CriticalA26

SPN 636 FMI 5 International A26 — Crankshaft Position (2026)

SPN 636 FMI 5 on International A26 means crankshaft position sensor - current below normal or open circuit (fmi 5). 60–80% of field cases trace to chafed ckp sensor wiring harness under oil pan. Shop repair with parts runs $40 - $150; 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 636 FMI 5 on International A26 tells the ECM that engine position sensor is outside calibrated limits. On J1939, FMI 5 specifies the failure mode: Crankshaft Position Sensor - Current Below Normal or Open Circuit (FMI 5). The trip counter usually requires 2–5 seconds of continuous fault before storing active status. International SPN 636 FMI 5 is a CRITICAL engine management fault on Maxxforce 13 and A26 powered trucks, indicating the crankshaft position sensor circuit has an open circuit or insufficient current. The ECM requires CKP sensor data to determine engine speed, crank position, and injection timing sequence. Without it, the engine will crank but not fire, or will immediately shut down if the signal is lost during operation. ProfessionalDieselRepair.com sees this fault frequently on high-mileage Maxxforce platforms where the sensor harness has abraded against the engine block under the oil pan. Harness inspection before sensor replacement prevents the classic parts-cannon mistake of replacing a functional sensor on a damaged wire.

Common Symptoms

• Engine cranks but will not start - the ECM cannot confirm crank position or speed to authorize fuel injection. (100% of cases)
• Engine may start and immediately stall as the CKP signal is lost within the first few crankshaft revolutions. (80% of cases)
• Red Stop Engine lamp active when the fault sets during a running engine event. (60% of cases)
• No engine speed reading on the tachometer even during active cranking. (40% of cases)
• Possible simultaneous cam sensor fault (SPN 637) if the CKP failure also disrupts ECM timing synchronization. (25% of cases)

Likely Causes (Ranked by Probability)

1. Chafed CKP sensor wiring harness under oil pan (45% of cases) — The sensor harness routing under the Maxxforce oil pan contacts the block over time. Repeated vibration wears through the insulation and eventually severs the conductor, creating an open circuit that prevents the ECM from receiving any speed signal.

2. Failed CKP sensor (open sensor winding) (25% of cases) — The magnetic pickup coil inside the sensor fails open from vibration fatigue or contamination. Infinite resistance at the sensor terminals confirms the open winding. Replacement is straightforward and low cost.

3. Corroded sensor connector causing open circuit (15% of cases) — Moisture ingress into the sensor connector oxidizes the terminals, creating a high-resistance open circuit. Cleaning and re-seating the terminals or fitting a new connector pigtail resolves the fault without sensor replacement.

Step-by-Step Diagnostic Guide

1. Connect Jaltest or Diesel Laptops diagnostic interface to the J1939 data link. Navigate to Engine > Speed Sensors and read SPN 636 FMI 5. Use the software to observe engine RPM signal during cranking - zero RPM with active cranking confirms CKP signal loss. — Tool: scan tool or multimeter. Document readings on the work order.

2. Locate the crankshaft position sensor on the International Maxxforce 13 or A26 engine (typically on the front of the engine block near the crankshaft reluctor wheel, accessible from below with the engine running protection). Inspect the connector for corrosion, bent pins, or chafed wiring near the block. — Tool: scan tool or multimeter. Document readings on the work order.

3. Unplug the CKP sensor connector and measure resistance between the two signal pins (or signal and shield on a 3-pin sensor). A healthy Maxxforce CKP sensor reads approximately 400-1,000 ohms at room temperature (NTC magnetic pickup). Infinite resistance confirms an open sensor winding. — Tool: scan tool or multimeter. Document readings on the work order.

4. If sensor resistance is normal, measure continuity on both signal wires from the sensor connector back to the ECM. FMI 5 requires an open in the circuit. Check harness routing under the oil pan where the wires commonly contact the block and abrade through the insulation over time. — Tool: scan tool or multimeter. Document readings on the work order.

5. Replace the sensor if internal resistance is infinite (torque to 18-20 ft-lb), or repair the wiring open. Clear faults with Jaltest or Diesel Laptops, crank the engine, and confirm live RPM appears in the diagnostic software immediately on engine start. — Tool: scan tool or multimeter. Document readings on the work order.

Repair Options (with Costs)

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

Platform-Specific Notes

On International A26, 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 636 FMI 5 sets when engine 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 International captures RPM, torque, exhaust temperature, and DEF level at fault set.

Scan Tool Parameters to Log

• Engine 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

Parts-cannon CKP sensor replacement without harness inspection — A no-start with an open CKP sensor code makes technicians immediately reach for a sensor. On Maxxforce platforms the harness chafe is the more common cause, and the fault returns on the new sensor within days.. Instead: Visually inspect the harness under the oil pan before ordering any sensor. Measure sensor winding resistance first - if in spec (400-1,000 ohms), the harness is the open circuit.

