P0801 Reverse Inhibit Control Circuit Malfunction
OBD-II Trouble Code Technical Description
Reverse Inhibit Control Circuit Malfunction
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code and applies to many OBD-II vehicles (1996-newer). That 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 year, make, model and powertrain configuration.
If your vehicle has stored a code P0801, it means that the powertrain control module (PCM) has detected a malfunction in the reverse inhibit control circuit. A P0801 may pertain to either the transmission or transfer case, depending upon vehicle make and model.
The transmission control module (TCM) or transfer case control module (TSCM) may be a stand alone unit but is most commonly integrated into a single housing with the engine control module (ECM). This is called the PCM.
The PCM utilizes input signals from multiple engine and transmission sensors to calculate automatic transmission shift strategy. The reverse inhibit switch is designed to prevent the transmission from being shifted into reverse while the vehicle is proceeding in a forward direction. Typically, an electronically controlled solenoid is responsible for actuation of a plunger that prevents the reverse shifter pawl from engaging the reverse gear selector when the transmission is already engaged in a forward gear.
If the PCM detects a level of reverse inhibit circuit voltage that exceeds maximum allowable parameters, a code P0801 may be stored and a malfunction indicator lamp (MIL) illuminated.
What is the severity of this DTC?
The presence of a stored code P0801 indicates that the reverse inhibitor may be disabled. Conditions which have contributed to a code of this nature being stored should be rectified as quickly as possible.
What are some of the symptoms of the code?
Symptoms of a P0801 trouble code may include:
What are some of the common causes of the code?
Causes for this code may include:
What are some P0801 troubleshooting steps?
When diagnosing automatic transmission codes, you should begin by making sure that the transmission fluid is clean and that the transmission if 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 required to diagnose a code P0801.
You may use your source of vehicle information to locate a technical service bulletin (TSB) that matches the vehicle year, make, and model; as well as the engine size, code/s stored, and symptoms exhibited. If you find one, it could yield helpful diagnostic information.
With the transmission filled to the appropriate level with the recommended fluid, proceed with the first step of the diagnosis.
Step 1
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.
Step 2
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.
Step 3
Use the DVOM to test voltage and ground circuits at the reverse inhibit solenoid and sensor (if equipped). If voltage and ground are detected, test the reverse inhibit solenoid and the sensor according to manufacturer’s specifications. Any components which fail to comply with recommended specifications should be considered defective. If the components are functional test the signal circuit that is input to the PCM.
Step 4
If the reverse inhibit solenoid and sensor are functional, and the signal input is present, use the DVOM to test system circuits. The voltage drop testing method works well for this task. Disconnect all controllers from the circuit prior to testing resistance with the DVOM.
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"Delete Error Code Permanently, Disable DTC Error Code Function for p0801 in the ECU"
In extreme cases, we even have the option to permanently remove the specific DTC p0801 and disable the function of the specific error code in the ECU. All other fault code functions will then continue to work to protect the engine. This is different from clearing an error code with a diagnostic device. We have the option to permanently remove the function of the specific error code, so that it never comes back. Also emergency running that occurs on the specific error code can be solved in most cases.
Of course we prefer to first try to solve the cause of the error code, but sometimes the only solution is to permanently disable the DTC function of p0801.
