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SPN 3840 — Auxiliary Input/Output #17

Safe to driveDrivable, but watch it yourself

J1939 code SPN 3840. Below — how the fault is worded at the factory by Mercedes-Benz, and what the second half of the code (FMI) means in the standard.

Mercedes-Benz

FMI 3Frequency Output 4/15 Circuit shorted to Ubat
FMI 4Frequency Output 4/15 Circuit shorted to GND
FMI 5Frequency Output 4/15 Open Circuit (broken wire, terminal floating)

What FMI means in J1939

SPN 3840 FMI 33840/3 · 3840.3voltage above normal or shorted high
SPN 3840 FMI 43840/4 · 3840.4voltage below normal or shorted to ground
SPN 3840 FMI 53840/5 · 3840.5current below normal or open circuit

Can I keep driving

Safe to drive. Below — how much time you have and what happens if you keep going.

What happens if you keep driving

Time you have: Drivable, but watch it yourself

This is an electrical fault: an open, a short or a bad contact in the sensor circuit. The value it measures is most likely fine.

You can drive. But until the circuit is repaired this system runs blind and cannot warn you about a real failure.

Nearby: other

Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.