Caterpillar Fault Code
Free · no signupCAT 171-3 (171-3)
A/C Inop / High Idle.
System
Ambient
Symptom
A/C Inop / High Idle.
Diagnosis & fix steps
LOGIC: Ambient Air Temp - Voltage Above Normal (Open).
ACTION: Locate sensor (usually in front of radiator). Check for a snapped wire.
Red Seal field insights
Insights: CAT ECMs use this for "Fan Logic." If the sensor is open, the fan might run at 100% all the time to be "safe."
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