Powertrain, generic · Computer and auxiliary outputs

P0637 Power Steering Control Circuit High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

P0635–P0637 concern the control or signal circuit between engine module and power steering – depending on the maker the drive of an electro-hydraulic pump or the steering load signal the engine module uses to raise idle. CARB requires power steering components to be monitored only if another diagnostic uses them, so these codes are rare and maker-specific. Mercedes-Benz stores P0635 in the electric steering module itself (no assist after start, software update); no engine module table available to us uses P0635–P0637. P0637 means the voltage in this circuit is too high – a short to battery voltage, or the driver or steering module reports a high state although 'off' was commanded; an electro-hydraulic pump may then keep running. No manufacturer threshold is published.

Likely causes

Control or signal wire shorted to battery voltage
Steering module or pump module faulty internally
Overvoltage from the alternator regulator
Engine module faulty

Symptoms

  • Power steering warning
  • Heavy steering or pump running constantly
  • Check engine light possible

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–1,500
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

power steering control circuitpower steering moduleengine control module

Related codes

P0635P0636P0550P0553P0563

References: law.cornell.edu, en.wikipedia.org.