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P0635 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Definition

P0635 is an OBD-II Code that is set when the PCM (Powertrain Control Module) detects an issue with the Power Steering Control Circuit.

Meaning

A P0635 code is the result of the ECM (Engine Control Module) receiving a signal indicating a problem with the power steering control circuit. There are several components that are part of the power steering system including the power steering motor, ECM, PCM, ABS/TCS module, line pressure modulator valve, and high-pressure and low-pressure hoses.

Causes

Common causes for this code include:

  • Bad Power Steering Control Module
  • Faulty Power Steering Motor
  • Leak in Hydraulic System (Low or High Pressure)
  • Damaged, Worn, Loose Wire(s) to/from PCM (Powertrain Control Module)
  • Interior Leaks
  • External Leaks 
  • Kinked or Blocked Hoses 
  • Open or Short in Sensors and Lines 
  • Loose Fitting Connectors (Lose Bolts & Nuts on Valve Assembly, Improperly Installed Valve Assembly, Damaged PCM Sensor, Cable Harness Connection)

Symptoms

Symptoms of P0635 can include any or all of the following:

  • Check Engine Light illumination
  • Noise from P/S pump or steering system
  • Loss of hydraulic fluid from reservoir
  • Audible chime
  • Decrease in power-assist when turning the steering wheel 
  • Noticeable lack of power assist when turning the steering wheel 
  • Abnormally stiff steering effort while driving
  • Abnormality in Steering Feeling while driving

Diagnosis

To diagnose a P0635 DTC code, an automotive technician would:

1. Check the power steering fluid level. If it is low, top off and continue with diagnosis.

2. Inspect the condition of all related components, including cables, lines/hoses, reservoir bag, power steering pump pulley/assembly, belt tensioner assembly (if present), etc.

3. Check for external leaks at the pressure control switch/pulsation dampener assembly under the vehicle near or on the brake fluid reservoir 

4. Check for interior leaks by checking high-pressure hydraulic hoses for small splits in them 

5. Check for short to voltage at both ends of lines from power steering pressure switch / pulsation dampener assembly to PCM 

6. Use a scan tool to view live data while turning the steering wheel, and check pressure to power steering control module 

7. Check for low or high pressure in hydraulic system (high-pressure side is typically used for data) 

8. Reset DTCs and road test vehicle to recheck problem 

9. If all parameters are within specs, there could be a loose cable or connection at the steering rack, PCM/ECM, power steering control module, ABS system, brake pedal position sensor assembly, etc

Common mistakes

The following are common mistakes when diagnosing the trouble code P0635:

  • Failed to check the fluid level before assuming there is a power steering fluid leak
  • Failed to inspect closely for small leaks, which may be difficult to locate 
  • Checked short circuits but missed open circuits when checking resistance in wires and connectors 
  • Did not use a scan tool to recheck trouble codes after resetting them with a scan tool 
  • Did not properly interpret data when checking pressure across hydraulic system lines

How serious is this?

A car with a P0635 trouble code would be drivable, but the steering would feel stiff and make a noise if it is failing. It may also suffer from no power assist when turning the wheel. 

If this code comes up when starting your car, make sure to have it towed in for repair as soon as possible because without power-assist, you won't be able to steer or brake properly. If left unattended, severe damage could occur to internal components of the hydraulic system. 

Even if your car is still drivable, poor steering may put you and other drivers at risk on the road. As a result, a P0635 fault should be addressed as soon as possible.

What repairs can fix the code?

The following are solutions that may fix this problem:

  • Inspect all related components for damage 
  • In the event of a power steering pump failure, replace it 
  • Replace damaged or leaking high-pressure lines and hoses to/from steering rack assembly 
  • Inspect PCM sensor harness connector and wiring for open circuits, short circuits, and loose connections 
  • Repair short to voltage in wires from power steering pressure switch/pulsation dampener assembly to PCM 
  • Remove kinked or blocked hoses or external leaks from under vehicle near brake fluid reservoir 
  • Replace PCM if any other problem is found beyond the scope of these checks.

Related codes

A P0635 is related to and may be accompanied by the following codes: 

  • P0641: High-Pressure PS Pump Error 
  • P0614 – Abnormal operation of electric power steering control module or PCM 
  • P0605 – Abnormal operation of power steering control module 

How much does it cost to fix the P0635 code?

The repair cost of a P0635 code depends on the extent of the problem and who fixes it. The average cost for a P0635 repair is between $100-$200. 

For a high-end estimate, an automotive service professional may charge around $200-300 to diagnose and repair a power steering system with this code or other problems that are related.

Conclusion

In conclusion, the P0635 is a trouble code that is related to power steering pressure switch/pulsation dampener assembly. 

If you are having stiff or difficult steering while driving, be sure to have your car towed in for repair as soon as possible because it can become dangerous without power assist. If left unattended, severe damage could occur to internal components of the hydraulic system. 

Even if your car is still drivable, poor steering may put you and other drivers at risk on the road. As a result, a P0635 fault should be addressed as soon as possible - the cost of repairing the code depends on where you go for service and how extensive the damage is.

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