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.

🖨️

Home » OBD2 Codes » U0077

Code U0077

Symptoms

• Check Engine Light is on

• Intermittent vehicle operation

• Failure of certain electronic systems

Common Causes

• Faulty control module

• Damaged wiring or connectors

• Short circuit in the communication bus

Glossary

Control Module: A computer within the vehicle that controls various functions.

Communication Bus: A network system that allows different parts of the vehicle to communicate.

Related Codes

• U0073

• U0100

Laymans terms

Your car's computer is having trouble talking to one of its parts, like when you can't hear your friend on the phone because of a bad connection.

Explanation

This code indicates a problem with the communication between the car's control modules.

Technical description

U0077 is a communication error code that signifies the Control Module Communication Bus 'B' Off. This means that one of the communication lines used by the vehicle's control modules to exchange data is not working properly.

Diagnosis steps

• Use an OBD-II scanner to confirm the code

• Inspect wiring and connectors for damage

• Test the communication bus for continuity

Repair procedures

• Repair or replace damaged wiring

• Replace faulty control module

• Ensure all connectors are secure

Tools required

• OBD-II scanner

• Multimeter

• Wiring diagram

Estimated repair cost

$100 - $500

Difficulty level

Moderate

Commonly affected vehicles

• Ford F-150

• Chevrolet Silverado

• Toyota Camry

Preventive measures

• Regularly inspect wiring for wear

• Avoid exposure of electrical components to moisture

• Ensure all software updates are applied

Error code type

Communication Error

User experience recommendations

• Do not ignore the Check Engine Light

• Have the vehicle inspected by a professional

• Avoid DIY repairs unless you are experienced

Warranty information

Check with your vehicle manufacturer for warranty coverage on electronic components.

Historical data

U0077 has been a common code in vehicles with complex electronic systems, especially as cars have become more reliant on computer networks.

Urgency level

Moderate – While the vehicle may still operate, ignoring this issue can lead to more significant problems.

Legal and safety notice

Operating a vehicle with unresolved OBD-II codes can lead to safety issues and may violate emissions regulations.

Testing conditions

• Vehicle at operating temperature

• Engine running

Component location

The communication bus is typically located within the vehicle's wiring harness, running between control modules.

FAQs

Q: Can I drive with a U0077 code?
A: It's possible, but not recommended as it may lead to further issues.

Q: Will a U0077 code clear itself?
A: The code may clear after repairs, but often requires manual reset.

Last updated: Oct 6, 2025 • Source: internal database

Diagnose Your Check Engine Light