FixItFor.Us
P codepowertrainMedium severity

P0637Power Steering Control Circuit High

The power steering control circuit voltage has risen above its expected range, usually from a short to battery voltage or an open with pull-up.

Definition

The PCM or power steering control module monitors the drive circuit for the electric power steering motor or variable-assist solenoid and compares actual circuit voltage to the commanded state. P0637 sets when the circuit reads higher than the calibrated maximum, typically caused by a short to battery voltage, a broken circuit on a system with an internal pull-up, or a failed module driver stuck open. Symptoms include a power steering warning lamp and steering assist that is disabled, reduced, or in some variable-assist systems stuck at one assist level regardless of speed. The fault is electrical; the mechanical steering connection is unaffected.

Common causes

  • Control circuit wiring shorted to battery voltage or an ignition feed
  • Open circuit read as high on systems with an internal pull-up voltage
  • Corroded connector adding resistance in the actuator return path
  • Failed EPS motor or solenoid with an internally open winding
  • Faulty driver transistor in the power steering control module or PCM

Common misdiagnoses

  • Replacing the power steering pump for an electrical circuit fault
  • Replacing the EPS motor when a harness wire is shorted to a 12-volt feed
  • Replacing the power steering pressure sensor instead of testing the control circuit
  • Replacing the battery or alternator for a localized circuit short

Troubleshooting steps

  1. 1.Measure the control circuit voltage against the commanded state

    With the ignition on, a circuit pinned at battery voltage while the scan tool commands a low or duty-cycled state confirms the high condition.

  2. 2.Check for a short to voltage

    Disconnect the module and actuator, turn the ignition on, and verify 0 volts on the control wire; any voltage present means the wire is contacting a powered circuit, often in a shared loom.

  3. 3.Test the actuator winding for an open

    Measure the EPS motor or solenoid coil resistance; an infinite reading lets pull-up voltage float the circuit high and condemns the actuator.

  4. 4.Inspect connectors for corrosion and added resistance

    Check the actuator and module connectors for green or white corrosion, and confirm less than 1 ohm through each terminal junction.

  5. 5.Confirm the module driver last

    With wiring and actuator verified good, a circuit the module cannot pull down indicates a failed internal driver; replace and program the module per service information.

Related codes