U0100
High SeverityLost Communication with ECM/PCM
Network/Communication System
What Does U0100 Mean?
A module has lost CAN bus communication with the engine control module.
Common Fix
Repair CAN bus wiring or replace ECM
Estimated Cost (DIY)
$0 - $800
Symptoms
- ⚠️Multiple warning lights
- ⚠️No start
- ⚠️Various systems not working
- ⚠️Scan tool cannot connect to ECM
Common Causes
CAN bus wiring issuelikely
Faulty ECMpossible
Blown ECM fusepossible
Corroded connectorpossible
How to Diagnose U0100
- 1Check ECM fuses
- 2Check CAN bus wiring
- 3Inspect ECM connectors
- 4Test CAN bus communication
Need to read or clear this code?
Shop OBD2 Scanners on Amazon →Frequently Asked Questions
- What is the CAN bus?
- CAN bus is the communication network that lets all vehicle modules (ECM, TCM, ABS, etc.) talk to each other.
- Can a loose connector cause U0100?
- Yes — a corroded or loose connector at the ECM is a common cause. Check all ECM connectors first.