 6
No >> Repair the open or short to ground in the (A922) Fused B+ circuits. Inspect the related fuse and repair as necessary
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
6. (A955) RELAY OUTPUT CIRCUIT OPEN





Disconnect the PCM harness connectors.

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.

Measure the resistance of the (A955) ASD Relay Output circuit from the Relay connection to the appropriate terminals of special tool #8815.

Is the resistance below 5.0 ohms?
Yes >> Go To 7
No >> Repair the open in the (A955) ASD Relay Output circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
7. PCM

NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.

Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.

Were there any problems found?
Yes >> Repair as necessary
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Replace and program the Powertrain Control Module per Service Information.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test