SPN 111 FMI 3 | Coolant Level Sensor High Voltage Diagnostics
Factory OEM pinpoint troubleshooting flowchart, sensor multimeter testing, pinout voltages, and harness wiring diagnostics for J1939 SPN 111 FMI 3.
SPN 111 FMI 3: Engine Coolant Level Sensor Circuit High (Open Circuit)
ECM detected an open circuit in the coolant surge tank level probe circuit.
- Corroded or broken 2-pin connector at bottom of plastic coolant reservoir
- Oxidized stainless steel coolant sensor probe tips inside the surge tank
2-Pin Metripack: Pin A (Signal), Pin B (Sensor Ground Return)
View Full Step-by-Step Diagnostic Protocol →SPN 111 FMI 3 Fault Code Description & Symptoms
SPN 111 FMI 3 indicates the Engine Coolant Level sensor signal 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: Verify physical coolant level in surge tank (do not open hot radiator cap).
- Step 2: Disconnect 2-pin or 4-pin surge tank sensor connector; inspect for green pin corrosion.
- Step 3: Bridge signal to ground with jumper wire: scan tool should toggle from FMI 3 (high) to FMI 4 (low), verifying ECM circuit integrity.
- Step 4: Replace surge tank sensor cartridge or complete surge tank if magnetic float is oil-soaked.
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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