U0100 Code: Lost Communication With ECM/PCM A
🟠 Moderate severity · drivable
Drivable if the engine runs, but the modules aren't communicating, which can cause various electrical faults.
What U0100 means
The engine control module (ECM/PCM) has lost communication with another control module over the vehicle's data network. This is a communication fault, often intermittent.
Symptoms
- Check engine light is on
- Multiple warning lights
- Intermittent electrical faults
- Possible no-start or limp mode
Common causes
- most common: Damaged or corroded data-network wiring
- common: Loose or corroded module connector
- common: Low battery voltage
- less common: Faulty control module
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Check the battery and charging system voltage | Yes | $0–250 |
| Have the data network and module connections diagnosed | Mechanic | $100–300 |
Frequently asked questions
Can I drive with a U0100 code?
Yes if the engine runs, but expect possible electrical quirks. Get the communication network checked soon.
What is the most common cause of U0100?
Damaged or corroded wiring in the vehicle's data network, or a low battery.
How much does it cost to fix a U0100?
Diagnosis and wiring repair typically run $100–$300.
Related codes
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.