Technical Description of OBD-II Trouble Code
High Circuit for Starter Disable
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to many OBD-II vehicles (1996-newer). This includes vehicles from Subaru, BMW, Mazda, Volkswagen, Audi, and others. While it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
If your vehicle has stored a code P081B, it means that the powertrain control module (PCM) has detected a lower than expected voltage in the starter disable switch circuit. This code can apply to vehicles with manual or automatic transmissions.
The starter disable switch is typically a single circuit, open/closed switch that interrupts the voltage between the ignition switch and the starter solenoid if certain conditions are not met. These conditions include the clutch not being depressed (for manual transmissions), the transmission not being in neutral (for manual transmissions), or the transmission not being in park (for automatic transmissions). Vehicles with automatic transmissions may have the starter disable switch integrated into the neutral safety switch or shift selector switch. The transmission control module (TCM) or PCM monitors the voltage of the starter disable circuit when the ignition is in the ON position. The TCM may be a standalone module or part of the PCM.
If the PCM detects that the voltage of the starter disable switch circuit is outside of the allowable parameters, it may store a code P081B and illuminate the malfunction indicator lamp (MIL). Multiple ignition cycles with a failure may be necessary for the MIL to illuminate.
What is the severity of this DTC?
A stored code P081B could result in a no-start condition and indicates that there has been an electrical issue or 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 P081B trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P081B troubleshooting steps?
To diagnose a code P081B, 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 year, make, and model of your vehicle, as well as the stored codes 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 time, the code is intermittent and may be more difficult to diagnose. In this case, 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 voltage, ground, and signal output at the appropriate starter disable switch. Typical starter disable switch 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 starter disable switches as necessary. 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 starter disable switch circuits to the starter and to the PCM. Disconnect all controllers before using the DVOM for testing.
