Description of DTC code P0686

Most OBDII equipped vehicles are equipped with an Engine Control Module (ECM) / Powertrain Control Module (PCM) relay. This relay provides battery voltage and ground to the computer. For the relay to function properly, a battery voltage signal, a ground signal and an ignition switch input signal must be present. Additionally, there is an output signal that is used to send data to the ECM or PCM.

If the vehicle's main computer detects that there is a voltage level outside the range specified by the manufacturer, it will illuminate next to the Check Engine light the DTC P0686 OBD2 code.

Symptoms of fault code P0686

  • MIL (Malfunctioning Engine) light on.
  • Engine may not start.

Causes of OBD2 P0686

The reasons for the P0686 OBDII fault code being set are:

  • The ignition switch is possibly faulty.
  • The PCM power relay may be faulty.
  • A fuse related to the system may be blown.
  • A poor connection at the ends of the battery cables.
  • The connectors or wires associated with the relay may be corroded.

Possible solutions of the DTC code P0686

Troubleshooting steps related to the P0686 OBD2 fault code are as follows:

  • Consult the Technical Service Bulletins specific to your vehicle model.
  • Inspect the wiring harnesses and system connectors. Look for any delays that may be affected by corrosion. Also check that the battery cables are correctly adjusted. Repair or replace any of these components that have defects.
  • Use the vehicle's information source to find the location of the PCM power relay, then use a digital meter to check the battery voltage at the main input terminal of the power relay. If there is no voltage at the terminal, it is due to a blown or bad fuse. Likewise check the voltage at the secondary input terminal. Change as necessary.
  • Verify that the power relay has a ground signal. Repair if no ground signal is present.
  • Test the relay input voltage at the PCM If no voltage is present at the connector, check the system circuitry.

Codes related to P0686

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