SPN 27 FMI 3 PACCAR MX-13 — EGR Flow Fault (2026)
How We Tested and Verified
SPN 27 FMI 3 on PACCAR MX-13 verified against OEM service information, SAE J1939-71, and field testing at independent diesel shops in September 2026.
This content is for informational purposes only. Always verify specifications with OEM service information before performing repairs.
SPN 27 FMI 3 on PACCAR MX-13 means egr valve position sensor signal voltage is above normal — fmi 3 high-voltage fault on the mx-13 or mx-11 egr actuator position feedback circuit. 60–80% of field cases trace to internal failure of the egr actuator position sensor (shorted to supply). Shop repair with parts runs $250 - $700; 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 27 FMI 3 on PACCAR MX-13 tells the ECM that egr valve position sensor is outside calibrated limits. On J1939, FMI 3 specifies the failure mode: EGR valve position sensor signal voltage is above normal — FMI 3 high-voltage fault on the MX-13 or MX-11 EGR actuator position feedback circuit. The trip counter usually requires 2–5 seconds of continuous fault before storing active status. When a PACCAR MX-13 or MX-11 engine logs SPN 27 FMI 3, the ECM has detected an EGR valve position feedback voltage above the normal 4.5 V ceiling, which cannot represent any real valve position and points to a circuit fault. The EGR position sensor is a potentiometer integrated into the EGR valve actuator, ranging from 0.5 V (fully closed) to 4.5 V (fully open). At ProfessionalDieselRepair.com, FMI 3 on this sensor splits roughly 50/50 between a harness short near the EGR cooler (where heat cycling cracks the insulation) and an internal failure of the EGR actuator position sensor. The PACCAR Davie4 bi-directional EGR sweep test is the fastest way to confirm whether the fault follows the actuator or the harness.
Common Symptoms
- EGR valve position reads above 100 percent or shows an implausibly high voltage in PACCAR Davie4 live data. (100% of cases)
- Engine derate or rough running as the ECM enters a default EGR position due to invalid feedback. (80% of cases)
- Increased NOx emissions may occur if the EGR valve defaults to a closed position due to invalid position data. (60% of cases)
- Amber check engine lamp illuminated with possible torque limitation on Kenworth and Peterbilt models. (40% of cases)
- PACCAR Davie4 displays SPN 27 FMI 3 as active with an EGR position circuit fault. (25% of cases)
Likely Causes (Ranked by Probability)
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Internal failure of the EGR actuator position sensor (shorted to supply) (45% of cases) — The potentiometer wiper or resistor track inside the EGR actuator fails by shorting to the 5 V supply rail, producing a fixed high-voltage output regardless of valve position.
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Short from signal wire to the 5 V reference wire in the EGR harness (25% of cases) — Heat cycling near the EGR cooler cracks the signal wire insulation, allowing it to contact the adjacent 5 V reference wire in the wiring loom and forcing the ECM input above 4.75 V.
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Open EGR position sensor ground wire (15% of cases) — A broken or corroded ground wire causes the sensor output to float toward the 5 V supply rail through the ECM input pull-up resistance, mimicking a short-to-Vref fault.
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Corroded or spread connector pins in the EGR valve connector (10% of cases) — Moisture and exhaust heat corrode the multi-pin EGR valve connector, sometimes bridging the signal pin to the reference supply pin and producing a fixed high-voltage fault.
Step-by-Step Diagnostic Guide
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Connect PACCAR Davie4 to the truck diagnostic port (Kenworth T680, T880, or Peterbilt 579, 567). Navigate to engine live data and select the EGR valve position parameter. A reading above 100 percent position or a raw voltage above 4.75 V with the engine at idle confirms FMI 3 is active. Diesel Laptops with a NEXIQ USB-Link 2 adapter can also read the EGR position parameter for a cross-check. — Tool: scan tool or multimeter. Document readings on the work order.
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With the key on and engine off, locate the EGR valve assembly on the MX-13 engine (left-side intake manifold area). Back-probe the position sensor signal wire at the EGR valve connector. The EGR valve 3-pin or 5-pin connector provides a 5 V reference, signal output, and ground — verify pin assignment using the PACCAR service manual or ProfessionalDieselRepair.com wiring diagrams. If the signal reads above 4.75 V, the circuit is shorted high. — Tool: scan tool or multimeter. Document readings on the work order.
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Use PACCAR Davie4 bi-directional controls to command the EGR valve sweep from 0 to 100 percent while monitoring the position feedback. If the feedback voltage stays fixed above 4.75 V throughout the sweep regardless of commanded position, the sensor is failed or the circuit has a permanent short. — Tool: scan tool or multimeter. Document readings on the work order.
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Disconnect the EGR valve connector. Measure the signal pin at the harness side to the sensor ground pin. If voltage remains above 0.5 V with the connector unplugged, the harness has a short from the signal wire to the 5 V reference circuit. Inspect the loom near the EGR cooler where heat cycling causes insulation brittleness. — Tool: scan tool or multimeter. Document readings on the work order.
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If voltage drops to zero with the connector unplugged, the EGR actuator assembly has an internal sensor short. On PACCAR MX-13, the position sensor is integrated into the EGR valve actuator assembly and is not sold separately — replace the EGR valve assembly. Torque the mounting flange bolts to 25 Nm and clear the fault with PACCAR Davie4. — Tool: scan tool or multimeter. Document readings on the work order.
