P0929 code definition
The P0929 code 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 with the gear shift lock solenoid circuit.
What the P0929 code means
A vehicle with an automatic transmission uses the gear shift lock solenoid to ensure that your vehicle cannot be shifted out of “Park” without the brake pedal being depressed. When the vehicle engine is “on” and the brake pedal is fully depressed, the gear 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 gear shift lock solenoid, a code P0929 can be stored.
What causes the P0929 code?
Several problems may cause a P0929 code including:
- Low transmission fluid
- Dirty transmission fluid
- Low battery voltage
- Damaged or corroded electrical wiring to or from the gear shift lock solenoid
- Damaged or defective gear shift lock solenoid
- Damaged or defective brake light switch
- Damaged or defective ECM (rare)
What are the symptoms of the P0929 code?
Symptoms of a P0929 code may include:
How does a mechanic diagnose the P0929 code?
A mechanic may use several methods to diagnose a P0929 trouble code, including:
- Utilize an OBD-II scanner to check for a stored P0929 trouble code
- Check transmission fluid level
- Check transmission fluid quality
- If transmission fluid is dirty, check transmission pan for signs of clutch debris or other contaminants
- Check battery voltage/charge
- Visually inspect the wiring and electrical system for any obvious signs or damage or wear
- Check for any blown fuses
- Test gear shift lock solenoid for continuity
- Test brake light switch for continuity
Common mistakes when diagnosing the P0929 code
One common cause of a P0929 trouble code is a faulty brake light switch, which will not allow the vehicle to move out of park. The fuse that controls the brake light switch and shift lock may have blown, and should be diagnosed before performing further repairs or replacements.
How serious is the P0929 code?
Because a vehicle’s safe driving operation most likely will be impacted due to faults that store a P0929 code, this code is considered a potentially serious code. When this code appears, it is recommended to immediately take your vehicle to your local service center or mechanic for repair and diagnosis.
What repairs can fix the P0929 code?
Several repairs can fix a P0929 trouble code and include:
- Fill the transmission fluid to manufacturer recommended levels
- Change the transmission fluid (if necessary)
- Charge or replace the vehicle’s battery
- Replace any damaged or blown fuses
- Repair or replace damaged or defective brake light switch
- Repair or replace damaged or defective gear shift interlock solenoid
- Clear all codes, test-drive the vehicle, and rescan to see if any codes reappear
Additional comments related to a P0929 code
Note, an automatic transmission will have a “shift lock” feature, which can allow the drive to temporarily bypass a locked gear shift solenoid, and allow you to shift into drive to move your vehicle to a mechanic or out of a potentially dangerous location.
Need help with a P0929 code?
YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.
This article originally appeared on YourMechanic.com as P0929 OBD-II Trouble Code: Gear Shift Lock Solenoid Circuit Range/Performance and was authored by Parker Hill.