U0100: Lost communication with ECM / PCM 'A'
Stop driving. Get it towed or fixed first.
Can I drive with U0100?
No, stop driving safely as soon as possible. Other modules lost contact with engine computer; engine may stall or fail to start.
What does U0100 mean?
U0100 stands for Lost Communication With ECM/PCM 'A'.
Symptoms you may notice
- Multiple warning lights on dashboard simultaneously (ABS, CEL, Airbag)
- Speedometer or instrument cluster needles bouncing or freezing
- Transmission may shift harshly or default to safe limp gear
How much does it cost to fix?
Repair costs for code U0100 depend on the specific underlying root cause, ranging from simple DIY checks to component replacement. The table below lists the most common causes and rough price ranges in USD:
- Dead or critically discharged 12V vehicle battery
- Blown main ECM/PCM power fuse or relay
- Corroded engine-to-chassis ground strap
- Failed Engine Control Module (ECM)
What to do next
- If the engine cuts out or won't start, pull over safely and do not drive.
- Check battery terminals and main engine compartment fuses labeled ECM/PCM/IGN.
- Tow the vehicle to an qualified automotive repair shop.
Last updated: October 2026
Related codes
General guidance only, not a professional diagnosis. If the check-engine light is flashing, or the car is running rough, overheating or losing power, stop driving and get help.
About this code
Code U0100 is logged by auxiliary modules (like the transmission, ABS, or instrument cluster) when they stop receiving signals from the main Engine Control Module. A weak battery or blown engine power fuse is the culprit 80% of the time. Because sudden engine shutdown can occur, tow if the car behaves erratically.