Error Code P081D is defined as Neutral Input Circuit. Error Code P081D 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, Jaguar, Land Rover, Mini, and Volvo. Specifications on the definition, troubleshooting, and repairs, of course, vary between make, model, and powertrain configuration.

If the Error Code P081D stores in the vehicle, which means the PCM (powertrain control module) has determined a malfunction in the neutral input circuit of the neutral safety switch (also known as shift selector switch). This code only applies to vehicles with automatic transmission.

The neutral input circuit is usually integrated into the neutral safety switch or shift selector switch. If the transmission is placed in neutral, a voltage signal is sent into the (TCM) transmission control module or the PCM. The controller also monitors the circuit voltage each time the ignition is at the ON position. The TCM can be a standalone module or part of the PCM.

If the PCM is unable to detect a right degree of voltage in the neutral circuit, with the transmission apparently in the park or neutral position, then this error code will be stored, along with the activation of the MIL (malfunction indicator lamp). In some cases, multiple failure cycles may be needed to activate the MIL.

Common Symptoms

  • Engine no start condition
  • The engine starts with the transmission in gear

In other cases, the problem may not exhibit any symptoms at all.

Possible Causes

  • Defective neutral safety or shift selector switch
  • Shorted or open wiring in the connectors or neutral input circuit
  • Defective or programming error in 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 really 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 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.

First Step

Using the DVOM, test the neutral input voltage at the appropriate neutral position/shift selector switch. Usually, the Neutral input circuit consists of either the battery voltage (activated) or ground (deactivated).

Second Step

Using the vehicle diagnostic information and the DVOM, test the neutral safety/shift selector switches as needed. Switches that don’t test within the system parameters must be removed and replaced.

Third Step

If the circuits and system switches are in working condition, then test the neutral input circuits to the PCM using the DVOM. Make sure you disconnect all controllers before using the DVOM for testing.

How to Fix

  • Repair or replacement of neutral safety switch or shift selector switch
  • Repair or replacement of shorted or open wiring or connector neutral input circuit
  • Defective or programming error in the PCM

neutral input codes are usually related to neutral safety switch failure.

This error code is usually accompanied with a no-start condition, which indicates that the problem is either an electrical problem or mechanical failure. Conditions like this must be addressed as soon as possible.