Error Code P081B is defined as Starter Disable Circuit High. Error Code P081B 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, Audi, BMW, Mazda, Subaru, and Volkswagen. Specifications on the definition, troubleshooting, and repairs, of course, vary between make, model, and powertrain configuration.

If the vehicle stores the Error Code P081B, this means the PCM (powertrain control module) has determined a degree voltage that is lower than expected in the starter disable switch circuit. This code applies to both manual and automatic transmission vehicles.

Traditionally, the starter disable switch is a single circuit, open/closed switch that interrupts voltage between the ignition switch and the starter solenoid if the clutch isn’t depressed, the transmission (manual) is not in neutral, or the transmission (automatic) isn’t in the park position. Vehicles with an automatic transmission may have the starter disable switch integrated into the neutral safety switch or shift selector switch. The TCM (transmission control module, which can be a standalone module or part of the PCM) or the PCM monitors the starter disable circuit voltage with the ignition in the ON position.

If the PCM determines that the starter disable switch circuit voltage is outside the allowable parameters, then this error code will be set, 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

  • Faulty starter disable switch
  • Shorted or open wiring or connector in starter disable switch 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 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

Test the voltage, ground, and signal output at the appropriate starter disable switch using the DVOM. Typically, the starter disable switch circuits consist of either battery voltage (activated) or ground (deactivated).

Second Step

Next, use the vehicle source’s diagnostic information and the DVOM to test the starter disable switch as needed. Switches that don’t test within the system parameters must be removed and replaced.

Third Step

If the system switches and circuits are operational, then test the starter disable switch circuits to the starter and the PCM using the DVOM. Make sure you disconnect all controllers before using the DVOM for testing.

How to Fix

  • Replacement of starter disable switch
  • Repair or replacement of shorted or open wiring or connector in starter disable switch circuit
  • Defective or programming error in the PCM

Starter disable switch circuit codes are usually attributed to switch failure.

Vehicles with manual transmission often use multiple starter disable switches, one for clutch, and the other for neutral.