P0688
ECM/PCM Power Relay Sense Circuit/Open
P0688 is an OBD-II diagnostic trouble code meaning: ECM/PCM Power Relay Sense Circuit/Open. Common causes: open circuit for monitoring the ecu power relay, short circuit in control circuit. Estimated repair cost: $6–111.
Symptoms
- Check Engine Light
- Possible unstable engine operation
- Malfunctions of electronic systems
- The ECU does not confirm that the power relay is turned on
- Difficult or unpredictable engine starting
Causes
- Open circuit for monitoring the ECU power relay
- Short circuit in control circuit
- ECU power relay malfunction
- Oxidation or damage to connectors
- Internal ECU fault
How to Fix
- Read OBD-II codes
- Locate the control circuit of the ECU power relay according to the electrical diagram
- Measure the voltage in the control circuit (the standard corresponds to the manufacturer’s specifications)
- Check the circuit for open circuit and short circuit
- Check the relay and its connector
- If the external circuit is working properly - ECU diagnostics
Related codes
Error P0688 by Vehicle Brand
FAQ
What does the P0688 code mean?
P0688 is an OBD-II diagnostic trouble code that indicates: ECM/PCM Power Relay Sense Circuit/Open
What causes a P0688 error code?
The most common causes of P0688 include: Open circuit for monitoring the ECU power relay; Short circuit in control circuit; ECU power relay malfunction; Oxidation or damage to connectors.
How do I fix a P0688 diagnostic trouble code?
To fix P0688: Read OBD-II codes. Locate the control circuit of the ECU power relay according to the electrical diagram. Measure the voltage in the control circuit (the standard corresponds to the manufacturer’s specifications). For a complete diagnosis, use an OBD-II scanner.
Is it safe to drive with P0688?
Do not drive — repair immediately
How much does it cost to fix P0688?
The estimated repair cost for P0688 is $6–111. Actual cost depends on your vehicle, location, and labor rates.
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