SPN 105 FMI 3 | Intake Manifold Temp High Voltage Diagnostics
Factory OEM pinpoint troubleshooting flowchart, sensor multimeter testing, pinout voltages, and harness wiring diagnostics for J1939 SPN 105 FMI 3.
SPN 105 FMI 3: Intake Manifold Temperature Sensor Circuit Open / Shorted High
Intake manifold air temperature sensor signal voltage exceeded 4.90V, indicating open circuit or failed thermistor.
- Oil/soot soaked intake temperature thermistor element in intake elbow
- Broken wire in overhead engine sensor harness
2-Pin Weatherpack: Pin 1 (+5V DC Reference), Pin 2 (Signal to ECM Pin 28)
View Full Step-by-Step Diagnostic Protocol →SPN 105 FMI 3 Fault Code Description & Symptoms
SPN 105 FMI 3 indicates the Intake Manifold Temperature (IMT) sensor circuit voltage is above normal or open circuit.
Master Technician 4-Step Pinpoint Multimeter Diagnostic Flowchart
Follow these diagnostic steps using a digital multimeter (DMM) before replacing components:
- Step 1: Disconnect IMT sensor connector at intake manifold.
- Step 2: Check sensor thermistor resistance: at 68°F (20°C), resistance should measure approx 2,500 ohms (NTC thermistor).
- Step 3: Key ON, measure reference voltage on Pin 1 (must read 5.0V DC). Reading 0V indicates open in ECM wiring harness.
- Step 4: Inspect wiring harness along cylinder head runner for heat degradation or severed conductor.
J1939 CAN Datalink 60-Ohm Termination Integrity Test
Always verify CAN bus electrical health across Pins C & D of the Deutsch 9-pin diagnostic connector with ignition OFF. Resistance must measure strictly 60.0 ± 2.0 ohms. A reading of 120 ohms indicates an open terminating resistor; 0 ohms indicates a dead short.
Frequently Asked Questions & OEM Service Guidelines
Verified answers according to official factory service literature and heavy-duty maintenance procedures:
Q: How do I calculate Diesel Exhaust Fluid (DEF) consumption?
Modern EPA10-EPA24 heavy diesel Selective Catalytic Reduction (SCR) systems consume DEF at a rate of 2.0% to 3.0% of total diesel fuel burned (approximately 2 to 3 gallons of DEF per 100 gallons of fuel).
Q: How do I test a J1939 CAN bus datalink circuit with a multimeter?
With vehicle batteries disconnected, measure resistance across diagnostic port pins C (CAN-Hi) and D (CAN-Low). A healthy circuit with both 120-ohm terminating resistors intact will read exactly 60 ohms (+/- 3 ohms).
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