P2791

Gate Select Direction Circuit Low

P2791 is a generic OBD-II powertrain diagnostic trouble code: Gate Select Direction Circuit Low. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P2791
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P2791 means

P2791 is the circuit-low variant of the gate select direction fault. The transmission control module detects that the voltage on the gate select direction control circuit is below the acceptable operating range when the circuit is commanded active. This indicates a short to ground, a shorted actuator winding, or a fault in the TCM driver that pulls the circuit output abnormally low.

The gate select direction circuit typically operates as a bridge or H-bridge output to a DC motor or directional solenoid that moves the gear selector laterally across the shift gate in automated manual or robotised transmissions. A low-circuit condition may prevent the actuator from generating enough force to complete a lateral gate movement.

Diagnosis begins with visual inspection of the wiring harness and connector for damage, followed by resistance measurement of the actuator and continuity checks for shorts to ground. If the circuit and actuator measure within specification, a faulty TCM output stage is the remaining possibility.

Common causes

Most-frequently reported root causes when P2791 is logged.

  • 1
    Short to ground on the gate select direction control wire.
  • 2
    Internally shorted gate select actuator coil or motor winding.
  • 3
    Chafed wiring harness causing intermittent or permanent ground fault.
  • 4
    Damaged connector causing pin-to-pin short.
  • 5
    Failed TCM gate select direction driver stage.
  • 6
    Moisture ingress into the gearbox connector causing tracking short.
  • 7
    Improper wiring repair creating an unintended ground path.

Symptoms drivers notice

MIL or gearbox warning light illuminated.
Gate select actuator not responding to commands.
Transmission unable to perform lateral gate moves, preventing gear changes.
Gearbox defaulting to neutral hold.
Possible abnormal heat at the TCM connector if the short draws significant current.

How to diagnose P2791

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and retrieve all stored and pending DTCs.
  2. 2
    Inspect the transmission harness and connector for shorts to ground, chafing, or moisture damage.
  3. 3
    Measure resistance of the gate select actuator at the transmission connector.
  4. 4
    With the TCM connector unplugged, verify no short to ground exists on the direction control circuit.
  5. 5
    Command the actuator via bidirectional scan tool controls and observe whether the fault returns immediately.
  6. 6
    If the circuit tests normal externally, evaluate TCM integrity by performing a TCM power and ground check.
  7. 7
    Replace the actuator or repair the wiring as indicated; replace the TCM only after all external causes are eliminated.

Related powertrain codes

Frequently asked questions

Is P2791 different from P2790?

Yes. P2790 is a general gate select direction circuit fault, while P2791 specifically identifies a low-voltage or short-to-ground condition on that circuit.

Can P2791 be caused by water damage?

Yes. Moisture ingression into the transmission connector or gearbox electrical housing is a known cause of low-circuit faults due to current tracking.

Will the transmission shift at all with P2791 active?

If the gate select cannot move laterally, the gearbox may be unable to change between gear planes, effectively preventing normal operation.

How do I locate the gate select actuator?

Consult the vehicle-specific service manual; the actuator is typically mounted on the outside of the transmission case or inside the mechatronic unit, depending on the design.

Disabling P2791 in software

RaceTune can permanently disable P2791 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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