Circuit DescriptionThe engine control module (ECM) provides 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 moves past 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 LocationThe camshaft position sensor is located in the top of the gear housing on the exhaust side. .

Conditions for Running the DiagnosticsThis diagnostic runs continuously when the engine speed is greater than 1200 RPM.

Conditions for Setting the Fault CodesThe Engine Control Module (ECM) detected an intermittent loss of the camshaft speed/position sensor signal.

Action Taken When the Fault Code is ActiveThe ECM logs the fault code immediately when the diagnostic runs and fails.For On-Board Diagnostics (OBD) engines, the ECM illuminates the the Malfunction Indicator Lamp (MIL) immediately when the diagnostic runs and fails.Exhaust Gas Recirculation (EGR) valve operation will be disabled.Engine torque will be reduced if the engine is operated for an extended period of time with this fault active.Conditions for Clearing the Fault CodeTo validate the repair, perform a key cycle, start the engine and run it at high idle for 5 minutes.

The fault code status displayed by INSITE™ electronic service tool 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.For On-Board Diagnostics (OBD) engines, the ECM will extinguish the Malfunction Indicator Lamp (MIL) after three consecutive trips where the diagnostic runs and passes.The Reset All Faults command in INSITE™ electronic service tool can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications.

Shop TalkDuring engine operation, the ECM monitors the secondary speed sensor (camshaft speed sensor) signal. Fault Code 778 will become active and light the yellow lamp if the signal from the secondary speed sensor is not present or degraded for more than 3 continuous seconds. If over a period of time the ECM detects several incidents of a loss of the secondary speed sensor signal, but the signal loss is short in duration, this fault code will become active. Since the secondary engine speed signal is not used for normal engine operation, a vehicle operator should not notice any symptoms related to this problem.

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

This fault becomes inactive if the ECM does not detect a loss of the secondary engine speed sensor signal for at least 20 minutes.

Problems that can cause this fault:

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 problemsSensor air gap that is marginally too small or too large, or target wheel exhibits excessive runout.Actions to take if this fault is intermittent:

Look for intermittent engine harness connections in the secondary engine speed sensor circuitLook for loose connections at the ECM connector where the pins can not be locked into the socketLook for places where the engine harness has worn into a nearby component, causing an intermittent short circuitLook for pin wear at the speed sensorInspect the target wheel for damage.

Possible Cause:1) Sensor failure2) ECM calibration