Concerns the drive circuit that moves the shift mechanism of an automated manual gearbox in the forward shift direction. Depending on design this is one of two solenoid valves on a double-acting shift cylinder or one rotation direction of an electric shift motor. The code sets when the module finds this output open or electrically faulty, e.g. no current while the driver is on. No manufacturer documents the code publicly. A ZF patent feeds each chamber of a double-acting cylinder through its own 3/2 solenoid valve, an Isuzu patent turns the shift motor forward or reverse by shift direction. CARB requires circuit checks on outputs. P0921 to P0923 are the siblings, P0924 the reverse direction. Gears in this direction can no longer be engaged.
Medium severity. Can I keep driving?Drive as little as possible and gently. If the transmission slips or stays in one gear, go slowly to a repair shop or call for a tow truck.
Symptoms
- Transmission warning light on
- Some gears cannot be selected, the gearbox skips them or stays in neutral
- Vehicle may only move off in a limited set of gears
Most likely causes
- Loose, corroded or unplugged connector at the shift actuator or valve
- Broken drive wire between module and actuator
- Open solenoid coil or motor winding in the actuator
- Faulty driver stage in the transmission control module
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
- It can trigger limp mode.
- It affects emissions.
What each character of P0920 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 9: Transmission
- 20: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0920?
Drive as little as possible and gently. If the transmission slips or stays in one gear, go slowly to a repair shop or call for a tow truck.
What causes code P0920?
The most common causes are: loose, corroded or unplugged connector at the shift actuator or valve; broken drive wire between module and actuator; open solenoid coil or motor winding in the actuator.
Related codes
- P0921Gear Shift Forward Actuator Circuit Range/Performance
- P0922Gear Shift Forward Actuator Circuit Low
- P0923Gear Shift Forward Actuator Circuit High
- P0924Gear Shift Reverse Actuator Circuit/Open
- P0910Gate Select Actuator Circuit/Open
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.