Detroit DD15 GHG14 (2014-16) Fault Code: SPN 1659 FMI 18 (MCM) Thermostat Error Detected

DESCRIPTION:
Thermostat error detected.

MONITORED PARAMETER:
Coolant inlet temperature sensor.

TYPICAL ENABLING CONDITIONS:
1. Engine speed 500- 2500.
2. Coolant temperature greater than 65°C (149°F).
3. Battery voltage 11 vDC0.8.
4. Average engine load 25 – 55%.
5. Idle time divided by total engine run time less than 0.8.
6. Barometric pressure greater than 755 mbar.
7. Ambient temperature greater than 10°C.
8. Coolant inlet temperature when ignition is turned on is less than 50°C.

MONITOR SEQUENCE:
None

EXECUTION FREQUENCY:
Once per drive cycle

TYPICAL DURATION:
30

DASH LAMPS:
MIL

VERIFICATION:
1. Allow engine to cool down such that coolant inlet temperature is less than 50°C (122°F).
2. Drive vehicle for 30 minutes, preferably with a trailer (loaded or unloaded) do not idle engine except when necessary.

NOTE: If any other cooling system codes, fix those first.

PROBABLE CAUSES:
1. Engine cooling system thermostat.
2. Inlet and/or outlet coolant temperature sensor.
3. Inlet and/or outlet coolant temperature sensor harness/connector.