GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0340: Camshaft Position (CMP) Sensor Circuit

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

5-Volt Reference Circuit

P0107, P0452, P0522, P0532, P0641

P0340

P0641

--

CMP Sensor Signal Circuit

P0340

P0340

P0340

P0341

Low Reference Circuit

--

P0340

P0340

--

Circuit/System Description

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 2 narrow and 2 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.

Conditions for Running the DTC

    • DTC P0335, P0336, P0641, or P0651 is not set.
    • The engine is cranking or running.
    • The mass air flow (MAF) is greater than 3 grams per second.
    • The DTC runs continuously when the above conditions are met.

Conditions for Setting the DTC

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.

    • The ECM detects that the starter is commanded ON and the engine has been cranking for more than 4 seconds without a CMP sensor pulse.
    • The ECM detects that the engine has started, but did not receive a CMP sensor pulse during the first engine revolution.
    • The ECM detects that the engine is running, but does not receive a CMP sensor pulse for 800 of 1000 engine cycles.

Action Taken When the DTC Sets

    • DTC P0340 is a Type B DTC.
    • The CMP actuator, if equipped, is commanded to the Park position.
    • The ignition system defaults to a failed CMP sensor limp-home mode.

Conditions for Clearing the DTC

DTC P0340 is a Type B DTC.

Diagnostic Aids

    • With a DTC set, the engine may crank for an extended period of time during start-up.
    • This test procedure requires that the vehicle battery has passed a load test and is completely charged. Refer to Battery Inspection/Test.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Electronic Ignition (EI) System Description

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Special Tools

J 35616-A/BT-8637 Connector Test Adapter Kit

Circuit/System Verification

  1. Ignition OFF, open the hood to disable the Auto-Stop function. Refer to Hybrid Modes of Operation Description.
  2. Ignition ON, verify the scan tool hood position parameter displays Open.
  3. If the hood position does not display Open, refer to Diagnostic Trouble Code (DTC) List - Vehicle for DTC P254F.
  4. Ignition OFF, inspect the engine wiring harness carrying the CMP sensor circuits for the following conditions:
  5. • Close routing of aftermarket electrical equipment
    • Close to solenoids, motors, and relays
    If any of these are determined to be a possible source of electrical interference, correct any wire harness routing or component placement conditions.
  6. Start the engine. Using the Live Plot function on the scan tool, select the CMP sensor parameter. Change the minimum spec to 400, and the maximum spec to 4,000 RPM. Select the CKP sensor parameter. Change the minimum spec to 600, and the maximum spec to 3,300 RPM.
  7. Observe the scan tool.
  8. Quickly accelerate and release the accelerator pedal several times. Do not accelerate past 3,200 RPM. The graphed lines on the Live Plot display should track together across the screen.
  9. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

  1. Ignition OFF, open the hood to disable the Auto-Stop function. Refer to Hybrid Modes of Operation Description.
  2. Ignition ON, verify the scan tool hood position parameter displays Open.
  3. If the hood position does not display Open, refer to Diagnostic Trouble Code (DTC) List - Vehicle for DTC P254F.
  4. Ignition OFF, disconnect the harness connector at the CMP sensor.
  5. Test for less than 3 ohms on the CMP low reference circuit, terminal B, and ground.
  6. If greater than the specified value, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  7. Ignition ON, test for 4.8-5.2 volts between the CMP 5-volt reference circuit, terminal A and ground.
  8. 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.
  9. Ignition ON, test for 4.8-5.2 volts between the CMP signal circuit terminal C and ground.
  10. 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.
  11. Ignition OFF, connect a fused jumper wire to the CMP signal circuit terminal C.
  12. Ignition ON, momentarily touch the other end of the fused jumper wire to the battery negative post. The CMP active counter should increment.
  13. If the CMP active counter increments, test or replace the CMP sensor.
    If the CMP active counter does not increment, replace the ECM.

Component Testing

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

  1. Ignition OFF, open the hood to disable the Auto-Stop function. Refer to Hybrid Modes of Operation Description.
  2. Ignition ON, verify the scan tool hood position parameter displays Open.
  3. If the hood position does not display Open, refer to Diagnostic Trouble Code (DTC) List - Vehicle for DTC P254F.
  4. Inspect the CMP sensor for correct installation. Remove the CMP sensor from the engine and inspect the sensor O-ring for damage.
  5. If the sensor is loose, incorrectly installed, or damaged, replace the CMP sensor.
  6. Connect the CMP sensor harness connector to the CMP sensor.
  7. Ignition ON, engine OFF, observe the CMP Active counter parameter on the scan tool.
  8. 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.
  9. If the parameter does not increment, replace the CMP sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Camshaft Position Sensor Replacement
    •  Engine Control Module Replacement
    •  Engine Control Module Programming and Setup