The 4X camshaft position (CMP) sensor circuits consist of an engine control module (ECM) supplied 5-volt reference circuit, low reference circuit, and an output signal circuit. The CMP sensor is an internally magnetic biased digital output integrated circuit sensing device. The sensor detects magnetic flux changes between the peaks and valleys of a 4-tooth reluctor wheel attached to the camshaft. As each reluctor wheel tooth rotates past the CMP sensor, the resulting change in the magnetic field is used by the sensor electronics to produce a digital output pulse. The sensor returns a digital ON/OFF DC voltage pulse of varying frequency, with two narrow, and two wide output pulses per camshaft revolution that represent an image of the camshaft reluctor wheel. The frequency of the CMP sensor output depends on the velocity of the camshaft. The ECM decodes the narrow and wide tooth pattern to identify camshaft position. This information is then used to sequence the ignition timing and fuel injection events for the engine. The ECM also uses CMP sensor output information to determine the camshaft relative position to the crankshaft, to control the CMP actuator if equipped, and for limp-home operation.

Important: Important: The ECM detects engine movement by sensing the airflow through the MAF sensor, when airflow is greater than 3 grams per second, or by sensing crankshaft position (CKP) sensor pulses.

DTC P0340 is a Type B DTC.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Description and Operation

Electronic Ignition (EI) System Description

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

1. Ignition OFF, inspect the engine wiring harness carrying the CMP sensor circuits for the following conditions:

•	Close routing of aftermarket electrical equipment

•	Close to solenoids, motors, and relays

⇒	Correct any wire harness routing or component placement conditions, if it is determined to be a possible source of electrical interference.

2. Start the engine. Using the live plot function on the scan tool, select the CMP sensor parameter. Change the minimum spec to 400 RPM, and the maximum spec to 4,000 RPM. Select the CKP sensor parameter. Change the minimum spec to 600 RPM, and the maximum spec to 3,300 RPM.
3. Observe the scan tool.
4. Quickly accelerate and release the accelerator pedal several times. Do not accelerate pass 3,200 RPM. The graphed lines on the live plot display should track together across the screen.
5. Operate the Vehicle within the Conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records data list.

Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

1. Ignition OFF, disconnect the harness connector at the CMP sensor.
2. Test for less than 1 ohm of resistance on the CMP low reference circuit terminal C and ground.

⇒	If greater than the specified value, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, test for 4.8-5.2 volts between the CMP 5-volt reference circuit terminal A and ground.

⇒	If less than the specified range, test the 5-volt reference circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.

⇒	If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Ignition ON, test for 4.8-5.2 volts between the CMP signal circuit terminal B and ground.

⇒	If less than the specified range, test the signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.

⇒	If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

5. Ignition OFF, connect a fused jumper wire to the CMP signal circuit terminal C.
6. Ignition ON, momentarily touch the other the other end of the fused jumper wire to the battery negative post. The CMP Active counter, should increment.

⇒	If the CMP Active counter increments, test or replace the CMP sensor.

⇒	If the CMP Active counter does not increment, replace the ECM.

Important: You must perform the Circuit/System Testing before proceeding with Component Testing.

1. Inspect the CMP sensor for correct installation. Remove the CMP sensor from the engine and inspect the sensor O-ring for damage.

⇒	If the sensor is loose, incorrectly installed, or damaged, replace the CMP sensor.

2. Connect the CMP sensor harness connector to the CMP sensor.
3. Ignition ON, engine OFF. Observe the CMP Active counter parameter on the scan tool.
4. Pass a flat steel object across the tip of the sensor repeatedly. The CMP Active counter parameter should increment with each pass of the steel object.

⇒	If the parameter does not increment, replace the CMP sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.