GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The camshaft position (CMP) sensor works in conjunction with the 1X reluctor trigger wheel on the front of the camshaft gear. The engine control module (ECM) provides a 12-volt reference to the CMP sensor, as well as a low reference and a signal circuit. As the camshaft gear rotates, the reluctor trigger wheel interrupts a magnetic field produced by a magnet within the sensor. The CMP sensor internal circuitry detects this interruption of the magnetic field and produces a signal, which the ECM reads. The 1X signal produced by the CMP sensor is used by the ECM to determine if the cylinder at the top dead center (TDC) is on the firing stroke or the exhaust stroke. The ECM can determine TDC for all cylinders by using the crankshaft position (CKP) sensor 24X signal. If the 1X signal is not received by the ECM, a slightly longer cranking time may be experienced. The ECM will attempt synchronization and looks for an increase in engine speed, indicating that the engine is running. If the ECM does not detect an increase in engine speed, the ECM assumes that it incorrectly synchronized to the exhaust stroke, and then will synchronize to the opposite cam position. If the ECM detects that there is no output signal from the CMP sensor, DTC P0340 will set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0340 Camshaft Position (CMP) Sensor Circuit

Conditions for Running the DTC

    • The engine is cranking, or the engine is running.
    • DTC P0340 runs continuously when the above condition is met.

Conditions for Setting the DTC

The ECM detects no CMP sensor output for more than 3 seconds.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores the information in the Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

    • The control module turns OFF the MIL after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC last test failed clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles if no failures are reported by this or any other emission related diagnostic.

Test Description

The number below refers to the step number on the diagnostic table.

  1. The test lamp in this step is used to apply a load to the 12-volt reference circuit of the CMP sensor.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Start and idle the engine.
  2. Monitor the camshaft position (CMP) sensor active counter parameter with a scan tool.

Does the CMP sensor active counter number increment?

--

Go to Intermittent Conditions

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the CMP sensor electrical connector.
  3. Test for shorted terminals and poor connections at the CMP sensor wire harness electrical connector and the mating electrical connector on the CMP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 4

4

  1. Turn ON the ignition, with the engine OFF.
  2. Connect a jumper wire to the 12-volt reference circuit at the CMP sensor wire harness electrical connector.
  3. Connect a test lamp between the jumper wire and a good ground.
  4. Connect the positive lead of the DMM to the junction of the jumper wire and test lamp.
  5. Connect the negative lead of the DMM to a good engine ground.
  6. Measure the voltage from the 12-volt reference circuit to a good ground with a DMM. Refer to Circuit Testing .

Is the voltage within the specified range?

10-13 V

Go to Step 5

Go to Step 6

5

  1. Remove the test lamp from the jumper wire.
  2. Connect another jumper wire to the signal circuit of the CMP sensor wire harness electrical connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Monitor the CMP active counter parameter with a scan tool.
  5. Momentarily connect the two ends of the jumper wires together several times.

Does the CMP sensor active counter number increment?

--

Go to Step 10

Go to Step 7

6

Test the CMP 12-volt reference circuit between the CMP sensor and the engine control module (ECM) for the following conditions:

    • An open
    • High resistance
    • A short to ground

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

7

Test the CMP low reference circuit between the CMP sensor and the ECM for the following conditions:

    • An open
    • High resistance
    • A short to ground
    • A short to voltage

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 8

8

Test the CMP signal circuit between the CMP sensor and the ECM for the following conditions:

    • An open
    • High resistance
    • A short to ground
    • A short to voltage

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

9

Test for shorted terminals and poor connections at the ECM wire harness electrical connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 11

10

Replace the CMP sensor. Refer to Camshaft Position Sensor Replacement .

Did you complete the replacement?

--

Go to Step 12

--

11

Replace the ECM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 12

--

12

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. 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.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 13

13

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK