SPN 729 FMI 5: intake air heater relay, current low or open circuit
Intake air heater relay circuit: current below normal or open circuit. Type another SPN and FMI to check it.
Intake air heater relay circuit: current below normal or open circuit. An electrical fault (usually a broken wire, an unplugged connector or an open coil), not a reading out of range.
- Look at the plug and harness at the intake air heater relay for rubbed, pinched, wet or green pins.
- Check supply voltage and ground at the plug (or the coil resistance on a valve or heater).
- If the wiring is good, replace the part.
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 729 FMI 5 means
Intake air heater relay circuit: current below normal or open circuit. An electrical fault (usually a broken wire, an unplugged connector or an open coil), not a reading out of range.
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
Schedule it. Put it on the next service. Watch for it to come back.
What to check first
- Look at the plug and harness at the intake air heater relay for rubbed, pinched, wet or green pins.
- Check supply voltage and ground at the plug (or the coil resistance on a valve or heater).
- If the wiring is good, replace the part.
Plain-words guidance for a foreman, not a repair procedure. Makers add their own codes and steps; the machine's service manual wins.
Other FMIs for SPN 729
| Code | What failed | Urgency |
|---|---|---|
| SPN 729 FMI 6 | current high or grounded | Schedule it |
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 729 FMI 5 mean?
Intake air heater relay circuit: current below normal or open circuit. An electrical fault (usually a broken wire, an unplugged connector or an open coil), not a reading out of range. FMI 5 means: Too little current. Usually a broken wire, an unplugged connector, or an open coil.
Can I keep running with SPN 729 FMI 5?
Schedule it. It can wait for a planned stop, but don't let it ride for weeks. If the machine derates or the stop lamp is on, stop.
What should I check first for SPN 729 FMI 5?
Look at the plug and harness at the intake air heater relay for rubbed, pinched, wet or green pins. Check supply voltage and ground at the plug (or the coil resistance on a valve or heater). If the wiring is good, replace the part.
How do I clear SPN 729 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 729 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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