Cummins Fault Code
Free · no signupSPN 105 FMI 3
High idle; Excessive black smoke; Fan stays on 100% of the time.
System
Not specified
Symptom
High idle; Excessive black smoke; Fan stays on 100% of the time.
Diagnosis & fix steps
Intake Manifold Temp High (Voltage).
LOGIC: Signal > 4.5V (Open Circuit). When the wire breaks, the ECM thinks it is -40°F (or max cold), so it over-fuels and runs the fan.
ACTION: 1. Locate sensor on intake horn.
2. Jumper pins to check for FMI 4 transition.
3. Check for soot/oil buildup on the thermistor tip.
FIX: Replace Intake Air Temp Sensor or repair wire break at the connector.
Red Seal field insights
If the fan is screaming and won't turn off, check this code first. The ECM runs the fan as a safety measure when it loses the intake temp signal.
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