Possible causes

– Faulty Camshaft Position Sensor
– Camshaft Position Sensor harness is open or shorted
– Camshaft Position Sensor circuit poor electrical connection
– Faulty starter motor
– Starting system circuit
– Dead (Weak) battery

Tech notes

On some GMC models the camshaft position sensor is part Ignition Control Module (ICM) (aka igniter)

When is the code detected?

The camshaft position sensor signal is not detected by the Engine Control Module(ECM) during the first few seconds of engine cranking

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– Lack/Loss of Power
– Engine Stall

P0340 GMC Description

The Camshaft Position Sensor is an electronic device used in an engine to record the rate at which the camshaft is spinning. This information is used by the Engine Control Module(ECM) to control ignition and fuel injection. The camshaft position sensor senses the retraction of camshaft (intake) to identify a particular cylinder. The camshaft position sensor senses the piston position. The sensor system consists of a rotating part, typically a disc, as well as a static part, the actual sensor.
When the engine is running, the high and low parts of the teeth cause the gap with the sensor to change. The changing gap causes the magnetic field near the sensor to change. The change in the magnetic field cause the voltage from the sensor to change.
When the crankshaft position sensor (POS) system becomes inoperative, the camshaft position sensor provides various controls of engine parts instead, utilizing timing of cylinder identification signals.

GMC Technical Service Bulletins for P0340 code