P0635Generic code

P0635 Code: Power Steering Control Circuit

The P0635 code means the computer found an electrical fault in the power steering control circuit. It can cause heavy steering or the loss of variable assist. Check the fuse, relay, connector and wiring before you replace the component.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$50 to $900
Difficulty
Medium
System
Chassis, Brakes and Suspension
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0635 code means

On some vehicles the computer controls a valve or a motor that adjusts the steering assist according to speed: more help when parking and less on the highway.

The computer watches the control circuit from its own driver transistor. The P0635 code flags an electrical fault in that control circuit. Before you replace the component, check the fuse, relay, connector and wiring, which are the most common causes.

If the circuit fails, the steering usually ends up with a fixed level of assist (heavy during maneuvers or too light on the highway). On electric power steering, the fault can switch the assist off, and the steering wheel becomes very heavy.

Always start with the simplest checks: fuse, relay and connector. Then check power, ground and signal with the component connected (using back-probes) and, last, the continuity of each wire to the computer. Replace the component only when all of that checks out.

P0635 code symptoms

  • Check engine light or another warning light on.
  • Heavy steering, or no variable assist.
  • Steering is heavy when parking.
  • Steering is too light at high speed.
  • Steering warning light on.

Likely causes of the P0635 code

  1. Damaged connector. Loose, broken or corroded.
  2. Blown or defective fuse or relay.
  3. Wiring cut or shorted between the component and the computer.
  4. Failed component. The coil, the motor or the internal electronics.

How to diagnose the P0635 code step by step

  1. Activate the component with the scan tool and check whether it responds.
  2. Check the fuse and relay. Measure the voltage on both sides of the fuse, and swap the relay with an identical one.
  3. Measure the supply at the connector. You should see battery voltage with the key on or when the component is activated.
  4. Measure the resistance of the component and compare it with the manual. Also check the insulation to ground.
  5. Check the control wire for continuity to the computer and for shorts.

How to fix the P0635 code

  • Repair the connector, the wiring or the power supply.
  • Replace the power steering control if it does not respond even with correct power and command signals.
  • Clear the codes and verify the repair.

Technical reference data

  • The control valve is driven by a PWM signal, or it is an electric motor, depending on the system.
  • Reference values: check the manufacturer data for your vehicle.

Brand-specific notes

This code shows up on a few steering designs, so know which type your vehicle has before you start testing.

P0635 on GM

It appears on GM vehicles with variable assist steering.

P0635 on Electrohydraulic Steering

It also appears on some vehicles that have electrohydraulic power steering.

Frequently asked questions about P0635

Can I drive with a P0635 code?
With caution. Heavier steering takes more effort, especially when maneuvering, so be careful at low speed and when parking.
What does the power steering control do?
On some vehicles the computer controls a valve or a motor that adjusts the steering assist by speed. You get more help when parking and less on the highway.
Do I always have to replace the part?
No. Check the fuses, relays, connectors and wiring first, because they are the most common cause.
How much does it cost to fix P0635?
As a rough guide, between $50 and $900. A fuse or connector repair is at the low end, and replacing the control component is at the high end.
What does the P0635 code mean?
It is a generic OBD2 code that means the computer found an electrical fault in the power steering control circuit.
What is the most common cause of P0635?
For a P0635 code, the usual culprit is a damaged connector, a blown fuse or a faulty relay. Check those and the wiring before you suspect the component itself.

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