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OBD power steering high circuit guide

P0637 Code Meaning UK

P0637 means “Power Steering Control Circuit High”. In plain English, the ECU or steering control module has detected a higher-than-expected signal in the power steering control circuit. This can be caused by a short to power, overvoltage, alternator charging fault, damaged wiring, bad steering control module, EPS motor issue, sensor fault or communication problem.

📅 Updated June 2026 🇬🇧 UK diagnostic guide 🛠 High-voltage steering advice
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✓ Power steering high circuit explained ✓ Can you drive advice ✓ UK repair cost guide ✓ MOT safety included
Quick answer Meaning Symptoms Causes Severity Can you drive? Repair costs Diagnosis Vehicles affected Common mistakes MOT impact Used car advice Related guides FAQs
Quick answer

What does P0637 mean?

P0637 means the power steering control circuit is reading high. The steering control module or ECU expected a normal signal, but the voltage or feedback is above the expected range.

This may happen if the circuit is shorted to battery voltage, the alternator is overcharging, the steering module has an internal fault, the EPS motor circuit is damaged, wiring has been repaired incorrectly, or a sensor/communication fault is causing the system to see the wrong signal.

P0637 is a safety-related code because the steering assistance may reduce, become unpredictable or fail completely. The car may still steer mechanically, but it can become very heavy and difficult to control.

Most important first check

Check charging voltage, EPS power supply, steering fuses, wiring shorts, grounds and steering module data.

Main risk

High circuit voltage can cause steering assistance faults, warning lights or reduced power steering.

Best next step

Test charging voltage and steering circuit wiring before replacing expensive steering parts.

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Fault code meaning

P0637 — Power Steering Control Circuit High

The power steering control circuit helps the vehicle control steering assistance. In electric power steering systems, the motor, module, torque sensor, steering angle sensor and electrical supply all work together.

When P0637 appears, the system is seeing a high circuit condition. This can mean voltage is too high, a signal wire is shorted to power, the steering module is seeing unexpected feedback or the EPS control circuit is not responding correctly.

P0637 is closely related to P0636 power steering control circuit low and P0635 power steering control circuit. P0637 is specifically the high-voltage or high-signal side of the steering control fault family.

Mechanic view

Why overvoltage and wiring shorts matter

If I see P0637, I check the charging system and wiring first. Electric power steering modules do not like unstable voltage or overcharging, and a short to power can trigger a high circuit code quickly.

I would also inspect any previous wiring repairs around the steering rack, column, battery, fusebox and engine bay. A damaged loom or wrong repair can send battery voltage into a signal circuit.

A proper diagnosis should prove whether the issue is power supply, short to voltage, sensor, EPS motor, steering module or CAN communication before replacing expensive steering parts.

Symptoms

Common symptoms of a P0637 code

Symptoms can range from a stored code to heavy steering, intermittent assistance or warning lights.

Power steering warning light

A steering wheel warning symbol or power steering message may appear.

Heavy steering

The steering may become heavy, especially when parking or turning at low speed.

Intermittent steering assistance

Assistance may come and go if the high circuit fault is intermittent.

Battery or charging warning

Overcharging or unstable voltage may trigger charging-related warnings.

Multiple warning lights

ABS, stability, engine, battery and steering warnings may appear together.

Steering feels notchy

Electric steering may feel uneven, stiff, delayed or over-assisted.

Reduced assistance mode

The EPS system may reduce assistance to protect the motor or module.

Fault after alternator repair

Incorrect charging voltage after alternator work can trigger steering circuit faults.

Engine management light

Some vehicles may also store the fault in the engine ECU.

Common causes

What causes P0637?

P0637 is usually caused by high voltage, short-to-power wiring faults, charging problems or steering module issues.

Short

Short to battery voltage

A damaged signal wire may touch a live feed and create a high circuit reading.

Charging

Alternator overcharging

Excessive charging voltage can affect EPS modules and trigger circuit faults.

Wiring

Damaged steering wiring

Trapped, rubbed, corroded or poorly repaired wiring can cause high voltage faults.

Fusebox

Fusebox or relay fault

Internal cross-feed or corrosion can send voltage where it should not be.

Connector

Corroded EPS connector

Moisture, loose pins or corrosion can cause incorrect EPS signals.

Module

Power steering control module fault

The EPS module may internally misread or create a high circuit signal.

Motor

Electric steering motor fault

A failing motor or internal control fault can affect circuit feedback.

Sensor

Torque or steering angle sensor issue

Incorrect steering input data can cause abnormal EPS operation.

