What Does It Mean?
This diagnostic trouble code (DTC) is a generic powertrain code and applies to many OBD-II vehicles (1996-newer). This may include, but is not limited to, vehicles from Toyota, Land Rover, Volvo, BMW, Mini, Jaguar, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.
If your vehicle has stored a P0818 code, it means that the powertrain control module (PCM) has detected a malfunction in the transfer case neutral safety switch circuit (also known as the shift selector switch). This type of code applies only to vehicles equipped with AWD/4WD automatic transmissions.
The transfer case neutral safety switch input circuit is typically integrated into the neutral safety switch or the shift selector. When the transfer case is placed in neutral (drivetrain disconnected), a voltage signal is input to the transmission control module (TCM) or the PCM. The controller also monitors the voltage of the transfer case neutral safety switch circuit whenever the ignition is in the ON position. The TCM may be a standalone module or part of the PCM.
If the PCM does not detect an appropriate voltage level on the transfer case neutral safety switch circuit, with the transfer case apparently in gear or neutral, a P0818 code may be stored and a malfunction indicator lamp (MIL) illuminated. Multiple ignition cycles (with a failure) may be required for the MIL to light up.
How Severe Is This DTC?
A stored P0818 code may be accompanied by a no-start condition and also indicates that an electrical issue or a serious mechanical failure has occurred. The conditions that contributed to storing a code of this nature should be rectified as soon as possible.
What Are Some of the Symptoms of the Code?
Symptoms of a P0818 fault code may include:
Engine does not start
Front axle does not engage or disengage
Engine starts with the transmission in gear
No symptoms may be present
What Are Some Common Causes of the Code?
Causes
of this code may include:
Faulty neutral safety switch or shift selector
Shorted or open wiring or connectors in the transfer case neutral safety switch input circuit
Faulty PCM or programming error
What Are the P0818 Troubleshooting Steps?
A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle-specific diagnostic information will be needed to diagnose a P0818 code.
You can use your vehicle information source to locate a technical service bulletin (TSB) that matches the vehicle’s year, make, and model; as well as engine size, stored codes, and presented symptoms. If you find one, it may provide useful diagnostic information.
Use the scanner (connected to the vehicle’s diagnostic connector) to retrieve all stored codes and relevant freeze frame data. It is a good idea to record this information before clearing the codes, then test the vehicle until the PCM enters readiness mode or the code resets.
If the PCM enters readiness mode at that point, the code is intermittent and may be much more difficult to diagnose. If this is the case, the conditions that contributed to storing the code may need to worsen before an accurate diagnosis can be made.
If the code is immediately reset, the next step in your diagnosis will require you to consult your vehicle information source for diagnostic flowcharts, connector pinout diagrams, connector face views, and component testing procedures/specifications.
Step 1
Use the DVOM to test the voltage input of the transfer case neutral safety switch with the gear lever in different positions. Typical transfer case neutral safety switch input circuits consist of either battery voltage (when activated) or ground (when deactivated).
Step 2
Use your vehicle diagnostic information source and the DVOM to test the neutral safety/shift selector switches, if necessary. Replace switches that do not test within system parameters.
Step 3
If the system switches and circuits are functional, use the DVOM to test the transfer case neutral safety switch input circuits to the PCM. Disconnect all controllers before using the DVOM for testing.
Transfer case neutral safety switch input codes are most often attributed to a failure of the neutral safety switch