P0636: Power Steering Control Circuit Low

What does P0636 mean?

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. P0636 means the voltage in this circuit is too low – the wire is shorted to ground, supply voltage is low, or the driver sees a low state although it commanded 'on'. No manufacturer threshold is published.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Power steering warning, heavy steering
• Check engine light (depending on the maker)
• Idle drops when steering

Common causes

• High Signal or control wire shorted to ground (chafing)
• Medium Undervoltage from battery, alternator or ground
• Medium Steering module or pump module faulty internally
• Low Engine module driver faulty

Likelihood is a general estimate across vehicles; your make and model may differ.