Parts
$50–1000
U0100 — Lost Communication With ECM/PCM
STOPIs it safe to drive? A module stopped talking to the engine computer over the network. Can cause no-start or limp mode — this is a wiring/communication problem, not a part to throw at it.
What U0100 means
This is a NETWORK (U) code: the listed module lost communication with the ECM/PCM on the CAN bus. The named module usually isn't bad — the BUS or a power/ground is.
Most likely causes (in order)
- Blown fuse / lost power or ground to a module
- CAN bus wiring fault (CAN-H/CAN-L short, open, or corrosion)
- A single failed module dragging the whole bus down
- Corroded connector at a module or the gateway
Symptoms you might notice
- No-start or crank-no-start
- Multiple modules showing 'no communication'
- Several unrelated warning lights at once
What to check first
Don't replace the ECM. Check its power and grounds; measure CAN-H to CAN-L resistance (key off) — a healthy bus reads ~60Ω. If a module is shorting the bus, unplug modules one at a time until comms return.
Repair cost & difficulty
Labor
1–4 hr
Difficulty
Advanced