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 Subaru, BMW, Mazda, Volkswagen, Audi, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.
If your vehicle has stored a P081A code, it means that the Powertrain Control Module (PCM) has detected a higher than expected voltage level in the starter disable switch circuit. This type of code can be applicable to both manual and automatic transmission vehicles.
The starter disable switch is typically a single-circuit open/closed switch that interrupts voltage between the ignition switch and the starter solenoid if the clutch is not depressed, the (manual) transmission is not in neutral, or the (automatic) transmission is not in park. Vehicle applications with an automatic transmission may have the starter disable switch integrated into the neutral safety switch or the gear selector. The Transmission Control Module (TCM) or the PCM starter monitor deactivates the circuit voltage with the ignition in the ON position. The TCM can be a standalone module or part of the PCM.
If the PCM detects that the voltage in the starter disable switch circuit is not within the allowed parameters, a P081A code may be stored and a Malfunction Indicator Lamp (MIL) illuminated. Multiple ignition cycles (with a failure) may be required for the MIL to illuminate.
How Severe Is This DTC?
A stored P081A code may be accompanied by a no-start condition and also indicates that an electrical issue or mechanical failure has occurred. The conditions that contributed to the storage of a code of this nature should be rectified as soon as possible.
What Are Some of the Symptoms of the Code?
Symptoms of a P081A fault code may include:
Engine does not crank
Engine cranks with transmission in gear
No symptoms may be present
What Are Some of the Common Causes of the Code?
Causes
of this code may include:
Faulty starter disable switch
Shorted or open wiring or connectors in the starter disable switch circuit
Faulty PCM or programming error
What Are the P081A Troubleshooting Steps?
A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle-specific diagnostic information will be needed to diagnose a P081A 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 the engine size, stored codes, and presented symptoms. If you find one, it might provide helpful 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 drive 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 the code being stored may need to worsen before an accurate diagnosis can be made.
If the code immediately resets, the next step in your diagnosis will require you to search 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, ground, and signal output at the appropriate starter disable switch. Typical starter disable switch circuits consist of battery voltage (when activated) or ground (when deactivated).
Step 2
Use your vehicle diagnostic information source and the DVOM to test the starter disable switches, if necessary. Replace any switches that do not test within system parameters.
Step 3
If the system switches and circuits are functional, use the DVOM to test the starter disable switch circuits to the starter, as well as to the PCM. Disconnect all controllers before using the DVOM for testing.
Starter disable switch circuit codes are most often attributed to a switch failure
Manual transmission vehicles often use multiple starter disable switches (one for the clutch and another for neutral)