P0688 Auto Shutdown Relay Sense Circuit Low

P0688 code - When monitored this DTC with the ignition on, battery voltage greater than 10.0 volts. No voltage sensed at the Powertrain Control Module (PCM) when the ASD relay is energized. This is a non MIL fault. If the vehicle is equipped with the stop/start feature, the system will be disabled when this DTC is active.

P0688


Possible causes P0688 code

- ASD relay output circuit open
- ASD relay output circuit shorted to ground
- ASD relay
- Totally Integrated Power Module (PCM)

Diagnose P0688 code

Step 1. Check for an active DTC
If the P0685 and P0688 DTCs are both present, diagnose and repair the P0685 DTC before the P0688. If equipped with a removable relay, verify that the are no concerns with the circuits and fuses that supply power to the ASD relay. Look for bent or corroded terminals. Verify that the ASD relay is not defective (exchange with known good relay to check opeartion).
Turn the ignition on, with the scan tool read DTCs and record on the repair order.

Is the DTC active or pending?

Yes, go to step 2.
No, perform the PCM intermittent condition.

Step 2. Powertrain Control Module (PCM)
Turn the ignition off, disconnect the PCM C1 harness connector, turn the ignition on measure the voltage on each of the ASD relay output circuits at the PCM harness connector.

Is the voltage equal to battery voltage at each terminal when the ignition is turned on?

Yes, check for any service bulletins that may apply. Look for broken, bent, pushed out or corroded terminals. Verify the that there is good pin to terminal contact in the Powertrain Control Module connectors. If no concerns are found, replace and program Powertrain Control Module (PCM). Perform the Powertrain Verification Test.

No, go to step 3.

Step 3. Check the ASD control output circuit(s) for a short to ground
Turn the ignition off, disconnect the PCM C1 harness connector. Disconnect the appropriate TIPM harness connector, check for continuity between ground and ech of the ASD control output circuita at the TIPM harness connector.

Is there continuity between ground and any of the ASD control output circuits?

Yes, repair the ASD control output circuit for a short to ground.
No, go to step 4.

Step 4. Check the ASD control output circuit (s) for an open/high resistance
Turn the ignition off, measure the resistance of each ASD control output circuit between the TIPM harness connector and the PCM C1 harness connector.

Is the resistance below 3.0 Ohms?

Yes, go to step 5.
No, repair the ASD control output circuit for an open or high resistance.

Step 5. Check related PCM and component connections

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