Network

CAN communication fault

The steering module may receive incorrect or missing data from other systems.

Severity

How serious is P0637?

Low

Code stored only, steering feels normal, charging voltage is normal and no warning light is active.

Medium

Intermittent steering warning, unstable charging voltage, occasional heavy steering or related EPS faults.

High

Power steering assistance lost, steering very heavy, active steering warning, overcharging or unsafe handling.

Can you drive?

Can you drive with P0637?

You should only drive with P0637 if the steering feels normal, no steering warning is active and charging voltage is confirmed normal. In that situation, a short journey to a garage may be possible.

Do not drive normally if the steering is heavy, assistance cuts in and out, the steering warning light is on, or charging voltage is too high. Overvoltage and steering assistance faults can create unsafe handling.

✅ Safe for short garage trip: steering normal, warning off, charging voltage normal and no assistance loss.

⚠️ Diagnose soon: intermittent warning, stored P0637, recent alternator repair or occasional heavy steering.

🚫 Recovery may be needed: heavy steering, assistance loss, active warning, overcharging or unsafe manoeuvring.

Alternator Not Charging Battery Warning Light
Mechanic warning

High steering circuit voltage can damage modules

If the circuit is being fed too much voltage or the alternator is overcharging, sensitive steering electronics can be damaged.

If P0637 appears with P0636, P0635 or voltage faults, test the charging system and wiring before replacing the EPS unit.

P0636 Circuit Low P0635 Steering Circuit Fault Codes Hub
Typical UK repair costs

How much does P0637 cost to fix?

Costs vary depending on whether the fault is charging-related, wiring-related, sensor-related or a steering module/rack fault.

Diagnostic scan and EPS voltage test

Typical range: £60–£150.

Charging voltage test

Typical range: £40–£120.

Alternator or charging repair

Typical range: £150–£700+.

Fusebox or relay repair

Typical range: £80–£500+.

Power steering wiring repair

Typical range: £100–£500+.

EPS connector repair

Typical range: £80–£300+.

Steering angle or torque sensor repair

Typical range: £150–£600+.

Electric steering rack or column repair

Typical range: £400–£1,500+.

EPS module repair/replacement

Typical range: £250–£1,200+ depending on vehicle.

Repair Costs Guide UK OBD Fault Codes Hub
Diagnosis

How to diagnose P0637

A proper diagnosis should prove whether the high circuit fault is caused by overcharging, short-to-power wiring, EPS module failure, sensor feedback or communication problems.

✅ Scan all modules, including EPS, ABS and body control modules.

✅ Record related voltage, steering angle, CAN and EPS faults.

✅ Check battery voltage with engine off.

✅ Check charging voltage with engine running.

✅ Check for overcharging or unstable alternator output.

✅ Inspect EPS fuses, fusible links and relay feeds.

✅ Check power and ground at the steering module.

✅ Inspect EPS wiring for short to battery voltage.

✅ Inspect steering rack/column connectors for corrosion or damage.

✅ Check steering angle sensor and torque sensor data.

✅ Check CAN communication to the EPS module.

✅ Check if the fault appears after alternator or battery work.

✅ Confirm EPS rack, column or module failure only after voltage and wiring checks pass.

Real experience

What I would check first

On a real P0637 fault, I would first check charging voltage. If the alternator is overcharging or voltage is spiking, that must be fixed before steering parts are blamed.

Then I would inspect the steering circuit wiring for shorts to power. A high circuit code often means voltage is present where it should not be.

If charging voltage, fuses, grounds, connectors and wiring are good, then the EPS module, steering motor, rack or column unit becomes more likely.

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Vehicles commonly affected

Which vehicles commonly report P0637?

P0637 is a generic OBD-II code and can appear on vehicles with electric power steering, electronically assisted hydraulic steering or monitored steering control modules.

Ford

May appear on models with electric power steering where wiring, voltage or EPS module faults occur.

BMW

Can appear where electric steering assistance, steering control voltage or module communication faults are detected.

Volkswagen Group

Can appear on Volkswagen, Audi, Škoda and SEAT vehicles with EPS high-voltage or steering control faults.

Audi

May be logged where electric steering power supply, module communication or voltage-related faults occur.

Mercedes-Benz

Can appear on vehicles with electric steering systems, steering control modules or voltage supply issues.

Other manufacturers

P0637 can also appear on Vauxhall, Peugeot, Citroën, Nissan, Hyundai, Kia, Toyota and other OBD-II vehicles with monitored power steering systems.

