What is an OBD2 code?

An OBD2 (On-Board Diagnostics) code is a diagnostic trouble code (DTC) generated by your vehicle's computer system when it detects a problem. These codes help identify specific issues with your vehicle's engine, transmission, emissions, or other systems.

How do I read OBD2 codes?

To read OBD2 codes, you'll need an OBD2 scanner. Plug it into your vehicle's OBD2 port (usually located under the dashboard), turn your key to the 'ON' position, and follow your scanner's instructions to retrieve the codes. Each code starts with a letter (P, B, C, or U) followed by four numbers.

What do the different types of OBD2 codes mean?

OBD2 codes are categorized by their first letter: P (Powertrain) for engine and transmission issues, B (Body) for interior systems like airbags, C (Chassis) for mechanical systems like brakes, and U (Network) for computer and module communication problems.

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Home » OBD2 Codes » C0591

Code C0591

Symptoms

• Reduced braking performance

• Brake warning light on the dashboard

• Unusual noises when braking

Common Causes

• Faulty brake booster motor

• Damaged or corroded wiring/connectors

• Faulty control module

Glossary

Brake Booster: A device that increases the force applied to the brakes.

Current: The flow of electrical charge in a circuit.

Related Codes

• C0592

• C0593

Laymans terms

This code means there's a problem with the electric motor that helps you brake. It's not getting enough power to work properly.

Explanation

The code indicates that the current in the brake booster motor's U-V-W phases is lower than expected, which can affect the brake system's performance.

Technical description

The brake booster motor assists in applying the brakes by providing additional force. The motor operates using three-phase electrical power (U, V, and W phases). A low current condition in these phases suggests an electrical issue, possibly due to a faulty motor or wiring problem.

Diagnosis steps

• Inspect the brake booster motor and its wiring for damage.

• Check the electrical connections for corrosion or looseness.

• Test the motor's current draw using a multimeter.

Repair procedures

• Replace the brake booster motor if faulty.

• Repair or replace damaged wiring or connectors.

• Replace the control module if necessary.

Tools required

• Multimeter

• Wrench set

• Screwdriver set

Estimated repair cost

$200 - $600

Difficulty level

Moderate

Commonly affected vehicles

• Chevrolet Malibu

• Buick LaCrosse

• Cadillac CTS

Preventive measures

• Regularly inspect brake system components.

• Ensure electrical connections are secure and corrosion-free.

• Follow the manufacturer's maintenance schedule.

Error code type

Brake System Issue

User experience recommendations

• Do not ignore the brake warning light.

• Have your vehicle inspected by a professional if you notice braking issues.

Warranty information

Check with your vehicle manufacturer for warranty coverage on brake system components.

Historical data

This code commonly appears in vehicles with electric brake booster systems, particularly in models with high mileage.

Urgency level

High – Braking issues should be addressed immediately to ensure vehicle safety.

Legal and safety notice

Driving with impaired brakes can lead to accidents and is illegal in many jurisdictions.

Testing conditions

• Vehicle stationary

• Engine running

Component location

The brake booster motor is typically located near the brake master cylinder in the engine bay.

FAQs

Q: Can I drive with code C0591?
A: It's not recommended to drive with this code as it indicates potential brake issues.

Q: How do I reset the brake warning light?
A: The warning light will reset after the issue is fixed. A diagnostic tool can also be used to clear the code.

Last updated: Jun 8, 2026 • Source: internal database

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