SPN 190 - FMI 10 (Fault Code 121)

SPN190 FMI10
Engine Magnetic Crankshaft Speed/Position Lost One of Two Signals - Abnormal Rate of Change

Engine Crankshaft Speed/Position Sensor Circuit

Fault Code: 121
PID(P), SID(S): P190
SPN: 190
FMI: 10/10
Lamp: Amber

REASON: The Engine Control Module (ECM) has detected a loss of signal from the crankshaft position sensor.

EFFECT: Engine may not start or may be difficult to start.

Circuit Description:
The engine control module (ECM) provides a 5-VDC supply to the crankshaft position sensor on the sensor supply circuit. The ECM also provides a ground on the sensor return circuit. As holes drilled in the flywheel move past the position sensor, a signal is generated on the signal circuit. The ECM uses this signal to determine engine speed and position. Offset spacing of the drillings indicate to the ECM the engine position.

Component Location:
The crankshaft position sensor is located on the intake side of the engine, near the flywheel housing.

Conditions for Running the Diagnostics:
This diagnostic runs continuously when the keyswitch is in the ON position and the engine is running.

Conditions for Setting the Fault Codes:
The Engine Control Module (ECM) detected a loss of the crankshaft speed/position sensor while the engine was running.

Action Taken When the Fault Code is Active:
• The ECM illuminates the amber CHECK ENGINE lamp immediately when the diagnostic runs and fails.

Conditions for Clearing the Fault Code:
• To validate the repair, perform a key cycle, start the engine and let it idle for 1 minute.
• The fault code status displayed by the recommended Cummins® electronic service tool or equivalent will change to INACTIVE immediately after the diagnostic runs and passes.
• The ECM will turn off the amber CHECK ENGINE lamp immediately after the diagnostic runs and passes.
• It is necessary to use the "Reset All Faults" command in the recommended Cummins® electronic service tool or equivalent to clear this fault.

Shop Talk:
Possible causes of this fault code include:
• Crankshaft position sensor malfunction

Read More:
SPN 102 - FMI 4 (Fault Code 123)
SPN 102 - FMI 3 (Fault Code 122)


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