SPN 723 - FMI 2 (Fault Code 778)

SPN723 FMI2 (Engine Camshaft Speed/Position - Data Erratic, Intermittent, or Incorrect)
Fault Code 778
ISB, ISC, and ISL with CM2150 - Engine Magnetic Speed/Position Circuit

Fault Code: 778
PID(P), SID(S): S064
SPN: 723
FMI: 2/2

REASON: Engine Camshaft Speed/Position - Data Erratic, Intermittent, or Incorrect. The ECM has detected an error in the camshaft position sensor signal.

EFFECT: Engine can run rough. Possibly poor starting capability. Engine runs using primary engine
position sensor.

Circuit Description:
The electronic control module (ECM) provides a 5 volt supply to the engine camshaft speed/position sensor on the sensor supply circuit. The ECM also provides a ground on the sensor return circuit. The camshaft speed/position sensor provides a signal to the ECM on the camshaft speed/position sensor signal circuit. This sensor generates a signal to the ECM as the camshaft speed indicator lobe passes the sensor. The ECM interprets this signal into an engine speed reading and determines engine position. This sensor is used as a backup sensor if the primary engine crankshaft speed/position signal
is lost.

Component Location:
Both engine position sensors are located on the back side of the front gear housing above the fuel pump drive.

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

Conditions for Setting the Fault Codes:
The ECM detects a loss of the camshaft speed/position sensor for more than 1 second.

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 immediately after the ECM detects a valid signal from the camshaft speed/position sensor.

Shop Talk:
Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe™ Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM.

This fault is logged when the ECM does not receive a valid camshaft position signal.

Causes of this fault include:
• Open or short circuit of the 5 volt SUPPLY, SIGNAL, or RETURN wire in the engine harness
• Damaged or malfunctioning camshaft position sensor.
NOTE: On INSITE™ electronic service tool, the 'Camshaft Position Sensor' is referred to as 'Engine Speed Backup Sensor'.

Read More:
SPN 723 - FMI 7 (Fault Code 731)
SPN 1172 - FMI 4 (Fault Code 692)


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