SPN 636 FMI 10 is the Detroit DD Series diagnostic trouble code for Crankshaft Position Sensor signal erratic, documented in this 2-page PDF from the DD Series (EPA 2007-Current) DTC library. The reference gives the fault description, enabling conditions and the full step-by-step troubleshooting flow a technician follows. It is sourced from the TruckFaultCodes.com Detroit fault code library (© 2017).
Official document details
| Brand | Detroit |
| Model coverage | DD Series (EPA 2007-Current) |
| System / Group | DTCs — SPN 636, FMI 10 |
| Fault | Crankshaft Position Sensor signal erratic |
| Year / Revision | All years |
| Pages | 2 |
What SPN 636 FMI 10 means
This diagnostic trouble code concerns the Crankshaft Position (CKP) sensor circuit on the DD Series engine: crankshaft position sensor signal erratic. The CKP sensor wires to pins 73 and 43 of the 120-pin Motor Control Module (MCM) connector, and a fault here disturbs the engine speed and timing signal.
How to diagnose SPN 636 FMI 10
The manual isolates the CKP sensor with resistance measurements:
- Disconnect the crankshaft position sensor and measure resistance across its pins (in-range reading is 774–946 Ω).
- Disconnect the 120-pin MCM connector and check for a short between the CKP harness pins.
- Measure each CKP harness wire to pin 73 and pin 43 of the MCM connector to find an open.
- For swapped-pin faults, verify CKP pin 1 to MCM pin 73 and CKP pin 2 to MCM pin 43 are wired correctly.
On the DD Series, the Crankshaft Position sensor feeds engine speed and position to the Motor Control Module, and a disturbed or mis-wired signal can cause hard starting, stalling or a no-start. The manual keeps the diagnosis on the harness and connector pins before any sensor is replaced.
Who needs this fault code
Technicians use this procedure to separate a bad crankshaft position sensor from a wiring or pin-out error. The exact resistance window keeps a good sensor from being replaced unnecessarily. For the underlying system design, cross-reference the official Detroit Diesel service portal.
The full PDF is available in the DiagTechPro manuals library, free account required to download.
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