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, Dodge, Buick, Cadillac, Peugeot, Chevrolet, Toyota, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.
If your vehicle has stored a P0801 code, it means that the powertrain control module (PCM) has detected a malfunction in the reverse inhibit control circuit. A P0801 may pertain to the transmission or transfer case, depending on the vehicle’s make and model.
The transmission control module (TCM) or transfer case control module (TCCM) may be a standalone unit but is most often integrated into a single housing with the engine control module (ECM). This is referred to as the PCM.
The PCM uses input signals from multiple engine and transmission sensors to calculate the automatic shift strategy. The reverse inhibit switch is designed to prevent the transmission from shifting into reverse while the vehicle is moving forward. Typically, an electronically controlled solenoid is responsible for actuating a piston that prevents the reverse shift lever pawl from engaging the reverse selector when the transmission is already engaged in a forward gear.
If the PCM detects a reverse inhibit circuit voltage level that exceeds the maximum allowable parameters, a P0801 code may be stored and a malfunction indicator lamp (MIL) illuminated.
How severe is this DTC?
The presence of a stored P0801 code indicates that the reverse inhibitor may be disabled. 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 P0801 trouble code may include:
The shift lever may engage reverse while the vehicle is moving forward
The shift lever may not engage reverse
There may be no symptoms
Blown fuses in transmission control-related circuits
What are some common causes of the code?
Causes
of this code may include:
Faulty reverse inhibit solenoid
Bad reverse inhibit sensor
Open or shorted reverse inhibit control circuit
Faulty PCM or programming error
What are the troubleshooting steps for P0801?
When diagnosing automatic transmission codes, you should start by ensuring the transmission fluid is clean and the transmission is filled to the appropriate level. If the fluid level is low, locate the source of the leak and repair the condition. Refill the transmission with the recommended fluid and proceed.
A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle-specific diagnostic information will be needed to diagnose a P0801 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.
With the transmission filled to the proper level with the recommended fluid, move on to the first step of diagnosis.
Step 1
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 this 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.
Step 2
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 3
Use the DVOM to test voltage and ground circuits at the reverse inhibit solenoid and sensor (if applicable). If voltage and ground are present, test the reverse inhibit solenoid and sensor according to manufacturer specifications. Any component not meeting recommended specifications should be considered faulty. If the components are functional, test the signal circuit that enters the PCM.
Step 4
If the reverse inhibit solenoid and sensor are functional and the signal input is present, use the DVOM to test the system circuits. The voltage drop testing method works well for this task. Disconnect all controllers from the circuit before testing resistance with the DVOM.
Worn shift linkage, worn shift fork, or worn control pawl can contribute to reverse control failure