U0100 — Lost Communication with ECM/PCM
What it means: Lost Communication with ECM/PCM.
How serious / can you keep driving: Critical. Stop as soon as it's safe.
Check first: Start with the most likely cause: CAN bus failure.
Don't risk it — look up listed providers near you and give them this code when you call.
Listed providers nearest Baltimore, MD
Closest first. Tell them U0100 and what the truck is doing. RoadService.app lists these providers and does not employ them or carry out the repair.
- 0.0 mi away — based in Baltimore, MD · (443) 680-6789
- 0.0 mi away — based in Baltimore, MD · (410) 544-3888
- 24 hour Mobile Diesel Truck Engine Repair DEF Repairs On Site Services Road Service Laptop Diagnostic Tractors & Dump Truck☎ Call0.0 mi away — based in Baltimore, MD · (443) 591-3631
Seen on: All trucks
What U0100 means
Lost Communication with ECM/PCM. Common causes: CAN bus failure, ECM power loss, wiring issue.
How serious is it?
Critical. Stop as soon as it's safe.
Most likely causes
- CAN bus failure
- ECM power loss
- wiring issue
- Ground fault
- blown fuse
- corroded connector J1939
FAQ
Lost Communication with ECM/PCM. Common causes: CAN bus failure, ECM power loss, wiring issue.
Critical — Stop as soon as it's safe.
The most common cause is: CAN bus failure. Other possibilities include ECM power loss; wiring issue; Ground fault; blown fuse; corroded connector J1939.
Stop as soon as it's safe. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Related codes
Codes that commonly appear alongside U0100, or share the same subsystem.
- ECU Power Supply — Intermittent / Erratic (SPN 627 FMI 2)
- Battery / Charging Voltage — Low (SPN 168 FMI 18)
- Engine Controller (ECM) — Internal Fault (SPN 629 FMI 12)
- Battery voltage low during crank (SPN 168 FMI 17)
- J1939 proprietary datalink lost (SPN 625 FMI 9)
- J1939 Data Link — Communication Error (SPN 639 FMI 2)
- High Speed CAN Bus Fault (U0001)
- Lost Communication with Fuel Injector Control Module (U0105)
Same symptom: Lost communication
Other datalink faults. A U-code is a network problem and is diagnosed at the datalink, not at the module that went quiet.
- Lost Communication with TCM (U0101) · Electrical, Charging & Network
- Lost Communication with Gear Shift Module (U0103) · Electrical, Charging & Network
- Lost comms with ABS (U0121) · Electrical, Charging & Network
- Lost Communication with Body Control Module (U0140) · Electrical, Charging & Network
- Invalid Data from ECM (U0401) · Electrical, Charging & Network
- Invalid Data from TCM (U0402) · Electrical, Charging & Network
Find a mechanic or related guides
General diagnostic guidance for diesel engines (Cummins, Detroit, PACCAR, Volvo, Mack and more). Not a substitute for a scan-tool diagnosis on your specific truck.