U0100: Lost Communication With ECM/PCM A
Short answer: U0100 means “Lost Communication With ECM/PCM A”. It is a standard OBD-II code, so the basic meaning is the same on every car. Below is what it means on each of the 6 cars we cover, with a link to the full page for each car.
Standard OBD-II code Same meaning on all cars (SAE J2012).
U0100 on each car
| Car | Meaning on this car | Confidence |
|---|---|---|
| Toyota Passo (1st gen) | Abnormal communication receiving with EFI (U0100/82) | high |
| Toyota Corolla (11th gen, E170) | Lost Communication With ECM/PCM A | medium |
| Toyota Corolla (10th gen, E140) | Lost Communication With ECM/PCM A | medium |
| Honda City (5th gen, GM2) | Lost Communication With ECM/PCM A | medium |
| Honda Civic (10th gen, FC) | Lost Communication With ECM/PCM A | medium |
| Suzuki Wagon R (Pakistan, K10B) | Lost Communication With ECM/PCM A | medium |
Symptoms
- Check engine light on
- Vehicle stalls and will not crank or restart
- Vehicle may start after sitting idle for a period of time, however, it would be risky to operate because it could fail again at a most inopportune…
Likely causes
- This is not a common problem. It's been my experience that the most likely failure is the ECM, PCM or transmission control module. There are at…
- A communications failure between anything in the network will cause this code. If additional codes are present to isolate the problem, diagnosis…
- The installation of performance enhancing computer chips or devices may not be compatible with the ECM or CAN bus wiring causing the lost…
- A bent or pushed out pin terminal in one of the connectors or a loose ground to the computer will cause such a code. Jumping a dead battery and…
What to check, in order
- Check battery voltage and the main fuses
- Check the connectors of the module named in the code
- Read codes from all modules with a capable scanner
Causes and checks above are the general meaning. The exact test steps and values differ by car: open your car’s page.