Definition of Code P0929
Code P0929 is a generic powertrain code related to the transmission, including pressure faults and sensor failures. In this case, the transmission control module has detected a fault in the shift lock solenoid circuit.
What does code P0929 mean?
A vehicle with an automatic transmission uses the shift lock solenoid to ensure that your vehicle cannot be moved out of “Park” without the brake pedal being pressed. When the vehicle’s engine is “on” and the brake pedal is fully depressed, the shift lock solenoid allows the vehicle to shift from “Park” to “Reverse” or “Drive”.
When the engine control module (ECM) detects an abnormal voltage reading or signal from the shift lock solenoid, a code P0929 may be stored.
What causes code P0929?
Several issues can cause a code P0929, including:
- Low transmission fluid
- Dirty transmission fluid
- Low battery voltage
- Damaged or corroded electrical wiring to or from the shift lock solenoid
- Damaged or faulty shift lock solenoid
- Damaged or faulty brake light switch
- Damaged or faulty ECM (rare)
What are the symptoms of code P0929?
Symptoms of a code P0929 may include:
- Check engine or warning light may illuminate
- The vehicle will not shift out of park
How does a mechanic diagnose code P0929?
A mechanic may use several methods to diagnose a P0929 fault code, including:
- Using an OBD-II scanner to check for a stored P0929 fault code
- Checking the transmission fluid level
- Checking the quality of the transmission fluid
- If the transmission fluid is dirty, check the transmission pan for signs of clutch debris or other contaminants
- Checking battery voltage/charge
- Visually inspecting wiring and the electrical system for any obvious signs of damage or wear
- Checking for blown fuses
- Testing the shift lock solenoid for continuity
- Testing the brake light switch for continuity
Common mistakes when diagnosing code P0929
A common cause of a P0929 fault code is a faulty brake light switch, which will not allow the vehicle to shift out of park. The fuse that controls the brake light switch and shift lock may have blown and should be diagnosed before performing any further repairs or replacements.
How severe is code P0929?
Since safely operating a vehicle will most likely be affected due to faults that store a P0929 code, this code is considered a potentially serious one. When this code appears, it is recommended to bring your vehicle to your local service center or a mechanic immediately for repair and diagnosis.
What repairs can fix code P0929?
Several repairs can correct a P0929 fault code and include:
- Fill transmission fluid to manufacturer-recommended levels
- Change transmission fluid (if necessary)
- Charge or replace the vehicle battery
- Replace any damaged or blown fuses
- Repair or replace the damaged or faulty brake light switch
- Repair or replace the damaged or faulty shift lock solenoid
- Clear all codes, test the vehicle, and rescan to see if any codes reappear