P0637: Power Steering Control Circuit High

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.

Symptoms

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

Most 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

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the fluid level if the steering is hydraulic
2. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
3. Check the connector and wiring
4. Read the steering control module's codes with a multi-system scanner
5. Leave the repair to a professional if the steering feel changes

Good to know

• Repair difficulty: medium
• It can trigger limp mode.

What each character of P0637 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 6: Control modules and outputs
• 37: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0637?

If the steering feels stiff or uneven, drive slowly and go to a repair shop or call for roadside assistance. It is a safety system.

What causes code P0637?

The most common causes are: control or signal wire shorted to battery voltage; steering module or pump module faulty internally; overvoltage from the alternator regulator.

Related codes

• P0635Power Steering Control Circuit
• P0636Power Steering Control Circuit Low
• P0550Power Steering Pressure Sensor/Switch Circuit
• P0553Power Steering Pressure Sensor/Switch Circuit High
• P0563System Voltage High

Sources

• law.cornell.edu: 13 CCR 1968.2
• en.wikipedia.org: Power steering

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.