U0100: lost communication with the ECM/PCM
U0100 is stored by other modules (gearbox, ABS, cluster) when they stop receiving messages from the engine control module. The ECU itself may be dead — or it may be a power, earth or wiring problem.
Common causes
- No power or earth to the ECU (blown fuse, failed main relay, corroded earth).
- Damaged or wet CAN-bus wiring or connectors.
- A failed ECU (power supply or processor fault).
- Another module pulling the CAN bus down.
Quick checks
- Can your diagnostic tool talk to the ECU at all?
- Check ECU fuses, relay and earths with a meter, under load.
- Look for water in the ECU connector and along the loom.
- Measure the CAN-bus resistance with the battery disconnected (about 60 ohms across CAN-H and CAN-L on most cars).
If the ECU is at fault
- We can bench-test the ECU and repair board-level faults where possible.
- If it can't be repaired, we transfer your ECU's data into a matching donor so it works with your car.
Questions
Is U0100 always the ECU?
No. Power, earth and wiring faults are common causes. Check those before replacing anything.
Need it checked?
Send your part number and a label photo — we'll tell you whether it's a repair or a clone, and the price, before you post.
Related services
Bosch Honda ECU Bench EDC17CP06 EDC17CP16 EDC17CP50
from £52.95Bosch VAG 2.0 TDI ECU EDC17C46 EDC17CP44
from £52.95Bosch VW Audi Seat Skoda 2.0 TSI ECU MG1CS008 MG1CS011
from £52.95Honda MED17.9.3 EDC17C72 Bosch Petrol Diesel ECU
from £52.95Jaguar E-Pace Land Rover Range Rover ECU MG1CS028
from £53.99Jaguar XE XF F-Type Land Rover Velar ECU MED17.9.9
from £53.99Jaguar XE XF Land Rover Evoque F-Pace ECU MED17.9.7
from £53.99Jaguar XF Land Rover Velar ECU MED17.8.3 8.31 8.32
from £53.99BMW 3-Series 5-Series X3 X5 Diesel ECU EDC17C76
from £54Engine ECU cloning · Control module & PCB repair
General guidance only — always diagnose the vehicle properly. Fault code meanings are the generic (SAE) definitions; manufacturers may add their own.