International SPN 636 FMI 5: Crankshaft Position Sensor Open Circuit No-Start
SPN 636 FMI 5 (FMI 5) — Crankshaft Position Sensor - Current Below Normal or Open Circuit (FMI 5)
Quick Answer
International SPN 636 FMI 5 means the crankshaft position sensor circuit has an open circuit or current below normal. This is a CRITICAL no-start fault on Maxxforce and A26 engines - the ECM cannot authorize fuel injection without CKP signal. Test sensor winding resistance (400-1,000 ohms) and harness continuity with Jaltest or Diesel Laptops before replacing the sensor.
Critical — Stop Engine / Derate Risk
International SPN 636 FMI 5 on Maxxforce 13 or A26 engines indicates the crankshaft position (CKP) sensor circuit has an open circuit or current below normal. CRITICAL - the ECM uses the CKP sensor for engine speed, injection timing, and cranking fuel delivery authorization. An open circuit directly causes a hard no-start or engine shutdown with no restart capability. Diagnose with Jaltest or Diesel Laptops immediately.
Overview: International SPN 636 FMI 5
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.
Repair Snapshot
Time
2 - 3 Hours
Difficulty
Intermediate
Parts Cost
$40 - $150
Dealer Labor
$500+
Tools Required
- Jaltest diagnostic software
- Diesel Laptops USB-Link 2 adapter
- Multimeter (resistance and continuity)
- 19mm socket for CKP sensor
- Harness repair connectors and heat-shrink tubing
What SPN 636 FMI 5 Means
International SPN 636 FMI 5 on Maxxforce 13 or A26 engines indicates the crankshaft position (CKP) sensor circuit has an open circuit or current below normal. CRITICAL - the ECM uses the CKP sensor for engine speed, injection timing, and cranking fuel delivery authorization. An open circuit directly causes a hard no-start or engine shutdown with no restart capability. Diagnose with Jaltest or Diesel Laptops immediately.
Symptoms Drivers Notice
- Engine cranks but will not start - the ECM cannot confirm crank position or speed to authorize fuel injection.
- Engine may start and immediately stall as the CKP signal is lost within the first few crankshaft revolutions.
- Red Stop Engine lamp active when the fault sets during a running engine event.
- No engine speed reading on the tachometer even during active cranking.
- Possible simultaneous cam sensor fault (SPN 637) if the CKP failure also disrupts ECM timing synchronization.
Most Likely Root Causes
Chafed CKP sensor wiring harness under oil pan
CommonThe 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.
Failed CKP sensor (open sensor winding)
CommonThe 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.
Corroded sensor connector causing open circuit
OccasionalMoisture 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.
Common Misdiagnoses (Don't Waste Parts)
Parts-cannon CKP sensor replacement without harness inspection
Why it happens: 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.
Do this 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
Why it happens: 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.
Do this 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
Why it happens: 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.
Do this 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.
Master Tech Commentary
Mechanic's Notes
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.
Step-by-Step Diagnostic Procedure
- Step 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.
- Step 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.
- Step 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.
- Step 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.
- Step 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.
Professional service / OEM-level scan tools are recommended before clearing this fault for good.
Live Data & Freeze-Frame Tips
Connect via Jaltest or Diesel Laptops and monitor engine RPM signal (SPN 190) and SPN 636 status during cranking. A healthy CKP circuit shows RPM jumping to 150-250 RPM immediately on the starter engaging. With FMI 5 active, SPN 190 reads 0 RPM throughout cranking. Also check cam position (SPN 723/637) - if cam signal is present but CKP is absent, the fault is definitively in the CKP circuit, not a common supply issue.
Safety Warnings
- 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.
When to Limp In vs Tow
SPN 636 FMI 5 is a CRITICAL no-start condition. Tow the vehicle if it cannot start. If the fault set during operation and the engine has shut down, do not attempt repeated cranking - confirm CKP circuit integrity first to avoid fuel system air-lock from extended no-fuel cranking.
Prevention Tips for Fleets & Owner-Operators
- 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.
- Replace the sensor connector pigtail whenever the sensor is replaced on a high-mileage Maxxforce engine, as the original connector may be compromised from moisture exposure.
Related Fault Codes
SPN 636 FMI 2
Crankshaft position sensor erratic or intermittent - irregular signal rather than full open circuit. Points to a wiring intermittent rather than a complete break.
SPN 637 FMI 5
Cam position sensor open circuit - frequently co-sets with SPN 636 when the CKP loss disrupts ECM timing synchronization. Resolve SPN 636 first; SPN 637 usually clears as a consequence.
SPN 190 FMI 8
Engine speed abnormal update rate - the ECM cannot derive reliable RPM from the CKP, producing erratic speed data. Resolves when SPN 636 is repaired.
Frequently Asked Questions
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 software is needed to diagnose SPN 636 on International trucks?
Jaltest diagnostic software provides full International Maxxforce and A26 engine support including SPN 636 live RPM data and freeze-frame. Diesel Laptops USB-Link 2 provides the hardware interface. Both tools can monitor RPM during cranking to confirm whether the CKP signal is present.
Can I drive with International SPN 636 FMI 5 active?
No. FMI 5 is a no-start fault. If the engine has shut down with this code, it cannot restart until the CKP circuit is repaired. Tow the vehicle to a repair facility.
How much does it cost to fix SPN 636 FMI 5 on an International?
A Maxxforce or A26 CKP sensor costs $40-$150 in parts. A wiring harness repair under the oil pan adds $100-$300 in labor and materials. Dealership diagnosis and repair typically totals $500-$800 depending on the extent of harness damage found.