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 Ford, Acura, Vauxhall, Aston-Martin, Mercedes-Benz, Sprinter, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.
If your vehicle has stored a P0815 code, it means that the Powertrain Control Module (PCM) has detected a malfunction in the shift switch circuit. This type of code is typically limited to vehicles equipped with paddle shifters.
The Transmission Control Module (TCM) may be a standalone module or part of the PCM. The shift buttons (paddles) are usually located on the steering wheel horn pad near the driver’s finger position. They are used as a type of sport shifter, typically in high-performance models. The PCM monitors the transmission gear selection against the shift switch input signals to ensure continuity. Additionally, the PCM monitors the voltage of the shift switch circuit to ensure it is within established parameters.
If the PCM detects that the transmission gear selection does not match the gear selection signal input from the shift switch, or if the switching circuit voltage is not within allowed parameters, a P0815 code may be stored and a Malfunction Indicator Lamp (MIL) illuminated. Several ignition cycles (with a failure) may be required for MIL illumination.
How severe is this DTC?
A stored P0815 code indicates that a serious electrical problem or mechanical failure type has occurred. In any case, 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 P0815 fault code may include:
Manual gear shift function (paddle) disabled
Gear shift indicator displays incorrect gear
No symptoms may be apparent
What are some common causes of the code?
Causes
of this code may include:
Faulty gear shift switch
Short or open circuits in the shift switch circuit
Faulty PCM or programming error
What are the P0815 troubleshooting steps?
A diagnostic scanner, digital volt/ohmmeter (DVOM), and a source of vehicle-specific diagnostic information will be needed to diagnose a P0815 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 engine size, stored codes, and presented symptoms. If you find one, it may provide useful diagnostic information.
Use the scanner (connected to the vehicle’s diagnostic connector) to retrieve all stored codes and relevant freeze frame data. It’s 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 storage 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 consult 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 voltage, ground, and signal output at the appropriate shift switch. Typical gear shift switching circuits consist of battery voltage (when activated) or ground (when deactivated).
Step 2
If the system circuits are functional, use the DVOM to test the gear shift switching circuits to the PCM or transmission. Disconnect all controllers before using the DVOM for testing.
Step 3
Use your vehicle diagnostic information source and DVOM to test shift switches as needed. Replace switches that do not test within system specifications.
Shift codes are most often attributed to switch failure