P0801 Reverse Inhibit Control Circuit Malfunction

Description and meaning of DTC p0801

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.

p0801 diagnostic trouble code symptoms

Symptoms of a P0801 trouble code may include:The shifter may go into reverse while the vehicle is moving forwardThe shifter may fail to go into reverseThere may be no symptoms exhibitedBlown fuses in transmission control related circuits

DTC p0801 - possible causes

Causes for this code may include:Defective reverse inhibit solenoidBad reverse inhibit sensorOpen or shorted reverse inhibit control circuitFaulty PCM or a programming error

How to fix OBD-II diagnostic trouble code p0801

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 1Use 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 2If 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 3Use 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 4If 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. Shifter linkage wear, shifter bushing wear, or shift pawl wear may contribute to reverse inhibit control failure

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