SPN 627 FMI 2 — ECU Power Supply — Intermittent / Erratic
What it means: The engine ECU is seeing erratic or intermittent supply power.
How serious / can you keep driving: Serious. Limp to the next safe stop.
Check first: Check and clean battery terminals and main grounds — a bad ground mimics dozens of faults.
Don't risk it — look up listed providers near you and give them this SPN/FMI when you call.
Listed providers nearest Houston, TX
Closest first. Tell them SPN 627 FMI 2 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 Houston, TX · (832) 377-0578
- 0.0 mi away — based in Houston, TX · (713) 219-9090
- 0.0 mi away — based in Houston, TX · (713) 671-9751
What SPN 627 FMI 2 means
The engine ECU is seeing erratic or intermittent supply power. Voltage drops, bad grounds, or a failing relay can make the ECU reset or behave unpredictably — sometimes causing stalls or no-starts. Often paired with SPN 629 (controller internal) faults.
How serious is it?
Serious. Limp to the next safe stop.
Most likely causes
- Corroded or loose battery terminals, grounds, or ECU power connector
- Failing main power relay or blown/intermittent fuse
- Low battery voltage or a charging-system (alternator) problem
- Chafed power/ground harness causing intermittent open
First moves (roadside)
- Check and clean battery terminals and main grounds — a bad ground mimics dozens of faults.
- Measure battery and charging voltage; weak batteries/alternator cause erratic ECU power.
- Wiggle-test the ECU power/ground connector while watching for the fault to flicker.
- Inspect the main power relay and associated fuses before condemning the ECU.
Common misdiagnoses
- Replacing the ECU when the real fault was a corroded ground or loose battery terminal.
- Chasing engine codes that are really just symptoms of dirty ECU power.
- Overlooking a weak alternator that drops voltage under load.
FAQ
The engine ECU is seeing erratic or intermittent supply power. Voltage drops, bad grounds, or a failing relay can make the ECU reset or behave unpredictably — sometimes causing stalls or no-starts. Often paired with SPN 629 (controller internal) faults.
Serious — Limp to the next safe stop.
The most common cause is: Corroded or loose battery terminals, grounds, or ECU power connector. Other possibilities include Failing main power relay or blown/intermittent fuse; Low battery voltage or a charging-system (alternator) problem; Chafed power/ground harness causing intermittent open.
Limp to the next safe stop. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Related codes
Codes that commonly appear alongside SPN 627 FMI 2, or share the same subsystem.
- 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 ECM/PCM (U0100)
- 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 heavy-duty diesel engines (Cummins, Detroit, PACCAR, Volvo, Mack). Not a substitute for a scan-tool diagnosis on your specific truck.