Detailed guide for SPN 171 FMI 3
Back to top ↑What SPN 171 FMI 3 means
SPN 171 identifies ambient air temperature.
FMI 3 indicates voltage above the normal operating range or a signal circuit shorted toward a high source.
What you may notice
The outside-air temperature shown by the vehicle or diagnostic tool may be incorrect or implausibly high.
Some engine, idle-control or aftertreatment strategies can use ambient temperature as an input, so incorrect data may affect temperature-dependent functions.
What to check first
Inspect the ambient temperature sensor connector for corrosion, damaged terminals or poor contact.
Check the harness for a short to power or an open sensor ground.
Compare the reported ambient temperature with actual outside temperature after the vehicle has been parked long enough to stabilize.
Important
Do not replace the sensor solely because the displayed temperature is wrong. Wiring and connector faults can create the same FMI 3 condition.
Mechanic community notes for SPN 171 FMI 3
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