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DTC codes / P06xx · Computer and output circuits / P0637

P0637Power Steering Control Circuit High

P0637 indicates that the power steering control module has detected an abnormally high voltage on its control circuit, which typically means the circuit is shorted to voltage or the module's internal driver has failed. The computer sets this code when the signal voltage on the steering control wire exceeds the expected range for a calibrated period.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • The power steering warning light illuminates on the dashboard.
  • Steering effort may increase noticeably, especially at low speeds or during parking maneuvers.
  • The steering system may default to a fail-safe mode with reduced or no power assist.
  • In some vehicles, a chime or message appears in the driver information center.
  • Often no symptoms besides the warning light, with steering feel unchanged.

Common causes, most likely first

  1. A short to voltage on the power steering control circuit wiring, often from chafed insulation or a pinched harness.
  2. A faulty power steering control module with an internal short in its driver circuit.
  3. Corroded or damaged connectors at the steering control module or the power steering motor.
  4. A failed power steering motor that back-feeds voltage into the control circuit.
  5. Water intrusion into the steering control module or connector causing a high-voltage signal.
  6. An intermittent short to voltage from aftermarket accessories or poor previous repairs.

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related codes in the power steering control module.
  2. Inspect the power steering control circuit wiring for signs of chafing, pinching, or contact with hot or moving components.
  3. Disconnect the power steering control module and the steering motor, then measure resistance and voltage on the control circuit to isolate a short to voltage.
  4. Check connectors for corrosion, water intrusion, or loose terminals, and clean or repair as needed.
  5. If the wiring and connectors are intact, test the power steering motor for internal faults that could back-feed voltage.
  6. Substitute a known-good power steering control module only after confirming the circuit is not shorted to voltage.
  7. Clear the code and perform a road test to verify the repair and ensure the code does not return.

When high voltage is not the module's fault

  • A short to voltage on the control circuit is more common than a failed control module, so always rule out wiring damage before replacing expensive parts.
  • The power steering control module often shares a ground with other chassis components; a poor ground can cause erratic voltage readings that mimic a high-voltage fault.
  • Aftermarket electrical accessories tapped into the steering circuit can introduce voltage spikes that set P0637 without any underlying component failure.
  • On some vehicles, a weak or failing battery can cause the power steering module to log this code due to unstable supply voltage, so check the charging system first.

Can I keep driving with P0637?

You can usually drive the vehicle, but expect heavier steering effort, especially at low speeds, and avoid high-speed maneuvers that require quick steering response. Have the fault diagnosed soon to prevent a sudden loss of power assist.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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