Cummins ISB4.5 CM2150 Fault Code: 2321 PID: 190 SPN: 190 FMI: 2 Engine Crankshaft Speed/Position – Data Erratic, Intermittent, or Incorrect.

Circuit Description
The engine control module (ECM) provides a 5 volt supply to the engine crankshaft speed/position sensor on the sensor supply circuit. The ECM also provides a ground on the sensor return circuit. The crankshaft speed/position sensor provides a signal to the ECM on the crankshaft speed/position sensor signal circuit. This sensor generates a signal to the ECM as the crankshaft speed indicator ring passes the sensor. The ECM interprets this signal into an engine speed reading and determines engine position based on the missing tooth on the speed indicator ring.

Conditions for Running the Diagnostics
This diagnostic runs continuously when the engine is running.

Conditions for Setting the Fault Codes
The ECM detects an intermittent or degraded signal from the crankshaft speed/position sensor over an extended period of engine operation.

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

Conditions for Clearing the Fault Code
The ECM will turn off the amber CHECK ENGINE light and the fault code state will become inactive immediately after the degraded signal from the crankshaft speed/position sensor is no longer present and the diagnostic runs and passes.

Shop Talk
During engine operation, the ECM monitors the primary speed sensor (crankshaft speed sensor) signal. Fault Code 689 will become active and light the yellow lamp if the signal from the primary speed sensor is not present or degraded for more than 3 continuous seconds. Meanwhile, if the primary engine speed sensor signal is not present or is degraded for a moment (less than 3 seconds), the ECM will interrupt injection events based on the primary engine speed sensor and resume injection events using the backup engine speed sensor. Engine power will be reduced while the injection events are based on the backup speed sensor. If the primary speed sensor signal returns, the ECM will automatically interrupt injection events based on the backup speed sensor and resume injection events based on the primary speed sensor. If over a period of time, the ECM detects several incidents of a loss of the primary speed sensor signal, this fault code will become active.

A vehicle operator can notice an intermittent “misfire” if the injection events are interrupted while the ECM switches from control based on the primary and secondary speed sensors. Also, a vehicle operator can notice intermittent “low power” if a “glitch” in the primary speed sensor signal causes the engine to intermittently use the backup speed sensor for injection control.

This fault code becomes active whenever the ECM detects a persistent loss of the primary engine speed sensor signal over a short period of time.

This fault becomes inactive at each key-on or if the ECM does not detect a loss of the primary engine speed sensor signal for at least 20 minutes.

-Intermittent loss of primary speed sensor signal; the most likely cause is an intermittent open or short circuit that can be experienced with speed sensor connector problems.
-Sensor air gap that is marginally too small or too large.

Actions to take if this fault is intermittent:
-Look for intermittent engine harness connections in the primary engine speed sensor circuit
-Look for loose connections at the ECM connector where the pins can not be locked into the socket
-Look for places where the engine harness has worn into a nearby component, causing an intermittent short circuit
-Look for pin wear at the speed sensor
-Inspect the target wheel for damage.