Powertrain, generic · Computer and auxiliary outputs

P0635 Power Steering Control Circuit

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. P0635 is the general or open-circuit code; output components must be checked for circuit faults, but separate low/high codes (P0636/P0637) are not mandatory. Steering assist may fail or be reduced; without the load signal idle can sag at full lock. The power steering pressure switch family is P0550–P0554.

Likely causes

Wire or connector between engine module and steering module or pump open or corroded
Software or calibration fault in the steering module (Mercedes)
Steering module or electro-hydraulic pump faulty
Undervoltage from weak battery, alternator or poor ground
Engine module faulty

Symptoms

  • Power steering warning, heavy steering
  • Check engine light (depending on the maker)
  • Idle drops when steering
  • Fault possibly only after engine start

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

P0636P0637P0550P0551P0505P0562

References: law.cornell.edu, static.nhtsa.gov, static.nhtsa.gov, en.wikipedia.org.