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 » U0100

Code U0100

Symptoms

• Check Engine Light is on

• Engine may not start

• Poor engine performance

Common Causes

• Faulty ECM/PCM

• Open or shorted communication wires

• Poor electrical connection

Glossary

ECM: Engine Control Module

PCM: Powertrain Control Module

Related Codes

• U0101

• U0102

Laymans terms

Your car's computer isn't talking to the engine like it should. It's like when your phone loses connection to the internet.

Explanation

The vehicle's main computer has lost communication with the engine control module.

Technical description

U0100 is a diagnostic trouble code (DTC) indicating a lost communication with the Engine Control Module (ECM) or Powertrain Control Module (PCM) 'A'. This means that the ECM/PCM is not receiving or sending data to other control modules in the vehicle.

Diagnosis steps

• Check for other codes that may indicate a wiring problem

• Inspect the ECM/PCM connectors for damage

• Test the communication wiring for continuity

Repair procedures

• Repair or replace damaged wiring

• Replace faulty ECM/PCM

• Ensure all connections are secure

Tools required

• OBD-II scanner

• Multimeter

• Wiring diagram

Estimated repair cost

$200 - $1000

Difficulty level

Moderate

Commonly affected vehicles

• Chevrolet Silverado

• Ford F-150

• Toyota Camry

Preventive measures

• Regular maintenance checks

• Ensure battery connections are clean

• Avoid moisture exposure to electrical components

Error code type

Communication Error

User experience recommendations

• Have your vehicle inspected by a professional

• Avoid DIY fixes unless you have experience with vehicle electronics

Warranty information

Check if your vehicle's powertrain warranty covers ECM/PCM issues.

Historical data

U0100 is a common code that has been reported across various makes and models, often related to wiring issues.

Urgency level

High – This issue can prevent the vehicle from starting or running properly.

Legal and safety notice

Always ensure repairs are conducted by a certified professional to avoid safety hazards.

Testing conditions

• Vehicle in park or neutral

• Ignition in the 'ON' position

Component location

The ECM/PCM is typically located in the engine compartment, near the battery or firewall.

FAQs

Q: Can I drive with a U0100 code?
A: It's not recommended, as the vehicle may not run properly and could leave you stranded.

Q: How do I clear a U0100 code?
A: Clearing the code requires an OBD-II scanner, but the underlying issue must be fixed first.

Last updated: Oct 28, 2025 • Source: internal database

Diagnose Your Check Engine Light