Cummins ISB ECM 3990517 Repair

Is your ISB down with a no-start, no-communication, injector-circuit, or derate fault on part 3990517? This is the bench repair for the Cummins ISB ECM — the CM550 module used on 6-cylinder ISB engines and related QSB 3.9 / 5.9 CM550 applications. Reman equivalent is 3990517RX. It is not a later CM850, CM2150, or CM2250 box.

We repair failed injector drivers, power-supply faults, processor and memory issues, and water-damaged boards, then function-test the unit before it ships. Include the engine serial number (ESN) or VIN so the calibration matches the engine. Repairs include a 1 year warranty on workmanship.

Send your core or start the repair below — include engine model, ECM part number, and symptom notes so we match the correct 3990517 hardware.