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Error Code P0818 is defined as Driveline Disconnect Switch Input Circuit. Error Code P0818 is a generic trouble code, meaning it applies to all vehicles with the OBD-II system, especially those made from 1996 up to present. This includes vehicles from, but not limited to, BMW, Mini, Jaguar, Toyota, Land Rover, and Volvo. Specifications on the definition, troubleshooting, and repairs, of course, vary between make,r model and powertrain configuration.
If the vehicle stores the Error Code P0818, this means the PCM (powertrain control module) has determined a malfunction in the transfer case neutral safety switch (also known as shift selector switch) circuit. This code only applies to AWD or 4WD automatic transmission vehicles.
The transfer case neutral safety switch input circuit is usually integrated into the neutral safety switch or the shift selector switch. When the transfer case is positioned in neutral (driveline disconnected), a voltage signal is sent to the transmission control module (TCM) or the PCM. The controller also checks the transfer case neutral safety switch circuit voltage if the ignition is at ON position. The TCM can be either a standalone module or part of the PCM.
If the PCM is unable to determine the right amount of voltage on the transfer case neutral safety switch circuit, with the transfer case apparently in or neutral, then this error code will be stored and will activate the Check Engine light. In some cases, multiple ignition cycles (with a failure) may be needed to activate the Check Engine light.
- Engine no start condition
- The engine starts with the transmission in gear
- Front axle unable to engage or will not disengage
In other cases, the vehicle may not show symptoms at all.
- Defective neutral safety switch or shift selector switch
- Shorted or open wiring/connector in the transfer case neutral safety switch input circuit
- Faulty or programming error in the PCM
How to Check
You will also need a diagnostic scanner, DVOM (digital volt/ohmmeter), and a source of vehicle diagnostic information.
Use the vehicle’s information to find the TSB (technical service bulletin) that matches the specifics of the vehicle (make, model, engine size, symptoms, and codes stored). This could help for a more thorough diagnosis.
Use the scanner (connected to the vehicle diagnostic connector) to retrieve all stored codes and pertinent freeze frame data. It is a good idea to write this information down before clearing the codes then test-drive the vehicle until the PCM either enters readiness mode, or the code is reset.
If the PCM enters readiness mode at this time, the code is intermittent and may be much more challenging to diagnose. If this is the case, the conditions which contributed to the code being stored may need to worsen before an accurate diagnosis can be made.
If the code is immediately reset, the next step of your diagnosis will require that you search your vehicle information source for diagnostic flow-charts, connector pin-out charts, connector face views, and component testing procedures/specifications.
Test the voltage, ground, and signal output at the right downshift switch using the DVOM. Typically, the downshift switch circuits consist of either the battery voltage (when activated) or the ground (if deactivated).
If all the system circuits are working correctly, then test the downshift switch circuits to the PCM or the transmission using the DVOM. Make sure you disconnect all controllers before using the DVOM for testing.
Test the downshift switches using your source of vehicle diagnostic information and the DVOM. Switches that don’t test within the system’s specifications must be replaced.
How to Fix
- Replacement of the transfer case neutral position switch
- Repair or replacement of faulty or damaged wiring or connectors associated with the neutral position switch
- Cleaning bad grounds for the neutral position switch
- Replacement or reprogramming of PCM (rare)
Error codes that refer to the transfer case neutral safety switch input are usually attributed to neutral safety switch failure.
This error code may come with a no-start condition, which means it is either an electrical or mechanical problem. Nevertheless, it should be addressed as soon as possible.