P081D Neutral Input Circuit
OBD-II Trouble Code Technical Description
Neutral Input Circuit
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code and applies to many OBD-II vehicles (1996-newer). That may include but is not limited to vehicles from Land Rover, Volvo, BMW, Mini, Jaguar, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration.
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 called the shift selector switch). This type of code is applicable to vehicles with automatic transmissions only.
The NEUTRAL input circuit is typically integrated into the neutral safety switch or shift selector switch. When the transmission is placed in NEUTRAL, a voltage signal is input to the transmission control module (TCM) or the PCM. The controller also monitors circuit voltage whenever the ignition is in the ON position. The TCM may be a stand alone module or part of the PCM.
If the PCM does not detect an appropriate degree of voltage on the NEUTRAL circuit, with the transmission apparently in park or neutral, a code P081D may be stored and a malfunction indicator lamp (MIL) illuminated. Multiple ignition cycles (with a failure) may be required for MIL illumination.
What is the severity of this DTC?
A stored code P081D could be accompanied by a no-start condition and also indicates that either an electrical issue or a mechanical failure has occurred. Conditions which contributed to a code of this nature being stored should be rectified as quickly as possible.
What are some of the symptoms of the code?
Symptoms of a P081D trouble code may include:
Engine will not start Engine starts with the transmission in gear No symptoms may be exhibitedWhat are some of the common causes of the code?
Causes for this code may include:
Defective neutral safety or shift selector switch Shorted or open wiring or connectors in NEUTRAL input circuit Faulty PCM or a programming errorWhat are some P081D troubleshooting steps?
A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle specific diagnostic information will be required to diagnose a code P081D.
You may use your source of vehicle information to locate a technical service bulletin (TSB) that matches the vehicle year, make, and model; as well as the engine size, code/s stored, and symptoms exhibited. If you find one, it could yield helpful diagnostic information.
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 difficult 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.
Step 1
Use the DVOM to test 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 neutral safety/shift selector switches as required. Replace switches that do not test within system parameters.
Step 3
If system switches and circuits are functional, use the DVOM to test NEUTRAL input circuits to the PCM. Disconnect all controllers prior to using the DVOM for testing.
NEUTRAL input codes are most often attributed to neutral safety switch failureRead: 23
