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 » U0104

Code U0104

Symptoms

• Check Engine Light is on

• Transmission may not shift properly

• Vehicle may go into limp mode

Common Causes

• Faulty Transmission Control Module (TCM)

• Open or shorted TCM harness

• Poor electrical connection to the TCM

Glossary

PCM: Powertrain Control Module

TCM: Transmission Control Module

Related Codes

• U0100

• U0101

Laymans terms

Your car's computer is having trouble talking to the transmission. It's like when your phone can't connect to the internet.

Explanation

The vehicle's communication network has lost communication with the transmission control module.

Technical description

U0104 is a diagnostic trouble code (DTC) that indicates a loss of communication with the Transmission Control Module (TCM). This code is set when the Powertrain Control Module (PCM) or other control modules on the vehicle's network cannot communicate with the TCM.

Diagnosis steps

• Check for other codes and diagnose them first

• Inspect TCM wiring and connectors for damage

• Test the TCM for proper operation

Repair procedures

• Repair or replace damaged wiring or connectors

• Replace the Transmission Control Module if faulty

• Perform a software update if available

Tools required

• OBD-II scanner

• Multimeter

• Wire repair tools

Estimated repair cost

$150 - $1000

Difficulty level

Moderate

Commonly affected vehicles

• Ford F-150

• Chevrolet Silverado

• Toyota Camry

Preventive measures

• Regularly inspect and maintain vehicle wiring

• Keep software updated

• Avoid harsh driving conditions

Error code type

Communication Error

User experience recommendations

• Have a professional diagnose the issue

• Avoid driving the vehicle if it goes into limp mode

• Regularly check for software updates

Warranty information

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

Historical data

U0104 has been a common issue in vehicles with complex electronic systems, particularly in models from the mid-2000s onward.

Urgency level

Moderate – While the vehicle may still operate, improper transmission function can lead to further damage.

Legal and safety notice

Operating a vehicle with transmission issues can be unsafe and may lead to further damage. Always consult a professional mechanic.

Testing conditions

• Vehicle must be in a safe, static location

• Engine off, ignition on

Component location

The Transmission Control Module is usually located near the transmission or under the hood in the engine compartment.

FAQs

Q: Can I drive my car with a U0104 code?
A: It's not recommended as it may cause further damage or unsafe driving conditions.

Q: How do I reset the U0104 code?
A: You can clear the code with an OBD-II scanner, but it will return if the underlying issue is not fixed.

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

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