CriticalMX-13

SPN 111 FMI 1 PACCAR MX-13 — Coolant Temp Fault (2026)

SPN 111 FMI 1 on PACCAR MX-13 means engine coolant level - data valid but below normal operating range - most severe level. 60–80% of field cases trace to coolant hose or clamp failure. Shop repair with parts runs $40 - $600; 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 1 on PACCAR MX-13 tells the ECM that engine coolant level sensor is outside calibrated limits. On J1939, FMI 1 specifies the failure mode: Engine Coolant Level - Data Valid But Below Normal Operating Range - Most Severe Level. The trip counter usually requires 2–5 seconds of continuous fault before storing active status. ProfessionalDieselRepair.com always pressure-tests the cooling system cold before restarting a truck that’s had this critical shutdown, since a small leak can easily be missed on a visual inspection alone.

Common Symptoms

• Red Stop Engine lamp with loud warning buzzer (100% of cases)
• Automatic engine shutdown sequence (80% of cases)
• Coolant temperature gauge climbing rapidly before shutdown (60% of cases)
• Visible coolant loss or empty reservoir tank (40% of cases)

Likely Causes (Ranked by Probability)

1. Coolant hose or clamp failure (45% of cases) — Mechanical fault - a failed hose or loose clamp allows coolant to escape, sometimes gradually enough to go unnoticed until a critical level is reached.

2. Radiator or water pump leak (25% of cases) — Mechanical fault - a developing leak from either component can slowly drain the system over time or fail suddenly.

3. Cracked coolant reservoir tank (15% of cases) — Mechanical fault - a hairline crack in the plastic tank, often at a weld seam, causes a slow leak that’s easy to miss visually.

4. Head gasket failure allowing internal coolant loss (10% of cases) — Serious mechanical failure - coolant is consumed internally rather than leaking externally, often accompanied by white exhaust smoke or oil contamination.

Step-by-Step Diagnostic Guide

1. Pull over safely and shut off the engine immediately if it hasn’t already shut down on its own. — Tool: scan tool or multimeter. Document readings on the work order.

2. Let the engine cool completely before opening any part of the cooling system, then visually inspect the reservoir tank and radiator for coolant level. — Tool: scan tool or multimeter. Document readings on the work order.

3. Check the bottom of the radiator, water pump, and all hose connections for active leaks or damp residue indicating a slow leak. — Tool: scan tool or multimeter. Document readings on the work order.

4. Pressure-test the cooling system once safely cooled to identify the leak source before refilling and restarting. — Tool: scan tool or multimeter. Document readings on the work order.

5. Do not restart the engine until the leak is found and repaired, or you risk repeating the same shutdown event or causing real overheating damage. — Tool: scan tool or multimeter. Document readings on the work order.

Repair Options (with Costs)

Repair	DIY	Independent Shop	Dealer
Engine Coolant Level Sensor wiring repair	$25–$150	$150–$350	$250–$500
Engine Coolant Level Sensor sensor/part	$40 - $600	$$40 - $600 + labor	$550+
Full module replacement	N/A	$600–$1,500	$550+

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 1 sets when engine coolant level sensor 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 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

Refilling the coolant and restarting without finding the leak source — Refilling seems like a complete fix that gets the truck moving again quickly.. Instead: This risks repeating the exact same critical shutdown - pressure-test the system cold to find the leak before restarting and returning to service.

Replacing the coolant level sensor for a confirmed physically low coolant condition — Any level-related code can be mistaken for a sensor problem.. Instead: This FMI (1, data valid) means the ECM trusts the reading as real - this is a parts-cannon mistake when the actual problem is a physical coolant leak, not the sensor.

Shop Notes from the Field

ProfessionalDieselRepair.com pressure-tests the system cold every time before assuming a false alarm - a hairline crack in the reservoir tank or a failing hose clamp can cause this exact critical shutdown without an obvious puddle underneath.

Safety Warning

• Never open a hot cooling system - allow full cooling before removing any cap or fitting.
• Watch for scalding coolant spray if pressure remains in a partially failed system.

Prevention Tips

• Inspect all coolant hoses and clamps during PM service for cracking or looseness.
• Pressure-test the cooling system annually to catch developing leaks early.
• Address any gradual coolant level drop immediately rather than repeatedly topping it off.

PACCAR Field Notes for SPN 111 FMI 1

• Check for OEM technical service bulletins covering SPN 111 FMI 1 on MX-13 — many bulletin fixes address harness routing rather than sensor replacement.
• Torque engine coolant level sensor 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 often clear after warm-up when moisture is the root cause.
• Compare this unit’s repair history: repeat SPN 111 FMI 1 within 5,000 miles indicates incomplete prior repair, not a new component failure.
• If engine coolant level sensor 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 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 1 on MX-13 — many bulletin fixes address harness routing rather than sensor replacement.
• Torque engine coolant level sensor 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 often clear after warm-up when moisture is the root cause.
• Compare this unit’s repair history: repeat SPN 111 FMI 1 within 5,000 miles indicates incomplete prior repair, not a new component failure.
• If engine coolant level sensor was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on PACCAR.

Related Codes

• SPN 111 FMI 17 — often stacks with SPN 111 FMI 1
• SPN 110 FMI 0 — often stacks with SPN 111 FMI 1

FAQ

Can I keep driving with this code active?

No - the engine will likely shut down automatically, and continuing to drive risks severe overheating damage. Stop safely immediately.

How do I reset it without a scanner?

Don’t attempt to reset this without finding and repairing the leak first - refilling and restarting without addressing the root cause risks repeating the shutdown or causing engine damage.

What triggers the derate countdown on this code?

There typically isn’t a countdown - most PACCAR MX engines shut down immediately or within seconds of confirming critically low coolant.

What does SPN 111 FMI 1 mean on PACCAR MX-13?

SPN 111 FMI 1 means engine coolant level - data valid but below normal operating range - most severe level. The ECM detected engine coolant level sensor outside calibrated limits. Verify with freeze-frame data before clearing.

Can I drive with SPN 111 FMI 1 active?

Short distances only if power is normal. Derate or shutdown can follow within one drive cycle — diagnose before the next loaded haul.

How much does it cost to fix SPN 111 FMI 1?

DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $40 - $600. Dealer pricing runs $550+.

What is the most common cause of SPN 111 FMI 1?

Coolant hose or clamp failure — 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 diagnostic guide
• SPN 111 FMI 17
• SPN 110 FMI 0