GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The camshaft position (CMP) sensor is a 1X sensor. The CMP provides one digital ON/OFF signal to the powertrain control module (PCM) per revolution of the camshaft. This information is used by the PCM to determine the position of the valve train relative to the crankshaft position (CKP). By monitoring the CMP and CKP signals, the PCM can accurately time the operation of the fuel injectors. The CMP sensor is connected directly to the ignition control module (ICM). The sensor wiring includes the following circuits which are shared with the CKP sensor:

    • The CMP sensor signal circuit
    • A 12-volt reference circuit
    • A low reference circuit

The signal is passed through the ICM to the PCM on the CMP signal circuit. The PCM monitors the CMP sensor for errors. If the PCM does not receive a signal from the CMP sensor, DTC P0340 sets.

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 for more than 3 seconds.
    • This diagnostic runs continuously when either condition is met.

Conditions for Setting the DTC

    • The PCM detects the following for every 2 engine revolutions:
       - Thirty six medium resolution engine speed signals
       - Six low resolution engine speed signals
       - Zero CMP signals
    • The condition exists for more than 4 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.

Diagnostic Aids

Inspect for the following conditions:

    • Any secondary ignition wires arcing to a wiring harness and for carbon tracking or other signs of damage
    • A faulty ignition coil
    • The ICM and the coils for cracks, carbon tracking, or other signs that indicate that the coil secondary circuit is arcing to the ICM or to the ICM wiring harness--Refer to Ignition Coil Replacement .

If the condition is suspected of being intermittent, refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This test verifies if the sensor is working correctly. By suppling a ground to the circuit, the voltage should change when the circuit is touched with a test lamp.

  2. This step determines if the fault is caused by a missing camshaft magnet or by a faulty PCM. The voltage measured in this step should be near 5 volts, and decrease to near 0 volts when the CMP sensor interfaces with the camshaft magnet.

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?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Attempt to start the engine.

Does the engine start and run?

--

Go to Step 3

Go to Step 4

3

  1. Turn OFF the ignition for 30 seconds.
  2. Start the engine.
  3. 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 Diagnostic Aids

4

  1. Turn OFF the ignition.
  2. Disconnect the powertrain control module (PCM).
  3. Turn ON the ignition, with the engine OFF.
  4. Important: If voltage measures 0 volts, rotate the crankshaft to ensure the camshaft position (CMP) sensor magnet is not located under the CMP sensor at the time of the test.

  5. Measure the voltage from the CMP signal circuit at the PCM connector to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the voltage within the specified range?

4.5-5.5 V

Go to Step 8

Go to Step 5

5

Does the voltage on the CMP signal circuit measure more than the specified value?

5 V

Go to Step 17

Go to Step 6

6

Probe the CMP signal circuit at the PCM connector with a test lamp that is connected to battery voltage. Refer to Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 16

Go to Step 7

7

  1. Disconnect the ignition control module (ICM).
  2. Measure the resistance of the CMP signal circuit between the ICM and the PCM with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the resistance within the specified value?

0-5 ohms

Go to Step 8

Go to Step 15

8

  1. Turn OFF the ignition.
  2. Remove the CMP sensor from the engine front cover without disconnecting the CMP sensor harness connector. Refer to Camshaft Position Sensor Replacement .
  3. Important: The magnet used must have sufficient power and the correct polarity. If the voltage remains at 5 volts, retest using the opposite end of the magnet.

  4. Turn ON the ignition, with the engine OFF.
  5. Place a magnet on the CMP sensor.
  6. Measure the voltage from the CMP signal circuit at the PCM connector to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Does the voltage toggle from 5 volts to 0 volts when the magnet is moved across the sensor surface?

--

Go to Step 25

Go to Step 9

9

  1. Turn OFF the ignition.
  2. Install the CMP sensor to the engine front cover.
  3. Disconnect the CMP sensor.
  4. Turn ON the ignition, with the engine OFF.
  5. Probe the 12-volt reference circuit of the CMP sensor with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 10

Go to Step 18

10

  1. Turn OFF the ignition.
  2. Disconnect the ICM.
  3. Measure the resistance of the low reference circuit from the CMP sensor connector to the ICM connector with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the resistance within the specified value?

0-5 ohms

Go to Step 11

Go to Step 19

11

  1. Connect the ICM.
  2. Turn ON the ignition, with the engine OFF.
  3. Measure the voltage from the CMP sensor signal circuit of the CMP sensor to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the voltage less than the specified value?

7 V

Go to Step 12

Go to Step 22

12

  1. Turn OFF the ignition.
  2. Disconnect the ICM.
  3. Measure the resistance of the CMP sensor signal circuit from the CMP sensor connector to the ICM connector with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the resistance within the specified range?

0-5 ohms

Go to Step 13

Go to Step 20

13

  1. Connect the ICM.
  2. Turn ON the ignition, with the engine OFF.
  3. Probe the CMP sensor signal circuit of the CMP sensor with a test lamp that is connected to battery voltage. Refer to Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 21

Go to Step 14

14

  1. Connect the ICM.
  2. Disconnect the PCM.
  3. Turn ON the ignition, with the engine OFF.
  4. Momentarily and repeatedly probe the CMP sensor signal circuit with a test lamp that is connected to a good ground.
  5. Measure the voltage on the camshaft position signal circuit at the PCM connector to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Does the voltage change when the circuit is touched?

--

Go to Step 24

Go to Step 23

15

Repair the open in the CMP signal circuit between the ICM and the PCM. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 31

--

16

Test the CMP signal circuit between the ICM and the PCM for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 31

Go to Step 23

17

Test the CMP signal circuit between the ICM and the PCM for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 31

Go to Step 23

18

Test the CMP 12-volt reference circuit between the CMP sensor and the ICM for an open, high resistance, or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 31

Go to Step 23

19

Repair the open or high resistance in the low reference circuit between the CMP sensor and the ICM. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 31

--

20

Repair the open or high resistance in the CMP sensor signal circuit between the CMP sensor and the ICM. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 31

--

21

Test the CMP sensor signal circuit between the CMP sensor and the ICM for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 31

Go to Step 23

22

Test the CMP sensor signal circuit between the CMP sensor and the ICM for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 31

Go to Step 23

23

Test for an intermittent and for a poor connection at the ICM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 31

Go to Step 27

24

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 in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 31

Go to Step 28

25

Test for an intermittent and for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 31

Go to Step 26

26

  1. Install the CMP sensor to the engine front cover. Refer to Camshaft Position Sensor Replacement .
  2. Measure the voltage of the CMP signal circuit at the PCM connector to ground with a DMM. Refer to Circuit Testing in Wiring Systems.
  3. Observe the voltage while repeatedly bumping the engine with the starter.

Does the voltage toggle from 5 volts to 0 volts while bumping the engine with the starter?

--

Go to Step 29

Go to Step 30

27

Replace the ICM. Refer to Ignition Control Module Replacement .

Did you complete the replacement?

--

Go to Step 31

--

28

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

Did you complete the replacement?

--

Go to Step 31

--

29

Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 31

--

30

Replace a faulty or missing CMP sensor magnet on the camshaft sprocket.

Did you complete the replacement?

--

Go to Step 31

--

31

  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 32

32

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 in Vehicle DTC Information

System OK