The SPN 636 FMI 31 fault code manual covers the Detroit crankshaft position sensor failure diagnostic, including the monitored parameters and the harness resistance checks used to confirm the fault. This DiagTechPro library page summarizes the official Detroit troubleshooting sheet so technicians can confirm the Crankshaft Position Sensor Failure condition before opening the full PDF.
Official document details
| Brand | Detroit (Detroit Diesel) |
|---|---|
| Model coverage | DD Series (EPA 2007-Current) heavy-duty diesel engines, including DD13, DD15 and DD16 |
| System / group | DD Series (EPA 2007-Current) / DTCs |
| Fault code | SPN 636 / FMI 31 – Crankshaft Position Sensor Failure |
| Emissions platform | All years |
| Pages | 2 |
| File size | 0.2 MB |
| Format | |
| Language | English |
SPN 636 FMI 31 troubleshooting contents
The Detroit fault code sheet walks through these sections and diagnostic steps in order:
- Fault code identification (SPN 636, FMI 31)
- Description: monitored parameter, enabling conditions, MIL lamp, 2-second duration
- Disconnect the crankshaft position (CKP) sensor
- Measure resistance across CKP pins 1 and 2 (774 to 946 ohms)
- Disconnect the 120-pin Motor Control Module (MCM) connector
- Repair the short between the harness connector and MCM pins 73 and 43
Because these Detroit sheets present pass and fail decision points rather than long narrative, technicians should record each measured value as they proceed and compare it against the limits shown before replacing any control module, harness or sensor.
Applicable truck models covered
This diagnostic applies to Detroit DD Series (EPA 2007-Current) engines built to the All years emissions configuration, covering the DD13, DD15 and DD16 used in Freightliner and Western Star trucks. It references the Motor Control Module (MCM) and Common Powertrain Controller (CPC) that manage the affected circuit. Always confirm engine calibration against the official specification on the Detroit Diesel manufacturer website before condemning any component.
Who needs this SPN 636 FMI 31 manual
Heavy-duty truck technicians, fleet maintenance teams and workshop owners diagnosing this Detroit fault code use this sheet to follow the manufacturer procedure instead of guessing. The source sheet is published by TruckFaultCodes.com (Copyright 2017) and lists the Detroit Customer Support Center at 800-445-1980 for unresolved cases.
The complete PDF is available in the DiagTechPro manuals library; a free account is required to download it.
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