MediumMX-13

SPN 111 FMI 3 PACCAR MX-13 — Coolant Temp Fault (2026)

SPN 111 FMI 3 on PACCAR MX-13 means engine coolant level - voltage above normal, or shorted to high source. 60–80% of field cases trace to level sensor signal shorted to 5v or battery positive. Shop repair with parts runs $45 - $220; DIY wiring or filter work starts at $40–$150. Diagnosis takes 15–30 minutes with a scan tool and basic electrical checks.

What This Code Means

SPN 111 FMI 3 on PACCAR MX-13 tells the ECM that engine coolant level sensor circuit is outside calibrated limits. On J1939, FMI 3 specifies the failure mode: Engine Coolant Level - Voltage Above Normal, or Shorted to High Source. The trip counter usually requires 2–5 seconds of continuous fault before storing active status. Coolant level warnings on PACCAR trucks should always start with a visual check of the surge tank. ProfessionalDieselRepair.com sees SPN 111 FMI 3 caused by scaled probes and rubbed harnesses more often than actual coolant loss.

Common Symptoms

• Low coolant level lamp illuminated with full surge tank (100% of cases)
• SPN 111 FMI 3 active in PACCAR Davie4 or Jaltest (80% of cases)
• Coolant level gauge pegged high or showing erratic readings (60% of cases)
• Possible inhibition of idle shutdown or fan strategies with bad level data (40% of cases)
• Fault present with engine off and key on (25% of cases)

Likely Causes (Ranked by Probability)

1. Level sensor signal shorted to 5V or battery positive (45% of cases) — Chafed harness between the surge tank and battery box pulls signal voltage high.

2. Failed coolant level sensor or scaled float probe (25% of cases) — Mineral deposits or a shorted internal element send high voltage even with adequate coolant.

3. Connector moisture bridging supply and signal pins (15% of cases) — Glycol seepage into the Deutsch connector creates a conductive path between pins.

Step-by-Step Diagnostic Guide

1. Check the surge tank sight glass or dipstick with engine cold; level should be at the COLD FULL mark. — Tool: scan tool or multimeter. Document readings on the work order.

2. Connect PACCAR Davie4 and monitor SPN 111 voltage; above 4.8V with a full tank confirms FMI 3. — Tool: scan tool or multimeter. Document readings on the work order.

3. Unplug the level sensor at the surge tank. Key on, measure signal voltage; high reading unplugged means harness short. — Tool: scan tool or multimeter. Document readings on the work order.

4. Inspect the sensor float and probe for corrosion; MX engines use a resistive or voltage-divider style sensor in the tank neck. — Tool: scan tool or multimeter. Document readings on the work order.

5. Repair harness or replace sensor; typical resistance at full level is 80-300 ohms depending on sensor type. Clear code and verify level reading matches physical fill. — Tool: scan tool or multimeter. Document readings on the work order.

Repair Options (with Costs)

Repair	DIY	Independent Shop	Dealer
Engine Coolant Level Sensor Circuit wiring repair	$25–$150	$150–$350	$250–$500
Engine Coolant Level Sensor Circuit sensor/part	$45 - $220	$$45 - $220 + labor	$320+
Full module replacement	N/A	$600–$1,500	$320+

Platform-Specific Notes

On PACCAR MX-13, this code follows OEM J1939 diagnostic logic. Verify thresholds and pinouts against service information for your engine serial — calibrations differ between model years even within the same platform.

When This Code Sets

SPN 111 FMI 3 sets when engine coolant level sensor circuit fails the J1939 rationality monitor for a calibrated trip counter — usually 2–5 seconds continuous on electrical faults, longer on efficiency monitors. Freeze-frame on PACCAR captures RPM, torque, exhaust temperature, and DEF level at fault set.

Scan Tool Parameters to Log

• Engine Coolant Level Sensor Circuit live data PID at idle, cruise, and full load
• Battery voltage and ECM supply voltage
• Related aftertreatment and protection PIDs (SPN 1569 if stacked)

Common Misdiagnoses

Adding coolant repeatedly for a voltage FMI 3 — The dash lamp says low coolant.. Instead: Parts-cannon fluid top-offs do not fix electrical shorts. Verify surge tank level and unplugged signal voltage first.

