GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 DTC P0343

Circuit Description

The CMP sensor works in conjunction with a 1X reluctor wheel on the camshaft. The powertrain control module (PCM) provides a 12 volt reference to the CMP sensor as well as a low reference and a signal circuit.

The CMP sensor determines whether a cylinder is on a firing stroke or on an exhaust stroke. As the camshaft rotates, the reluctor wheel interrupts a magnetic field produced by a magnet within the sensor. The sensors internal circuitry detects this and produces a signal which the PCM reads. The PCM uses this 1X signal in combination with the crankshaft position (CKP) sensor 24X signal in order to determine crankshaft position and stroke. This diagnostic for the CMP sensor checks for a loss of CMP sensor signal.

As long as the PCM receives the CKP sensor 24X signal, the engine will start. The PCM can determine top dead center for all cylinders by using the CKP sensor 24X signal alone. The CMP sensor 1X signal is used by the PCM to determine if the cylinder at top dead center is on the firing stroke, or the exhaust stroke. The system attempts synchronization and looks for an increase in engine speed indicating the engine started. If the PCM does not detect an increase in engine speed, the PCM assumes it incorrectly synchronized to the exhaust stroke and re-syncs to the opposite cam position. A slightly longer cranking time may be a symptom of this condition.

Conditions for Running the DTC

The engine speed is less than 4,000 RPM.

Conditions for Setting the DTC

The PCM detects the CAM signal is stuck high when the signal should be low for 1.5 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

The following conditions may cause this DTC to set:

    • Camshaft reluctor wheel damage
    • The sensor coming in contact with the reluctor wheel

Using Freeze Frame and Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and Failure Records data can aid in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also aid determining how many ignition cycles the diagnostic reported a pass or a fail. Operate the vehicle within the same Freeze Frame conditions such as RPM, load, vehicle speed, temperature, etc. that you observed. This will isolate when the DTC failed.

The CMP sensor output can be tested. The sensor must be supplied with a power and a ground. The engine must be cranking to perform this test. You can measure the duty cycle at the signal circuit of the sensor. The duty cycle should be between 45-55 percent for a good sensor.

If the condition is intermittent, refer to Intermittent Conditions .

Test Description

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

  1. This step verifies that the fault is present. A hard start is observed when a malfunction is present.

    2.

  2. This step tests the CMP sensor 12 volt reference circuit from the PCM to the CMP.

    3.

  3. This step tests the CMP sensor low reference circuit from the PCM to the CMP.

    4.

  4. This step tests the CMP sensor signal circuit. Applying a voltage causes the CMP signal input high-to-low and low-to-high parameter to increase if the circuit and the PCM are operating properly.

    5.

  5. This step tests the resistance of the CMP sensor 12 volt reference circuit from the PCM to the CMP sensor.

    6.

  6. This step tests the resistance of the CMP sensor low reference circuit from the PCM to the CMP sensor.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Connect a scan tool.
  2. Start the engine.
  3. Use the scan tool in order to monitor the CMP signal input high-to-low and low-to-high transition parameter.

Does the scan tool parameter increment?

--

Go to Step 3

Go to Step 4

3
  1. Observe the Freeze Frame and Failure Records for this DTC.
  2. Turn the ignition OFF for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as closely as possible to the conditions recorded in the Freeze Frame and Failure Records.

Does the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4

  1. Turn OFF the ignition.
  2. Disconnect the CMP sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Use a digital multimeter (DMM) connected to battery ground in order to measure the voltage on the CMP sensor 12 volt reference circuit.

Is the voltage near the specified value?

B+

Go to Step 5

Go to Step 7

5

Use the DMM in order to measure the voltage from the CMP 12 volt reference circuit to the CMP low reference circuit.

Is the voltage near the specified value?

B+

Go to Step 6

Go to Step 9

6

  1. Start the engine.
  2. Use the scan tool in order to monitor the CMP signal high-to-low and low-to-high transition.
  3. Use a test lamp connected to B+ in order to momentarily and repeatedly probe the signal circuit.

Does the CMP signal high to low, low to high transition counters increment when the test lamp contacts the signal circuit?

--

Go to Step 15

Go to Step 10

7

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C2 located on the opposite side of the manufacturer's logo. Refer to Powertrain Control Module Replacement .
  3. Use the DMM in order to measure the resistance of the CMP 12 volt reference circuit. Refer to Circuit Testing in Wiring Systems.

Is the resistance within the specified range?

0-5 ohms

Go to Step 8

Go to Step 12

8

Test the CMP 12 volt reference circuit for the following conditions:

    • A grounded circuit
    • A poor connection

Did you find and correct the condition?

--

Go to Step 19

Go to Step 16

9

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C1 located on the same side as the manufacturer's logo. Refer to Powertrain Control Module Replacement .
  3. Use the DMM in order to measure the resistance on the CMP low reference circuit. Refer to Circuit Testing in Wiring Systems.

Is the resistance within the specified range?

0-5 ohms

Go to Step 16

Go to Step 13

10
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C1 located on the same side as the manufacturer's logo. Refer to Powertrain Control Module Replacement .
  3. Use the DMM in order to measure the resistance of the CMP signal circuit. Refer to Circuit Testing in Wiring Systems.

Is the resistance within the specified range?

0-5 ohms

Go to Step 11

Go to Step 14

11
  1. Turn ON the ignition, with the engine OFF.
  2. Test the CMP signal circuit for the following conditions:
    3. • A grounded circuit
    • A circuit shorted to voltage

Did you find and correct the condition?

--

Go to Step 19

Go to Step 16

12
  1. Inspect the CMP 12 volt reference circuit for an open.
  2. If you find an open, repair the circuit. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 16

13

Repair an open in the CMP low reference circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 19

--

14

Repair an open in the CMP signal circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 19

--

15
  1. Inspect for poor connections at the CMP harness connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. If you find a poor connection, repair the connector as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 17

16
  1. Inspect the PCM harness connector for poor connections. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. If you find a poor connection, repair the connector as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 18

17

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

Did you complete the replacement?

--

Go to Step 19

--

18

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 19

--

19
  1. Use the scan tool in order to clear any DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 20

Go to Step 2

20

With a scan tool observe the Stored Information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK