U0100 — Lost Communication With ECM/PCM "A"
NetworkhighOther computers can no longer hear the engine computer (ECM).
Symptoms
- Many warning lights on
- RPM and temperature needles drop to zero
- Engine may stall or not start
- Gearbox in limp mode
Common causes
- ECM fuse or relay faulty
- Bad ECM ground
- Damaged or rusty CAN wires
- Weak battery
- ECM faulty
How to fix
- Charge and test the battery first
- Check ECM fuses and relay
- Check ECM grounds
- Battery disconnected: about 60 Ω between CAN-H and CAN-L
- Check connectors for water or rust
Can I keep driving?
Not recommended — the engine can shut off.
Related diagrams
ToyotaPrius2009–2015
Instrument Cluster (Combination Meter) Wiring — Simplified
Pin numbers, wire colours and 3 simple diagrams: power, fuel gauge and data network.
All CarsGeneral GuidesAll years
CAN Bus Basics — CAN-H, CAN-L and the 60 Ω Test
How car computers talk on two wires, and how to test the CAN bus with a multimeter in 2 minutes.
These are the general meanings. Some companies use a code a little differently — confirm with a scanner and your car's service manual.