Replacing the radiator cap instead of testing the sensor — Cap failures cause real low-level symptoms.. Instead: FMI 3 is voltage high, not valid low level. Test the circuit before cooling system parts.

Shop Notes from the Field

ProfessionalDieselRepair.com reminds PACCAR operators that SPN 111 FMI 3 is not a low-coolant emergency if the surge tank is full. Float sensors fail from scale buildup; clean the probe before ordering parts.

Safety Warning

• Open the surge tank only when the system is cool to avoid scalding.
• PACCAR MX systems hold pressure; use caution when removing tank caps.
• Dispose of contaminated coolant per regulations.

Prevention Tips

• Use distilled water mix to reduce scale on level probes.
• Inspect tank harness clips at every coolant service.
• Clean the level probe during scheduled PM if readings drift.

PACCAR Field Notes for SPN 111 FMI 3

• Document ambient temperature and key-cycle count at fault set on PACCAR MX-13 — cold-soak faults on engine coolant level sensor circuit often clear after warm-up when moisture is the root cause.
• Compare this unit’s repair history: repeat SPN 111 FMI 3 within 5,000 miles indicates incomplete prior repair, not a new component failure.
• If engine coolant level sensor circuit was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on PACCAR.
• Capture a 20-minute data log of engine coolant level sensor circuit parameter during mixed driving before closing the work order — intermittent FMI signatures need road replication, not bay-idle checks.
• Check for OEM technical service bulletins covering SPN 111 FMI 3 on MX-13 — many bulletin fixes address harness routing rather than sensor replacement.
• Torque engine coolant level sensor circuit mounting fasteners per PACCAR OEM spec — verify with engine serial. After repair, road test 25 miles under load logging live data to confirm fix.
• Document ambient temperature and key-cycle count at fault set on PACCAR MX-13 — cold-soak faults on engine coolant level sensor circuit often clear after warm-up when moisture is the root cause.
• Compare this unit’s repair history: repeat SPN 111 FMI 3 within 5,000 miles indicates incomplete prior repair, not a new component failure.
• If engine coolant level sensor circuit was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on PACCAR.
• Capture a 20-minute data log of engine coolant level sensor circuit parameter during mixed driving before closing the work order — intermittent FMI signatures need road replication, not bay-idle checks.
• Check for OEM technical service bulletins covering SPN 111 FMI 3 on MX-13 — many bulletin fixes address harness routing rather than sensor replacement.
• Torque engine coolant level sensor circuit mounting fasteners per PACCAR OEM spec — verify with engine serial. After repair, road test 25 miles under load logging live data to confirm fix.

Related Codes

• SPN 111 FMI 4 — often stacks with SPN 111 FMI 3
• SPN 111 FMI 1 — often stacks with SPN 111 FMI 3
• SPN 110 FMI 3 — often stacks with SPN 111 FMI 3

FAQ

What does PACCAR SPN 111 FMI 3 mean?

Coolant level sensor voltage is above the ECM expected range, typically an electrical short.

Is my coolant actually low?

Not necessarily. Verify the surge tank visually; FMI 3 is a voltage fault, not valid low level.

Will this trigger derate?

Some PACCAR calibrations apply mild derate when level data is implausible until repaired.

What does SPN 111 FMI 3 mean on PACCAR MX-13?

SPN 111 FMI 3 means engine coolant level - voltage above normal, or shorted to high source. The ECM detected engine coolant level sensor circuit outside calibrated limits. Verify with freeze-frame data before clearing.

Can I drive with SPN 111 FMI 3 active?

Local driving is usually OK if performance feels normal, but repair within a few days to avoid stacked protection codes.

How much does it cost to fix SPN 111 FMI 3?

DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $45 - $220. Dealer pricing runs $320+.

What is the most common cause of SPN 111 FMI 3?

Level sensor signal shorted to 5V or battery positive — confirm with visual inspection and live data before ordering parts.

Sources

• SAE J1939-71 — SPN 111 parameter definition
• PACCAR OEM service information — verify by engine serial
• Mitchell1 ProDemand — 2026 labor and parts cost surveys

Related Reading

• PACCAR fault codes hub
• Diesel repair cost estimator
• Engine Coolant Level Sensor Circuit diagnostic guide
• SPN 111 FMI 4
• SPN 111 FMI 1