Common mistakes

Mistakes to avoid with P0637

P0637 can be misdiagnosed if the steering rack is replaced before overvoltage and wiring shorts are checked.

Replacing the rack too quickly

A short to power or charging fault can mimic EPS rack failure.

Ignoring alternator overcharging

High charging voltage can trigger steering faults and damage modules.

Skipping wiring inspection

A high circuit fault often needs a careful check for short-to-power wiring.

Only scanning the engine ECU

The EPS module usually holds the most useful steering-specific data.

Ignoring previous repairs

Bad alternator, battery, fusebox or steering wiring repairs can create high circuit faults.

Clearing the code only

If the circuit is still high, the steering fault and warning will return.

MOT impact

Will P0637 fail an MOT?

P0637 can affect an MOT if it causes a steering warning light, heavy steering, reduced steering assistance, unsafe steering operation or related stability control warnings.

Power steering is safety-related. If assistance is weak, intermittent or missing, repair the fault before the MOT.

⚠️ Higher risk: active steering warning, very heavy steering, assistance loss, overvoltage or unsafe manoeuvring.

⚠️ Medium risk: intermittent steering warning, stored P0637 or voltage-related steering faults.

✅ Lower risk: fault repaired, steering assistance normal, voltage healthy and no warning lights.

Common MOT Failures Engine Light MOT Guide
Safety warning

Why high steering circuit faults matter

A high control circuit can mean voltage is going where it should not. That can affect steering assistance and damage control modules.

Treat P0637 as a safety-related fault, especially if the steering feels different from normal.

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Used car buying advice

P0637 on a car you want to buy

If a used car has P0637 stored, be careful. It may be a wiring or charging fault, but it may also point to an EPS module, steering rack or column issue.

Before buying, test steering assistance at low speed, check warning lights, scan the EPS module and check charging voltage. Be especially cautious if the alternator or battery has recently been replaced.

✅ Ask for a full diagnostic report, not just a cleared code.

✅ Check for P0636, P0635 and voltage-related faults.

✅ Test parking-speed steering both left and right.

✅ Check charging voltage before buying if possible.

✅ Be cautious if assistance cuts in and out.

✅ Budget carefully if EPS rack, column or module repair is needed.

Used Car Buying Guides Inspection Checklist
Negotiation warning

Do not ignore steering high circuit faults

A high circuit fault can be caused by overvoltage, wiring shorts or module failure. All of these need proper diagnosis before purchase.

If steering assistance is not reliable, treat the car as a serious buying risk.

Buying With Advisories Check MOT History
Frequently asked questions

FAQs about P0637

Common questions about P0637 power steering control circuit high faults, safe driving, repair costs and MOT impact.

What does code P0637 mean?

P0637 means the power steering control circuit has a high signal or high-voltage condition.

Is P0637 serious?

Yes. It can affect steering assistance and may make the vehicle difficult or unsafe to control.

Can I drive with P0637?

Only if steering feels normal and no warning is active. Heavy steering or assistance loss needs urgent diagnosis.

Does P0637 mean the steering rack is faulty?

Not always. Overcharging, wiring shorts, fuses, connectors or EPS module faults can also cause it.

Can alternator overcharging cause P0637?

Yes. High or unstable charging voltage can trigger steering control circuit faults.

Can bad wiring cause P0637?

Yes. A short to battery voltage, damaged loom or poor previous repair can trigger a high circuit code.

Will P0637 fail an MOT?

It can affect an MOT if steering assistance is faulty, steering is heavy or a steering warning is active.

Can I clear P0637 without fixing it?

You can clear it, but if the high circuit fault remains, the code and warning may return.

How much does P0637 cost to fix in the UK?

Diagnosis may cost £60–£150. Wiring or charging repairs may be cheaper, while EPS rack/module repair can cost £400–£1,500+.

What should I check first?

Check charging voltage, EPS wiring, fuses, power feeds, grounds and steering module fault codes.

About this guide

Written for practical UK fault finding

Motor Vehicle Expert explains diagnostic trouble codes in clear, mechanic-style language for UK drivers. This P0637 guide is designed to help you understand power steering control circuit high faults, likely causes, safe driving advice, repair costs, MOT risks and used-car buying concerns before replacing expensive steering parts.

Fault codes should always be treated as a diagnostic starting point. P0637 can involve alternator overcharging, short-to-power wiring, EPS fuses, connectors, steering modules, electric steering motors, torque sensors, steering angle data and CAN communication. Proper testing is better than guessing.

For the full fault-code library, always start with the indexed OBD Fault Codes Explained UK hub.