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 » U0678

Code U0678

Symptoms

• Warning light on the dashboard

• Intermittent system failures

• Loss of certain vehicle functions

Common Causes

• Faulty control module

• Damaged wiring or connectors

• Network communication failure

Glossary

ECU: Engine Control Unit

OBD-II: On-Board Diagnostics, Second Generation

Related Codes

• U0100

• U0121

Laymans terms

Your car is having trouble talking to one of its parts. It's like when your phone can't connect to Wi-Fi.

Explanation

The vehicle's computer system is unable to communicate with a specific module.

Technical description

U0678 is a communication error code indicating that the vehicle's central computer (ECU) has lost communication with a specific control module. This could be due to a wiring issue, a faulty module, or a network problem.

Diagnosis steps

• Scan the vehicle for additional codes

• Inspect wiring and connectors for damage

• Test the suspected module for functionality

Repair procedures

• Repair or replace damaged wiring or connectors

• Replace the faulty control module

• Reprogram or update the module software

Tools required

• OBD-II scanner

• Multimeter

• Diagnostic software

Estimated repair cost

$100 - $500

Difficulty level

Moderate

Commonly affected vehicles

• Ford F-150

• Chevrolet Silverado

• Toyota Camry

Preventive measures

• Regularly check and maintain vehicle wiring

• Ensure software updates are applied

• Avoid exposure to extreme conditions

Error code type

Communication Error

User experience recommendations

• Have the vehicle inspected by a professional

• Avoid driving until the issue is resolved

• Keep a record of any recurring problems

Warranty information

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

Historical data

U0678 has been a common issue in vehicles with complex electronic systems, often related to aging wiring or software bugs.

Urgency level

Moderate – Should be addressed soon to avoid further issues.

Legal and safety notice

Ignoring this code may lead to safety issues or vehicle malfunction.

Testing conditions

• Vehicle at operating temperature

• All electrical systems active

Component location

The affected module is typically located within the vehicle's dashboard or engine bay.

FAQs

Q: Can I drive with code U0678?
A: It's best to have the issue checked as soon as possible to avoid potential safety risks.

Q: Will resetting the code fix the problem?
A: Resetting may clear the code temporarily, but the underlying issue needs to be fixed.

Last updated: Jan 15, 2026 • Source: internal database

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