GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The camshaft position (CMP) sensor provides the powertrain control module (PCM) with a signal representing the camshaft's rotational position. The CMP sensor is a hall effect switch that works in conjunction with a 4X reluctor wheel. The reluctor wheel consists of 4 pairs of rising and falling edges that are differently spaced. The CMP sensor produces a magnetic field. When the camshaft rotates, and the reluctor wheel edge passes by the CMP sensor, there is a change in the magnetic field. The PCM views each transition from low to high as one signal. The PCM receives 4 signals per camshaft revolution. The CMP sensor has the following circuits:

    • A 5-volt circuit
    • A low reference circuit
    • A signal circuit

The PCM supplies 5 volts to the CMP sensor on the 5-volt reference circuit, and provides a low reference circuit. The CMP sensor provides a 4X signal to the PCM on the signal circuit. If the PCM detects extra or missing CMP sensor signal transitions within a certain number of crankshaft revolutions, 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

    • DTCs P0106, P0107, P0108, P0315, P0335, and P0336 are not set.
    • The engine is running.
    • The manifold absolute pressure (MAP) is more than 45 kPa.
    • This DTC runs continuously.

Conditions for Setting the DTC

The PCM does not detect the signal of the CMP sensor for 3 seconds.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

    • The control module turns OFF the malfunction indicator lamp (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.
    • Clear the MIL and the DTC with a scan tool.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

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

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Start the engine.
  2. Observe the CMP Sensor parameter on the scan tool.

Does the CMP Sensor parameter increment?

--

Go to Step 3

Go to Step 4

3

  1. Observe the Freeze Frame/Failure Records for this DTC.
  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 4

Go to Testing for Intermittent Conditions and Poor Connections

4

  1. Turn OFF the ignition.
  2. Disconnect the harness connector of the camshaft position (CMP) sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the 5-volt reference circuit to the low reference circuit of the CMP sensor with a DMM.

Is the voltage within the specified range?

4.8-5.2 V

Go to Step 7

Go to Step 5

5

Measure the voltage from the 5-volt reference circuit of the CMP sensor to a good ground.

Is the voltage within the specified range?

4.8-5.2 V

Go to Step 6

Go to Step 11

6

Measure the resistance of the low reference circuit of the CMP sensor with a DMM. Refer to Circuit Testing .

Is the resistance less than the specified value?

5 ohms

Go to Step 8

Go to Step 12

7

Measure the resistance of the 5-volt reference circuit of the CMP sensor with a DMM. Refer to Circuit Testing .

Is the resistance less than the specified value?

5 ohms

Go to Step 8

Go to Step 11

8

  1. Observe the CMP active counter parameter with a scan tool.
  2. Momentarily and repeatedly probe the signal circuit of the CMP sensor with a test lamp connected to battery voltage.

Does the CMP sensor parameter increment?

--

Go to Step 9

Go to Step 13

9

  1. Remove the CMP sensor. Refer to Camshaft Position Sensor Replacement .
  2. Visually inspect the CMP sensor for the following conditions:
  3. • Physical damage
    • Loose or improper installation
    • Wiring routed too close to the secondary ignition components

Did you find and correct the condition?

--

Go to Step 18

Go to Step 10

10

  1. Visually inspect the CMP sensor reluctor ring for damage.
  2. If the CMP reluctor ring is damaged, refer to Camshaft Cleaning and Inspection .

Did you find and correct the condition?

--

Go to Step 18

Go to Step 14

11

Test the 5-volt reference circuit of the CMP sensor for one of the following conditions:

    • An open
    • A short to ground
    • High resistance

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 18

Go to Step 15

12

Test the low reference circuit of the CMP sensor for an open or high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 18

Go to Step 15

13

Test the signal circuit of the CMP sensor for one of the following conditions:

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

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 18

Go to Step 15

14

Test for an intermittent and for a poor connection at 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 18

Go to Step 16

15

Test for an intermittent and for a poor connection at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 18

Go to Step 17

16

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

Did you complete the replacement?

--

Go to Step 18

--

17

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

Did you complete the replacement?

--

Go to Step 18

--

18

  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 19

19

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