Cummins Fault Code
Free · no signup153 (SPN 105 FMI 3)
High idle; Excessive black smoke; Cooling fan locked on 100%.
System
Not specified
Symptom
High idle; Excessive black smoke; Cooling fan locked on 100%.
Diagnosis & fix steps
Intake Manifold Air Temp - Voltage High.
LOGIC: Signal > 4.5V (Open Circuit). The ECM assumes -40°F air temp and over-fuels to compensate for "cold" air density.
ACTION: 1. Locate sensor on the intake horn.
2. Jumper pins to check for FMI 4.
3. Check for soot/oil buildup on sensor tip.
FIX: Replace Intake Air Temp Sensor or repair broken wiring.
Red Seal field insights
If your fan won't stop screaming, this is your #1 suspect. The ECM defaults the fan to "On" whenever it loses the intake temperature signal.
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