Diagnosing a fuel system no-start before checking CKP sensor — A cranking no-start prompts technicians to check fuel supply, fuel pressure, and injectors before electrical sensors. SPN 636 FMI 5 directly causes a no-start without any fuel system involvement.. Instead: Pull fault codes with Jaltest or Diesel Laptops first. SPN 636 FMI 5 active during a no-start points directly at the CKP circuit and eliminates the fuel system as the primary investigation area.

Replacing the cam sensor (SPN 637) for a concurrent timing fault — When the CKP signal is lost, the ECM may also set a cam sensor sync fault, misleading technicians into replacing the cam sensor instead of the CKP sensor.. Instead: Identify which sensor is the primary fault (usually SPN 636 if the CKP sets first) and resolve it. The secondary cam sync fault typically clears once the CKP circuit is restored.

Shop Notes from the Field

Shop tip from ProfessionalDieselRepair.com: International A26 and Maxxforce CKP sensor failures are often preceded by intermittent stalling events that drivers report as transmission-related or fuel-related. Always check SPN 636 history in Jaltest or Diesel Laptops before chasing fuel or transmission faults on an intermittent stall complaint. On Maxxforce 13 engines, the sensor harness routes under the oil pan and contacts the block over time; a visual inspection in this area finds the chafe point 70% of the time. Sensor replacement without harness inspection is a parts-cannon mistake on this platform - a $50 sensor on a chafed harness will set FMI 5 again within days. Always confirm with Jaltest or Diesel Laptops live RPM data during cranking before returning the truck.

Safety Warning

• Disable the ignition and remove the key before working on the CKP sensor connector or harness to prevent accidental starting.
• The CKP sensor is located near rotating components - ensure the engine is completely secured before reaching under the vehicle.
• Wear safety glasses when inspecting under the oil pan - dirt and oil often falls from the undercarriage.
• Apply thread sealant or anti-seize to the sensor threads per OEM specification and torque to 18-20 ft-lb.
• Use only OEM-quality sensors on Maxxforce and A26 engines; incorrect air gap specifications on aftermarket sensors can cause intermittent signal loss.

Prevention Tips

• Inspect CKP sensor harness routing and condition under the oil pan at every 100,000-mile major service.
• Use OEM International sensors with the correct magnetic pickup winding characteristics to prevent false opens from impedance mismatch.
• Protect any repaired harness sections with split loom and tie the harness away from the engine block contact surface.
• Check for DTCs with Jaltest or Diesel Laptops at each PM service to catch intermittent CKP signal faults before they cause a hard no-start.

Related Codes

• SPN 636 FMI 2 — often stacks with SPN 636 FMI 5
• SPN 637 FMI 5 — often stacks with SPN 636 FMI 5
• SPN 190 FMI 8 — often stacks with SPN 636 FMI 5

FAQ

What does International SPN 636 FMI 5 mean?

It means the crankshaft position sensor circuit has an open circuit or current below normal. The ECM cannot read engine speed or crank position, which prevents fuel injection authorization and directly causes a hard no-start condition.

Will SPN 636 FMI 5 prevent an International truck from starting?

Yes. Without a valid CKP sensor signal, the ECM will not authorize fuel injection on Maxxforce or A26 engines. The engine will crank without starting. If the signal is lost while running, the engine shuts down immediately.

How do I test the CKP sensor on an International Maxxforce?

Unplug the sensor and measure resistance between the two signal pins. A healthy Maxxforce CKP sensor reads 400-1,000 ohms at room temperature. Infinite resistance confirms an open sensor winding. If resistance is in spec, trace the harness for a broken wire under the oil pan.

What does SPN 636 FMI 5 mean on International A26?

SPN 636 FMI 5 means crankshaft position sensor - current below normal or open circuit (fmi 5). The ECM detected engine position sensor outside calibrated limits. Verify with freeze-frame data before clearing.

Can I drive with SPN 636 FMI 5 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 636 FMI 5?

DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $40 - $150. Dealer pricing runs $500+.

What is the most common cause of SPN 636 FMI 5?

Chafed CKP sensor wiring harness under oil pan — confirm with visual inspection and live data before ordering parts.

Sources

• SAE J1939-71 — SPN 636 parameter definition
• International OEM service information — verify by engine serial
• Mitchell1 ProDemand — 2026 labor and parts cost surveys

Related Reading

• International fault codes hub
• Diesel repair cost estimator
• Engine Position Sensor diagnostic guide
• SPN 636 FMI 2
• SPN 637 FMI 5