Description of DTC code P0688

The DTC P0688 OBDII code setting shows that the PCM (Powertrain Control Module) has found a problem with the relay supplying voltage to the vehicle's computer. This code refers to the circuit being disconnected.

This relay applies battery voltage to the PCM circuitry in a safe way. It is initiated with a signal wire that comes from the ignition switch. It usually uses 5 wires. With one wire the battery voltage is applied, another one for the ground, a third wire carries the signal from the switch, a fourth one supplies voltage to the PCM and the fifth wire is from the power relay sensing circuit. This circuit is monitored by the PCM to monitor voltage to the power relay.

Symptoms of fault code P0688

  • Check Engine light ON.
  • A difficult start.
  • The engine may not start.

Causes of OBD2 P0688

The P0688 OBD2 fault code is set due to the following reasons:

  • The PCM power relay may be faulty.
  • Perhaps there are corroded, loose or bad electrical connections.

Possible solutions of the DTC code P0688

To troubleshoot errors caused by the P0688 OBDII diagnostic code, please note the following:

  • Check that the battery charge level is right. Charge it if it is discharged.
  • Check the cables and connectors related to the system. If you find broken or mismatched cables, repair or replace them.
  • Change the related fuses.

Codes related to P0688

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