P0688
P0688-AUTO SHUTDOWN RELAY SENSE CIRCUIT LOWP0688-Auto Shutdown Relay Sense Circuit Low:
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
- Internal 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.
Q: Does the DTC reset?
YES: Go To 2
NO: Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Component Tests and General Diagnostics
Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
2. ENGINE OPERATION
Attempt to start the engine.
Q: 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 C3 PCM harness connector.
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.
Q: Is the resistance below 5.0 ohms?
YES: Go To 7
NO: Repair the open in the (A955) ASD Relay Output circuit. Perform the 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.
Q: Does the DTC reset?
YES: Go To 5
NO: Replace the ASD Relay. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
5. INTERNAL FUSED B+ CIRCUITS
Turn the ignition off.
Using a 12-volt test light connected to ground, probe the Internal Fused B+ circuits at the Relay connection.
Q: Does the test light illuminate brightly?
YES: Go To 6
NO: Repair the open or short to ground in the Internal Fused B+ circuits. Inspect the related fuse and repair as necessary. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
6. (A955) ASD RELAY OUTPUT CIRCUIT OPEN
Disconnect the C3 PCM harness connector.
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.
Q: Is the resistance below 5.0 ohms?
YES: Go To 7
NO: Repair the open in the (A955) ASD Relay Output circuit. Perform the 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.
Q: Were there any problems found?
YES: Repair as necessary. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Replace and program the Powertrain Control Module. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test