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P090AClutch "B" Actuator Control Circuit/Open

The control circuit for the clutch "B" actuator is open or has a general electrical fault, so the module cannot command the second clutch.

Definition

On dual-clutch and automated manual transmissions the TCM drives an electromechanical or electrohydraulic actuator to apply and release each clutch; this code covers the "B" (second) clutch actuator. P090A sets when the TCM detects an open circuit or general fault on the actuator control circuit — for example, no current flow when the driver is commanded on. With the actuator inoperative the affected clutch cannot be controlled, producing missing gears (often every other ratio on a DCT), harsh engagement, limp-home operation, or a complete no-drive condition, along with a transmission warning lamp and stored MIL.

Common causes

  • Open winding in the clutch actuator motor or solenoid
  • Broken wire or open in the actuator control harness
  • Corroded, burned, or backed-out connector terminal
  • Blown fuse or open power feed to the actuator circuit
  • Failed TCM/mechatronic output driver
  • Actuator connector left unplugged after service

Common misdiagnoses

  • Replacing the clutch assembly when the actuator circuit is at fault
  • Replacing the entire transmission for a no-drive complaint
  • Replacing the actuator when a harness open is the cause
  • Replacing the battery or shifter module

Troubleshooting steps

  1. 1.Check for companion codes and actuator function

    Scan all modules and use bidirectional controls if available to command the clutch "B" actuator; no movement, sound, or current draw supports an open circuit.

  2. 2.Verify power and fuses

    Check the actuator/mechatronic supply fuse and relay, and confirm battery voltage on the power feed at the actuator connector with the key on.

  3. 3.Measure actuator resistance

    Unplug the actuator and measure the motor or solenoid winding resistance against the service specification (commonly single-digit ohms for a motor); an open (OL) reading condemns the actuator.

  4. 4.Check harness continuity

    With the TCM and actuator disconnected, verify near-zero resistance end-to-end on each control wire and no shorts between wires, flexing the harness while measuring.

  5. 5.Inspect the connectors

    Look for burned or heat-discolored terminals at the actuator — these circuits carry meaningful current and overheated crimps are a common failure point.

  6. 6.Confirm module output last

    Only after wiring and actuator prove good, test for the TCM's switched output at the connector while commanding the actuator; a missing drive signal points to the module or its calibration.

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