Error Code P0635 is defined as Power Steering Control Circuit, meaning there’s a problem in the power steering control circuit, often caused by defective steering position, broken wiring, or pressure switch.

This code is a generic trouble code, which means it applies to all vehicles equipped with OBD-II system, especially those made since 1996 up to present. This includes vehicles from, but not limited to, Dodge, Ford, Mercedes Benz, Renault, Saturn, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.

When the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) sees a malfunction within the power steering control circuit, it will register the Error Code P0635 and activate the Check Engine light.

The job of the power steering control circuit is to provide the right voltage for various power steering components. The PCM oversees the voltage signals from the power steering controller, switches, and sensors. These components provide the proper fluid pressure within the power steering system. This is a very important process in preventing damage to the power steering components. The power steering control circuit facilitates the power steering system to adapt to the different driving conditions and prevent erratic or stiff steering. Also, this system alerts the PCM for possible issues to get immediate attention.

Other associated power steering control circuit codes include:

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  • Error Code P0636
  • Error Code P0637

Common Symptoms

  • Erratic or stiff steering
  • Noise while turning

Possible Causes

In most cases, this problem is caused by a defective steering position or pressure switch. Though switches can account for the majority of this code, faulty, broken, and corroded wires related to the control modules can lead to this kind of problem as well. Other common causes include:

  • Faulty power steering pressure switch
  • Faulty power steering position switch
  • Defective steering wheel
  • Broken ground wire
  • Loose control module ground strap
  • Leak or insufficient fluid level
  • Blown fuse or fuse-able link
  • Defective PCM

How to Check

The first thing that must be done to diagnose this code properly is to check the TSB (technical service bulleting) for the specific vehicle year, model, and power plant. This usually points to the right direction of diagnosis.

Next step is to check the power steering fluid level and look for signs of possible leaks that could be causing a negative effect on the pressure supplied to the power steering controller and its associated components. Proper fluid pressure plays an important role in the function of the circuit.

Look for the components within the circuit and conduct a thorough visual inspection to check the associated wiring for obvious signs of damage, such as burnt spots, bare wires, rubbing, scraping. Then, check the connectors for security, corrosion, and damages on the pins.

Also, check the power steering controller, switches, associated sensors, and the PCM. The conditions of CAN (controller area network) is also important for the troubleshooting process, as a damaged wiring harness makes it difficult to pinpoint the defective components.

Advanced Steps

Advanced steps for diagnosis vary from one vehicle to another and may require specific advanced equipment and tools, such as a digital multi-meter, and specific technical references for the vehicle. Voltage requirements also vary based on the specific year and model of the vehicle.

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Voltage Checks

Battery voltage should be around 12V, and the starter should have battery voltage with the ignition switch in the start position. The presence of voltage with the starter not engaging is a sign of a defective starter or starter solenoid. The lack of voltage means the ignition switch is faulty, or there’s a problem in the wiring.

If this process determines the absence of a power source or ground, then perform a continuity test to check the integrity of the wiring, ignition switch, and other components. Continuity test must be performed with the power removed from the circuit while reading for wiring and connections must be at 0 ohms of resistance, unless otherwise specified in the technical data of the vehicle. Resistance or no continuity means there’s a faulty wiring problem (open or short) and must be repaired or replaced.

How to Fix

Depending on the diagnosis, common repairs for this code include:

  • Replacement of the power steering pressure switch
  • Replacement of the power steering position switch
  • Repair of power steering link
  • Cleaning off corrosion from the connectors
  • Replacement of blown fuse or fuse-able link (if applicable)
  • Repair or replacement of faulty wiring
  • Replacement of power steering controller
  • Flashing or reflashing of PCM

Error Code P0635 often prevents a control module from communicating properly, which may cause other trouble codes. CAN issues can be tricky to solve, which may lead to misdiagnosis in some circumstances; thus, if there are other trouble codes present, it’s important to focus on those that pertain to the CAN before tending to component-related issues.

You can use a specialized scanner (i.e., Autohex) to pinpoint control module problems more accurately and quickly.