Powertrain, generic · Transmission

P0920 Gear Shift Forward Actuator Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

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

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

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–2,000
Time0.5–5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

gear shift forward actuatorwiring harnesstcm

Related codes

P0921P0922P0923P0924P0910

References: law.cornell.edu, patents.google.com, patents.google.com.