SPN 5491 FMI 5: DEF line heater relay, current low or open circuit
DEF line heater relay circuit is open. Type another SPN and FMI to check it.
DEF line heater relay circuit is open.
- Check the relay, its fuse and wiring.
Paste the whole line if you like: "SPN 3251 FMI 0", "3251/0" or Deere's "003251.00". Plain-words guidance; the service manual wins.
What SPN 5491 FMI 5 means
DEF line heater relay circuit is open.
FMI 5: current low or open circuit
Too little current. Usually a broken wire, an unplugged connector, or an open coil. (SAE J1939-73: Current below normal or open circuit.)
How urgent it is
Fix it today. Fix it this shift or today. Left alone it tends to become a derate.
What to check first
- Check the relay, its fuse and wiring.
Plain-words guidance for a foreman, not a repair procedure. Makers add their own codes and steps; the machine's service manual wins.
Next time, Dozer catches the code when it fires.
Plug a CAN logger into the machine's J1939 port, or connect the telematics you have. When a code fires, Dozer opens a repair ticket with the meaning, how urgent it is and what to check.
- The code, the machine and its hours on one ticket
- Severity sorted: keep working, plan a stop, or stop now
- The mechanic gets the checklist before they drive out
- Repeat codes on the same machine get flagged
LIVE EX-04 · SPN 3251 FMI 0 · plan a stop today Photo is an AI-generated stand-in, not a customer site.
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Questions crews ask
What does SPN 5491 FMI 5 mean?
DEF line heater relay circuit is open. FMI 5 means: Too little current. Usually a broken wire, an unplugged connector, or an open coil.
Can I keep running with SPN 5491 FMI 5?
Fix it today. Finish what's safe to finish, then fix it this shift. Ignoring it usually turns into a derate or a bigger repair. If the machine derates or the stop lamp is on, stop.
What should I check first for SPN 5491 FMI 5?
Check the relay, its fuse and wiring.
How do I clear SPN 5491 FMI 5?
Fix the cause first. Most codes go inactive by themselves once the condition is gone and the engine has run a key cycle or two. Clearing it with a service tool without a fix only hides it until it comes back.
Which machines show SPN 5491 FMI 5?
Any diesel that speaks SAE J1939: excavators, dozers, loaders, haul trucks, generators and on-road trucks with Cat, Cummins, Deere, Komatsu, Volvo, Kubota, Perkins and other engines. The SPN means the same thing on all of them; the fix steps can differ, so check the service manual.
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