Lost Communication With ECM/PCM A
What does U0100 mean?
The U0100 code means the vehicle's onboard diagnostic system has detected: Lost Communication With ECM/PCM A. This is a critical severity code.
Common Symptoms
- Check Engine Light illuminated
- Multiple warning lights on dashboard
- Engine may stall or not start
- Transmission may enter limp mode
- No data on scan tool from ECM
Probable Causes (Ranked by Likelihood)
- ECM power supply or ground failure Very High
- CAN bus wiring fault between ECM and other modules High
- Failed ECM Moderate
- Corroded ECM connector Moderate
Step-by-Step Diagnostic Procedure
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Check ECM power and ground circuits -- verify battery voltage at ECM connector
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Inspect ECM connector for corrosion or water damage
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Check CAN bus wiring from ECM to the gateway module
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Verify other modules can communicate -- if all are down, suspect CAN bus
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If ECM has power and ground but does not communicate, ECM replacement may be needed
Frequently Asked Questions
Can I drive with code U0100?
Do not drive. Lost communication codes indicate a module has stopped communicating on the vehicle network. The affected system is completely inoperative.
What causes U0100?
The most common cause is a failed module or a wiring issue in the CAN bus network. ECM power supply or ground failure is the most likely cause. Power supply, ground, and connector issues should be checked before replacing any module.
Is U0100 expensive to fix?
Repair costs range from $100 - $1500 (parts and labor). Wiring repairs are on the lower end, while module replacement is on the higher end. The module may also need to be programmed after replacement.