Power Steering Control Circuit High
P0637 indicates the power steering control circuit is reading a voltage signal higher than expected by the PCM. This typically occurs when the power steering pressure switch, position switch, or related wiring sends an abnormally high electrical signal to the engine control module.
What You Might Notice
- Stiff or difficult steering response
- Erratic or inconsistent steering behavior
- Check engine light illuminated
- Power steering noise while turning
- Reduced power steering assist
Most Common Causes
- 1
Defective power steering pressure switch
The pressure switch may be failing or stuck in a high-voltage state, causing it to report incorrect pressure readings to the PCM.
- 2
Faulty power steering position switch
The position switch detects steering wheel movement and can malfunction, sending erratic high-voltage signals to the control module.
- 3
Corroded or damaged wiring and connectors
Oxidation or physical damage to power steering circuit wiring or connectors can cause resistance issues that result in abnormally high voltage readings.
- 4
Loose ground strap or broken ground wire
Poor grounding in the power steering circuit prevents proper voltage regulation and can cause the PCM to detect artificially elevated signals.
How to Diagnose It
- 1
Check Defective power steering pressure switch — The pressure switch may be failing or stuck in a high-voltage state, causing it to report incorrect pressure readings to the PCM.
- 2
Check Faulty power steering position switch — The position switch detects steering wheel movement and can malfunction, sending erratic high-voltage signals to the control module.
- 3
Check Corroded or damaged wiring and connectors — Oxidation or physical damage to power steering circuit wiring or connectors can cause resistance issues that result in abnormally high voltage readings.
- 4
Check Loose ground strap or broken ground wire — Poor grounding in the power steering circuit prevents proper voltage regulation and can cause the PCM to detect artificially elevated signals.
How to Fix It
- 1
Test and replace power steering pressure switch
Use a multimeter to test the pressure switch output voltage; if readings are consistently high, replace the switch with an OEM or equivalent unit.
- 2
Inspect and repair wiring and connectors
Check all power steering control circuit wiring for corrosion, fraying, or damage. Clean corroded connectors with electrical contact cleaner and reseat connections firmly.
- 3
Verify ground connections and repair as needed
Locate and inspect the PCM ground strap and all circuit ground wires for looseness or damage. Tighten or replace any defective ground connections.
- 4
Test and replace power steering control module if needed
After ruling out switches and wiring faults, test the power steering control module output; if faulty, replace with a programmed module matching your vehicle's specifications.
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