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 » C1021

Code C1021

Symptoms

• ABS warning light on

• Brake system warning light on

• Reduced braking performance

Common Causes

• Faulty brake booster travel sensor

• Damaged wiring or connectors

• ECU malfunction

Glossary

Brake Booster: A component that amplifies the force applied to the brake pedal.

ECU: Electronic Control Unit, the computer that controls various vehicle functions.

Related Codes

• C1022

• C1023

Laymans terms

This code means there's a problem with the sensor that helps your car know how much you're pressing the brake pedal.

Explanation

The brake booster travel sensor measures how far the brake pedal is being pushed. If there's an electrical issue with this sensor, the car's computer can't accurately determine brake pedal position.

Technical description

C1021 indicates an electrical fault in the brake booster travel sensor circuit. This sensor provides feedback to the vehicle's electronic control unit (ECU) about the position of the brake pedal. A malfunction could mean a short, open circuit, or poor connection.

Diagnosis steps

• Check for any additional codes and clear them.

• Inspect the brake booster travel sensor and its wiring for damage.

• Test the sensor using a multimeter to ensure proper operation.

Repair procedures

• Replace the brake booster travel sensor if faulty.

• Repair or replace damaged wiring or connectors.

• Reprogram or replace the ECU if necessary.

Tools required

• OBD-II scanner

• Multimeter

• Screwdriver set

Estimated repair cost

$100 - $300

Difficulty level

Moderate

Commonly affected vehicles

• Toyota Camry

• Honda Accord

• Ford Focus

Preventive measures

• Regularly inspect brake system components.

• Ensure all electrical connections are secure.

• Schedule routine maintenance checks.

Error code type

Sensor Issue

User experience recommendations

• Do not ignore the warning lights on your dashboard.

• Have your brake system inspected by a professional if you notice any issues.

Warranty information

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

Historical data

This code has been reported in vehicles with electronic brake systems, particularly those with advanced driver assistance features.

Urgency level

High – Brake system issues can compromise vehicle safety.

Legal and safety notice

Driving with a faulty brake system can be dangerous and may violate vehicle safety regulations.

Testing conditions

• Vehicle parked on a level surface

• Ignition in the 'On' position

Component location

The brake booster travel sensor is typically located near the brake pedal assembly or integrated within the brake booster.

FAQs

Q: Can I drive with a C1021 code?
A: It's not recommended, as brake system issues can affect your ability to stop safely.

Q: How do I reset the C1021 code?
A: After repairs, use an OBD-II scanner to clear the code, but ensure the issue is fixed first.

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

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