Powertrain

P1391 - FAULT CODE - OBD2

Table Of Contents

    Description of DTC code P1391 Generic

    The G-Sensor (Road Sensor) is a vertical low acceleration sensor with gravity (G) detection. When vertical acceleration that is caused by potholes is detected, the ECM (Engine Control Module) can take action and determine if the changes in crankshaft speed are due to engine misfiring, or if they are induced by the transmission line instead. If the G-Sensor notices a hard road condition, the ECM‘s misfire detection diagnosis will be activated.

    When the G-Sensor is at rest, the output of the sensor should be between 2.35 to 3.65 volts (+1G) and during a difficult road condition, the voltage output may vary between 0.5v (-1G) and 4.5v (+3G).

    If during the operation of the vehicle’s engine, voltage changes are detected in the G-Sensor, which are not within the parameters already set by the manufacturer, the diagnostic code P1391 OBDII will be stored. However, it should be noted that the G-Sensor shares the 5-volt reference of the ECM and the ground terminals with the A/C Pressure Sensor. Therefore, if the A/C Pressure Sensor or its wiring is damaged, the code P1391 can be set.

    Symptoms of fault code P1391 Generic

    Causes of OBD2 P1391 Generic

    The reasons why the fault code P1391 OBD2 is set are

    • The G-Sensor circuit cables or connectors may be damaged.
    • The Engine Control Module may have deficiencies in the electrical connections.
    • The G-Sensor may be defective.

    Possible solutions of the DTC code P1391 Generic

    The steps to follow to solve the DTC code P1391 OBDII are

    • See the Technical Service Bulletins (TSB).
    • Check the ECM's harness connections to verify that the terminals are properly connected and do not have high levels of corrosion. Make any necessary corrections.
    • Verify that the G-Sensor wiring is in good condition. If the entire harness appears to be fine, use a scanning tool to observe the sensor screen while moving the sensor connectors and wire harnesses. Any changes to the display are due to wiring failures. Repair as applicable.
    • Note that the G-Sensor shares the 5-volt reference of the ECM and the ground terminals with the A/C Pressure Sensor. Therefore, if the A/C Pressure Sensor or its wiring is damaged, the code P1391 can be set.
    • Check that the voltages of Sensor G are as indicated in the manufacturer's specifications. Only if the sensor is level and securely installed in its holder will the voltages be adequate.

     

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