SPN 171
INFO
Ambient air temperature
The truck's control module (ECU) reports a fault on: Ambient air temperature.
SPN 171 means a truck control module (ECU) flagged a fault on ambient air temperature, part of the Ambient system on heavy-duty diesel trucks. DERATE rates it INFO: it does not limit driving; have it checked at the next service. Part usually replaced: Ambient air temperature sensor, $25–$120 (aftermarket to dealer) plus 0.3–0.8 h labor.
Ambient
Can I keep driving?
Yes. It is informational and does not limit driving; have it checked at the next service.
Part usually replaced
Ambient air temperature sensor
$25–$120 (aftermarket to dealer)
Labor: 0.3–0.8 h
USD, part only. Labor is billed at the shop's hourly rate.
Data: DERATE verified base, updated October 2026
Related codes
Read it off your own dash
Take one photo and DERATE tells you whether you can keep driving.
Ask DERATE
DERATE assists. It does not replace inspection by a qualified technician.