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Error Code P0815 is defined as Upshift Switch Circuit. Error Code P0815 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, Acura, Aston-Martin, Ford, Mercedes-Benz, and Vauxhall. Specifications on the definition, troubleshooting, and repairs, of course, vary between make, model, and powertrain configuration.
If the vehicle registers the Error CodeError Code P0815, this means the PCM (powertrain control module) has determined a malfunction in the upshift switch circuit. This code, however, is usually limited to paddle shifters vehicles.
The TCM (transmission control module) is sometimes a standalone unit. In recent years, however, it’s been commonly integrated into the single housing of the ECM (engine control module). This component is now referred to as the PCM. The upshift (paddle) shifter button is usually found in the steering wheel horn pad, close to the driver’s finger position. This is usually a type of sport shifter commonly found in high-performance vehicle models. To ensure continuity, the PCM monitors the transmission gear selection in comparison to the upshift switch input signal. Also, to ensure it stays within the established parameters, the PCM monitors the upshift switch circuit.
If the PCM detects a problem in the transmission gear selection (transmission gear selection is not the appropriate one to the selection signal input by the upshift switch, or if the switch circuit voltage is outside the allowable parameters, then the Error Code P0815 will be stored and simultaneously activate the Check Engine light. In some cases, multiple ignition cycles (with a failure) may be needed to activate the Check Engine light.
- Disabled manual (paddle) upshift function
- Shift indicator shows the wrong gear
In other cases, the vehicle may not show symptoms at all.
- Faulty upshift switch
- Short or open circuits in the upshift 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.
Test the voltage, ground, and signal output at the right upshift switch using the DVOM. Typically, the upshift switch circuits consist of either the battery voltage (when activated) or the ground (if deactivated).
If all the system circuits are working correctly, then test the upshift switch circuits to the PCM or the transmission using the DVOM. Make sure you disconnect all controllers before using the DVOM for testing.
Test the upshift switches using your source of vehicle diagnostic information and the DVOM. Switches that don’t test within the system’s specifications must be replaced.
How to Fix
- Replacement or reprogramming of PCM (rare)
- If the transmission mode selector fails, then replace the normal/performance switch, then retest the vehicle’s transmission control system.
Upshift switch codes are usually attributed to a switch failure.
This code indicates a serious electrical problem or mechanical failure, so it must be addressed as soon as possible.