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 » C0091

Code C0091

Symptoms

• ABS warning light on

• Reduced braking performance

• Unusual noises during braking

Common Causes

• Faulty brake pressure sensor

• Damaged wiring or connectors

• Malfunctioning ABS module

Glossary

ABS: Anti-lock Braking System

OBD-II: On-Board Diagnostics, Second Generation

Related Codes

• C0090

• C0092

Laymans terms

This code means there's a problem with a part of the car that helps it stop safely, like a sensor that tells the car when to use the brakes.

Explanation

C0091 is a chassis code related to the vehicle's braking system, particularly involving a sensor issue.

Technical description

The C0091 code is triggered when the vehicle's onboard computer detects a malfunction in the brake pressure sensor circuit. This sensor is crucial for monitoring the pressure applied to the brakes and ensuring the vehicle stops effectively.

Diagnosis steps

• Scan the vehicle for additional codes

• Inspect the brake pressure sensor and its wiring

• Test the ABS module functionality

Repair procedures

• Replace the brake pressure sensor

• Repair or replace damaged wiring

• Reprogram or replace the ABS module

Tools required

• OBD-II scanner

• Multimeter

• Wrench set

Estimated repair cost

$150 - $400

Difficulty level

Moderate

Commonly affected vehicles

• Toyota Camry

• Honda Accord

• Ford Focus

Preventive measures

• Regular maintenance checks

• Timely replacement of brake components

• Avoiding harsh braking habits

Error code type

Sensor Issue

User experience recommendations

• Have your brakes inspected regularly

• Address warning lights promptly

Warranty information

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

Historical data

C0091 has been associated with brake sensor issues in various models, often due to wear and tear or environmental factors.

Urgency level

High – This issue can affect vehicle safety and braking performance, requiring immediate attention.

Legal and safety notice

Ignoring brake system warnings can lead to decreased vehicle safety and increased risk of accidents.

Testing conditions

• Vehicle stationary with engine running

• Performing a brake test in a safe environment

Component location

The brake pressure sensor is typically located near the master cylinder or within the ABS module.

FAQs

Q: Can I drive with a C0091 code?
A: It's not recommended to drive with this code, as it can affect your vehicle's braking performance.

Q: How do I reset the ABS light?
A: Fix the underlying issue first, then use an OBD-II scanner to clear the code.

Last updated: Feb 1, 2026 • Source: internal database

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