Technical Description of OBD-II Trouble Code
Issue with the Neutral Input Circuit
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to many OBD-II vehicles (1996-newer), including Land Rover, Volvo, BMW, Mini, Jaguar, etc. However, the exact repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
If your vehicle has stored a code P081D, it means that the powertrain control module (PCM) has detected a malfunction in the NEUTRAL input circuit of the neutral safety switch (also known as the shift selector switch). This code is only applicable to vehicles with automatic transmissions.
The NEUTRAL input circuit is usually integrated into the neutral safety switch or shift selector switch. When the transmission is in NEUTRAL, a voltage signal is sent to the transmission control module (TCM) or the PCM. The controller also monitors the circuit voltage when 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 the correct voltage on the NEUTRAL circuit when the transmission is apparently in park or neutral, a code P081D may be stored and the malfunction indicator lamp (MIL) may illuminate. Multiple ignition cycles (with a failure) may be necessary for MIL illumination.
What is the severity of this DTC?
A stored code P081D could result in a no-start condition and indicates that there has been an electrical issue or a mechanical failure. It is important to rectify the conditions that led to the storage of this code as quickly as possible.
What are some of the symptoms of the code?
Symptoms of a P081D trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P081D troubleshooting steps?
To diagnose a code P081D, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle-specific diagnostic information.
You can use your source of vehicle information to find a technical service bulletin (TSB) that matches the vehicle’s year, make, and model, as well as the engine size, stored code/s, and exhibited symptoms. If you find a TSB, it may provide helpful diagnostic information.
Use the scanner (connected to the vehicle diagnostic connector) to retrieve all stored codes and relevant freeze frame data. It is recommended to write down this information before clearing the codes and 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 point, the code is intermittent and may be more difficult to diagnose. In such cases, the conditions that led to the storage of 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 involve searching your vehicle information source for diagnostic flowcharts, connector pin-out charts, connector face views, and component testing procedures/specifications.
Step 1
Use the DVOM to test the NEUTRAL input voltage at the appropriate neutral position/shift selector switch. Typical NEUTRAL input circuits consist of either battery voltage (when activated) or ground (when deactivated).
Step 2
Use your source of vehicle diagnostic information and the DVOM to test the neutral safety/shift selector switches as required. 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 NEUTRAL input circuits to the PCM. Disconnect all controllers before using the DVOM for testing.
