MediumMX-13

SPN 105 FMI 4 PACCAR MX-13 — Intake Manifold Temperat (2026)

SPN 105 FMI 4 on PACCAR MX-13 means engine intake manifold 1 temperature - voltage below normal, or shorted to low source. 60–80% of field cases trace to corroded or contaminated sensor connector. Shop repair with parts runs $25 - $110; 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 105 FMI 4 on PACCAR MX-13 tells the ECM that intake manifold temperature sensor is outside calibrated limits. On J1939, FMI 4 specifies the failure mode: Engine Intake Manifold 1 Temperature - Voltage Below Normal, Or Shorted To Low Source. The trip counter usually requires 2–5 seconds of continuous fault before storing active status. Intake manifold temperature works alongside boost pressure to help the ECM fine-tune fueling and EGR strategy, and SPN 105 FMI 4 means that input has dropped out with a shorted-low reading. ProfessionalDieselRepair.com typically finds this comes down to a corroded or contaminated connector at the sensor’s mounting point on the manifold itself, since it’s directly exposed to engine bay conditions including oil mist and moisture over time.

Common Symptoms

• Slightly reduced performance from conservative default fueling (100% of cases)
• Amber Check Engine lamp (80% of cases)
• Reported intake manifold temperature pegged at an unrealistic cold value (60% of cases)
• No dramatic drivability complaint in most cases (40% of cases)

Likely Causes (Ranked by Probability)

1. Corroded or contaminated sensor connector (45% of cases) — The sensor’s location directly on the intake manifold exposes its connector to oil mist, moisture, and heat cycling that accelerates corrosion.

2. Chafed wiring shorting the signal to ground (25% of cases) — Harness routing near the manifold can wear through insulation over time, creating a short-to-ground path.

3. Failed sensor element (15% of cases) — Internal sensor failure can independently produce a shorted-low reading, though it’s less common than connector or wiring issues in this location.

Step-by-Step Diagnostic Guide

1. Pull the fault with PACCAR Davie4 and confirm SPN 105 FMI 4 is active; check the reported intake manifold temperature value, which will likely be pegged at an extreme cold reading. — Tool: scan tool or multimeter. Document readings on the work order.

2. Locate the sensor, typically threaded into the intake manifold itself, and inspect the connector for corrosion or a pinched wire nearby. — Tool: scan tool or multimeter. Document readings on the work order.

3. Disconnect the sensor and check the signal wire for continuity to ground with the harness isolated from the ECM - any unexpected continuity confirms a short. — Tool: scan tool or multimeter. Document readings on the work order.

4. Test the sensor’s resistance at a known temperature and compare against the manufacturer’s resistance-versus-temperature chart to rule the sensor element in or out. — Tool: scan tool or multimeter. Document readings on the work order.

5. Repair any chafed wiring found, or replace the sensor if it fails the resistance test. — Tool: scan tool or multimeter. Document readings on the work order.

6. Clear the code and confirm the reported temperature climbs realistically as the engine warms up during a test run before returning the truck to service. — Tool: scan tool or multimeter. Document readings on the work order.

Repair Options (with Costs)

Repair	DIY	Independent Shop	Dealer
Intake Manifold Temperature Sensor wiring repair	$25–$150	$150–$350	$250–$500
Intake Manifold Temperature Sensor sensor/part	$25 - $110	$$25 - $110 + labor	$180+
Full module replacement	N/A	$600–$1,500	$180+

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 105 FMI 4 sets when intake manifold temperature 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

• Intake Manifold Temperature 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

Replacing the sensor without cleaning the connector first — It’s a quick swap that seems like the obvious fix - a minor parts-cannon habit that skips an easy first step.. Instead: Clean and inspect the connector thoroughly, checking for contamination, before replacing the sensor outright.

Shop Notes from the Field

Shop tip: this sensor threads directly into the intake manifold, so check for oil or coolant contamination at the connector too, not just corrosion from moisture. ProfessionalDieselRepair.com always cleans and inspects the whole connector area thoroughly before assuming the sensor element itself has failed.

Safety Warning

• Allow the intake manifold to cool if the engine has been running before disconnecting the sensor.
• Disconnect the battery before repairing any chafed wiring near the manifold area.

Prevention Tips

• Inspect the intake manifold temperature sensor connector for contamination during routine PM services.
• Address any oil leaks near the intake manifold promptly to prevent connector fouling.
• Apply dielectric grease to the connector when reassembling after any inspection.

PACCAR Field Notes for SPN 105 FMI 4

• Compare this unit’s repair history: repeat SPN 105 FMI 4 within 5,000 miles indicates incomplete prior repair, not a new component failure.
• If intake manifold temperature 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 intake manifold temperature 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 105 FMI 4 on MX-13 — many bulletin fixes address harness routing rather than sensor replacement.
• Torque intake manifold temperature 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 intake manifold temperature sensor often clear after warm-up when moisture is the root cause.
• Compare this unit’s repair history: repeat SPN 105 FMI 4 within 5,000 miles indicates incomplete prior repair, not a new component failure.
• If intake manifold temperature 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 intake manifold temperature 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 105 FMI 4 on MX-13 — many bulletin fixes address harness routing rather than sensor replacement.
• Torque intake manifold temperature 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.

Related Codes

• SPN 105 FMI 3 — often stacks with SPN 105 FMI 4
• SPN 172 FMI 4 — often stacks with SPN 105 FMI 4
• SPN 1127 FMI 18 — often stacks with SPN 105 FMI 4

FAQ

Can I drive with SPN 105 FMI 4 active?

Yes, the truck remains drivable using a default fueling strategy, though performance may be slightly reduced. Schedule the repair at your next convenient service.

How do I reset SPN 105 FMI 4 without a scan tool?

You need Davie4 or a comparable scan tool to clear the stored code after the sensor circuit is repaired; there’s no manual reset from the dash.

Is wiring or the sensor itself more likely to be the cause?

Connector corrosion or contamination is the more common cause given this sensor’s exposed location directly on the intake manifold - check that before replacing the sensor.

What does SPN 105 FMI 4 mean on PACCAR MX-13?

SPN 105 FMI 4 means engine intake manifold 1 temperature - voltage below normal, or shorted to low source. The ECM detected intake manifold temperature sensor outside calibrated limits. Verify with freeze-frame data before clearing.

Can I drive with SPN 105 FMI 4 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 105 FMI 4?

DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $25 - $110. Dealer pricing runs $180+.

What is the most common cause of SPN 105 FMI 4?

Corroded or contaminated sensor connector — confirm with visual inspection and live data before ordering parts.

Sources

• SAE J1939-71 — SPN 105 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
• Intake Manifold Temperature Sensor diagnostic guide
• SPN 105 FMI 3
• SPN 172 FMI 4