SPN 107 FMI 3 | Air Filter Restriction Sensor Diagnostics
Factory OEM pinpoint troubleshooting flowchart, sensor multimeter testing, pinout voltages, and harness wiring diagnostics for J1939 SPN 107 FMI 3.
SPN 107 FMI 3: Engine Air Filter Differential Pressure Circuit Voltage High
Air filter restriction sensor signal voltage exceeded 4.85 Volts DC, indicating an open circuit in the sensor return line.
- Disconnected harness connector at the air intake duct restriction switch
- Broken sensor ground wire in engine front harness
2-Pin Connector: Pin 1 (+5V / Signal), Pin 2 (Chassis Ground Return)
View Full Step-by-Step Diagnostic Protocol →SPN 107 FMI 3 Fault Code Description & Symptoms
SPN 107 FMI 3 indicates the Engine Air Filter Restriction differential pressure sensor circuit voltage is above normal.
Master Technician 4-Step Pinpoint Multimeter Diagnostic Flowchart
Follow these diagnostic steps using a digital multimeter (DMM) before replacing components:
- Step 1: Inspect air cleaner housing and intake piping for collapsed ductwork or physical restriction.
- Step 2: Check sensor harness connector for corrosion, water intrusion, or backed-out terminals.
- Step 3: Verify 5.0V reference across harness terminals with ignition ON.
- Step 4: Replace restriction sensor if voltage remains >4.8V with clean air filter installed.
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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