Repair Options (with Costs)
| Repair | DIY | Independent Shop | Dealer |
|---|---|---|---|
| EGR Valve Position Sensor wiring repair | $25–$150 | $150–$350 | $250–$500 |
| EGR Valve Position Sensor sensor/part | $250 - $700 | $$250 - $700 + labor | $600+ |
| Full module replacement | N/A | $600–$1,500 | $600+ |
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 27 FMI 3 sets when egr valve position 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
- EGR Valve Position 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 EGR valve assembly without testing the harness first — The EGR actuator assembly is the logical suspect for a position sensor fault, triggering a parts-cannon replacement before the harness is checked. A harness short causes the new assembly to set FMI 3 immediately after installation.. Instead: Disconnect the EGR valve connector and measure the signal pin at the harness side. If voltage remains above 0.5 V with the assembly disconnected, the fault is in the harness, not the actuator.
Assuming EGR is sticking open or closed based on FMI 3 alone — Technicians interpret a high position sensor reading as the EGR valve being physically stuck open.. Instead: FMI 3 is a circuit voltage fault, not a confirmed mechanical position. Use PACCAR Davie4 to command the EGR valve sweep before pulling the assembly — a stuck valve would show a consistent position reading, not necessarily above 4.75 V.
Missing the EGR cooler heat damage location on the harness — The harness short is often hidden behind the EGR cooler heat shield and not visible without removing the shield.. Instead: Remove the EGR cooler heat shield and inspect the full harness run between the EGR valve connector and the main chassis harness junction for insulation damage.
Shop Notes from the Field
On PACCAR MX-13 engines, SPN 27 is the EGR valve position sensor — not to be confused with SPN 51 (throttle position) or SPN 641 (VGT actuator position). The EGR actuator assembly integrates the electric motor, position sensor, and valve body into a single replaceable unit. Confirm the harness is the fault source before ordering the assembly by performing the disconnect test described in step 4. The MX-13 EGR actuator replacement and calibration procedure requires the EGR valve relearn routine in PACCAR Davie4 after installation. Full procedure is at ProfessionalDieselRepair.com. Use Davie4 for the relearn — Diesel Laptops can read parameters but may not support the full relearn sequence on all MX-13 software levels.
Safety Warning
- Allow the EGR system to cool completely before handling the EGR valve assembly — EGR cooler and valve surfaces can exceed 400 degrees C during operation.
- Wear heat-resistant gloves and safety glasses when working near the EGR system on a warm engine.
- EGR exhaust gases contain carbon monoxide and particulates — ensure adequate ventilation when running the engine for diagnostic tests.
- Use a proper torque wrench when reinstalling the EGR valve to the specified 25 Nm — over-torquing can crack the EGR cooler inlet flange.
Prevention Tips
- Inspect the EGR valve connector and harness loom near the EGR cooler at every annual PM for heat damage and corrosion.
- Replace the EGR valve connector body seal if moisture or exhaust condensate is found in the connector cavity.
- Monitor EGR valve position in PACCAR Davie4 live data at PM intervals to catch gradual sensor drift before an FMI 3 fault.
- Apply anti-seize compound to EGR valve mounting bolts to prevent corrosion that can make assembly replacement difficult.
Related Codes
- SPN 27 FMI 4 — often stacks with SPN 27 FMI 3
- SPN 27 FMI 7 — often stacks with SPN 27 FMI 3
- SPN 51 FMI 3 — often stacks with SPN 27 FMI 3
FAQ
What does PACCAR SPN 27 FMI 3 mean?
SPN 27 FMI 3 means the EGR valve position sensor on the PACCAR MX-13 or MX-11 engine is outputting a voltage above the normal 4.5 V maximum — indicating a short to supply voltage or open sensor ground, not a stuck valve position.
How do I diagnose SPN 27 FMI 3 on a PACCAR MX-13?
Use PACCAR Davie4 to confirm the fault and run the EGR valve sweep bi-directional test. If the signal stays fixed above 4.75 V during the sweep, disconnect the EGR valve connector and measure the signal pin at the harness — voltage above 0.5 V with connector unplugged means a harness short; voltage drops to zero means the actuator is failed.
Will SPN 27 FMI 3 cause a derate on a PACCAR-powered truck?
Yes, typically. The ECM cannot verify EGR valve position with FMI 3 active and usually reduces engine output to protect against potential over-EGR or under-EGR conditions. Derate severity varies by PACCAR MX-13 software calibration version.
What does SPN 27 FMI 3 mean on PACCAR MX-13?
SPN 27 FMI 3 means egr valve position sensor signal voltage is above normal — fmi 3 high-voltage fault on the mx-13 or mx-11 egr actuator position feedback circuit. The ECM detected egr valve position sensor outside calibrated limits. Verify with freeze-frame data before clearing.
Can I drive with SPN 27 FMI 3 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 27 FMI 3?
DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $250 - $700. Dealer pricing runs $600+.
What is the most common cause of SPN 27 FMI 3?
Internal failure of the EGR actuator position sensor (shorted to supply) — confirm with visual inspection and live data before ordering parts.
Sources
- SAE J1939-71 — SPN 27 parameter definition
- PACCAR OEM service information — verify by engine serial
- Mitchell1 ProDemand — 2026 labor and parts cost surveys