U1108 — No communication with the engine management ECU fault: No signal

Diagnostic algorithm

1. Confirm and record U1108 and any related DTCs from all modules; capture freeze-frame and network errors.
2. Verify vehicle battery condition and charging system; ensure stable supply voltage during diagnostics.
3. Check fuses and power feeds to the engine ECU; restore any missing power or replace blown fuses.
4. Visually inspect and secure the engine ECU connector; look for corrosion, bent pins or water damage. Repair or reseal as required.
5. Attempt to communicate with the engine ECU directly at the connector using an OEM-capable scan tool; note whether the ECU responds.
6. Measure pin voltages at the ECU harness: supply and ground pins, CAN_H and CAN_L idle voltages; compare to expected values.
7. Check CAN bus termination resistance across CAN_H and CAN_L; if out of range, isolate sections of the bus to find the fault.
8. If CAN voltages are incorrect, inspect wiring for shorts to ground/voltage and continuity between modules and junctions; repair any damaged wiring/splices.
9. Disconnect suspect modules (other than ECU) one at a time to determine if another device is causing bus domination or errors.
10. If wiring and power/ground are good and ECU does not respond, consider ECU reprogramming/reflash per manufacturer procedure; if still no communication, replace the ECU following OEM pairing/coding steps.
11. Clear DTCs and perform road/test or network verification to confirm restoration of communication.
12. Note: follow manufacturer-specific service information and safety procedures for ECU replacement and programming.