GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2002 🢒 DeVille 🢒 DTC 🢒 DTC P0340

Circuit Description

The PCM uses the camshaft position (CMP) sensor high resolution signal in order to determine the position of the valve train in relation to the engine cylinders. The PCM uses the CMP high resolution signal to sequence the ignition system, and the fuel injectors.

The PCM supplies a 12-volt reference and a low reference to the CMP sensor. The CMP sensor returns a signal pulse in response to the reluctor track, located on the camshaft sprocket. If during operation, the PCM detects a loss of CMP sensor high resolution signal, DTC P0340 will set.

Conditions for Running the DTC

No CKP sensor DTCs set with engine running more than 400 RPM.

Conditions for Setting the DTC

The PCM detects a loss of CMP sensor high resolution signal.

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

If the condition is intermittent, refer to Intermittent Conditions .

Ignition system DTCs set with the ignition switch in the START position if the starter relay or the starter is inoperative. When the PCM enables starter operation, the PCM also initiates the diagnostic test routines for DTCs P0335, P0340, and P0385. If a condition exists which prevents the engine from cranking, the PCM will not receive signal input from the CKP and CMP sensors, and the DTCs will set.

If DTC P0615 is set, diagnose DTC P0615 first. If DTC P0335, P0340, and/or P0385 are set and no trouble is found, check for the following:

    • Is there a no-crank condition or an intermittent no-crank condition?
    • Was an attempt made to crank the engine with the shift lever not in P/N?

Test Description

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

  1. This step determines if the 12-volt reference circuit to the CKP A, the CKP B, and the CMP are shorted to a ground. If all 3 DTCs are set, this indicates the circuit is shorted to a ground or a sensor is internally shorted. All 3 DTCs set because the 12-volt reference circuit are internally connected within the PCM. The engine will not start with this condition.

    2.

  2. This step determines if the CMP sensor is shorted internally. If the 12-volt Reference parameter changes from Fault to OK, the condition is with the sensor.

    3.

  3. This step determines if the CKP A sensor is shorted internally. If the 12-volt Reference parameter changes from Fault to OK, the condition is with the sensor.

    4.

  4. This step determines if the CKP B sensor is shorted internally. If the 12-volt Reference parameter changes from Fault to OK, the condition is with the sensor.

Step

Action

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. Attempt to start the engine.
  3. With a scan tool, monitor the DTC information for DTCs P0335, P0340, and P0385.

Are all three DTCs set?

Go to Step 9

Go to Step 3

3
  1. Start the engine.
  2. With a scan tool, monitor the DTC information .

Does the scan tool indicate that DTC P0340 passed?

Go to Intermittent Conditions

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Leave the scan tool installed.
  3. Disconnect the CMP sensor harness connector.
  4. Turn ON the ignition, with the engine OFF.
  5. Connect a test lamp between the CMP sensor 12-volt reference circuit and the low reference circuits.

Does the test lamp illuminate?

Go to Step 6

Go to Step 5

5
  1. Test for the following circuit conditions:
    2. • An open CMP sensor 12-volt reference circuit
    • An open CMP sensor low reference circuit
    • Poor connections at the PCM
  2. If a condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 17

Go to Step 16

6
  1. Turn ON the ignition, with the engine OFF.
  2. Connect test lamp to battery positive voltage.
  3. Observe the CMP sensor data display on the scan tool while repeatedly touching the test lamp to the CMP high resolution signal circuit, in the harness connector.

Does the scan tool indicate an RPM?

Go to Step 8

Go to Step 7

7
  1. Test the CMP sensor high resolution signal circuit for the following conditions:
    2. • An open
    • A short to voltage
    • A short to CMP sensor 12-volt reference circuit
    • A short to ground
    • A short to CMP sensor low reference circuit
    • Poor connections at the PCM
  2. If a condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 17

Go to Step 16

8
  1. Inspect for poor connections at the CMP sensor.
  2. If the condition is found, repair as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 17

Go to Step 13

9

  1. Disconnect the CMP sensor harness connector. Refer to Camshaft Position Sensor Replacement .
  2. With a scan tool, monitor the 12-volt reference parameter.

Does the scan tool display OK?

Go to Step 13

Go to Step 10

10

  1. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  2. Disconnect the CKP A sensor harness connector. Refer to Crankshaft Position Sensor Replacement .
  3. With a scan tool, monitor the 12-volt reference parameter.

Does the scan tool display OK?

Go to Step 14

Go to Step 11

11

  1. Disconnect the CKP B sensor harness connector. Refer to Crankshaft Position Sensor Replacement .
  2. With a scan tool, monitor the 12-volt reference parameter.

Does the scan tool display OK?

Go to Step 15

Go to Step 12

12
  1. Turn OFF the ignition.
  2. Disconnect the PCM harness connectors. Refer to Powertrain Control Module Replacement .
  3. Test the 12-volt reference circuit of the CKP A, the CKP B, and the CMP sensors for a grounded circuit. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 17

--

13

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

Did you complete the replacement?

Go to Step 17

--

14

Replace the CKP A sensor. Refer to Crankshaft Position Sensor Replacement .

Did you complete the replacement?

Go to Step 17

--

15

Replace the CKP B sensor. Refer to Crankshaft Position Sensor Replacement .

Did you complete the replacement?

Go to Step 17

--

16

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 17

--

17

  1. Use the scan tool in order to clear the 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 18

Go to Step 2

18

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