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 » U0649

Code U0649

Symptoms

• Air conditioning not working

• Check engine light on

• Unusual climate control behavior

Common Causes

• Faulty A/C Control Module

• Damaged wiring or connectors

• Network communication issues

Glossary

OBD-II: On-Board Diagnostics, a standardized system for vehicle diagnostics.

A/C Control Module: The electronic unit that controls the air conditioning system.

Related Codes

• U0100

• U0140

Laymans terms

This code means that one of the car's computers is having trouble talking to another computer. It's like when your phone can't connect to Wi-Fi.

Explanation

The vehicle's communication network is experiencing a problem, specifically with the data transfer between modules.

Technical description

U0649 is a diagnostic trouble code indicating a loss of communication with the A/C Control Module. This means the vehicle's main computer is not receiving signals from the A/C control unit.

Diagnosis steps

• Check for other related codes.

• Inspect wiring and connectors for damage.

• Test the A/C Control Module for proper operation.

Repair procedures

• Repair or replace damaged wiring/connectors.

• Replace the A/C Control Module if faulty.

• Clear the codes and test the system.

Tools required

• OBD-II scanner

• Multimeter

• Wiring diagram

Estimated repair cost

$100 - $500

Difficulty level

Moderate

Commonly affected vehicles

• Toyota Camry

• Honda Accord

• Ford Fusion

Preventive measures

• Regularly inspect vehicle wiring.

• Ensure all connectors are secure.

• Perform routine vehicle diagnostics.

Error code type

Communication Error

User experience recommendations

• Have the vehicle inspected by a professional.

• Avoid using the A/C until the issue is resolved.

Warranty information

Check if the vehicle's warranty covers electronic module repairs.

Historical data

This code has been reported in vehicles with complex electronic systems, especially those with integrated climate control.

Urgency level

Moderate – It may not affect drivability immediately, but should be addressed to ensure comfort and avoid further issues.

Legal and safety notice

Ignoring this code may lead to discomfort and potential damage to the vehicle's electronic systems.

Testing conditions

• Vehicle ignition on

• A/C system activated

Component location

The A/C Control Module is typically located behind the dashboard near the climate control panel.

FAQs

Q: Can I drive with a U0649 code?
A: Yes, but your air conditioning may not work properly. It's best to have it checked soon.

Q: Will this code affect other systems?
A: It primarily affects the A/C system, but prolonged issues could impact other electronic systems.

Last updated: Oct 29, 2025 • Source: internal database

Diagnose Your Check Engine Light