Circuit Description
The camshaft position (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, a low reference, and a signal circuit.
The CMP sensor determines whether a cylinder is on a firing stroke or on an exhaust stroke. When the camshaft rotates, the reluctor wheel interrupts a magnetic field that is produced by a magnet within the sensor. The sensor's internal circuitry detects this condition, and produces a signal which the PCM reads. The PCM uses this 1X signal in combination with the Crankshaft Position sensor (CKP) 24X signal in order to determine the crankshaft position and the stroke. This diagnostic monitors 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 in order to determine if the cylinder at top dead center is on the firing stroke, or on the exhaust stroke. The system attempts synchronization, and looks for an increase in the engine speed, indicating that the engine started. If the PCM does not detect an increase in the engine speed, the PCM assumes an incorrect synchronization 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 that the cam signal is stuck low when the signal should be high 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 may cause this DTC to set:
| • | Camshaft reluctor wheel damage |
| • | The sensor coming in contact with the reluctor wheel |
For an intermittent condition, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step verifies that the fault is present.
-
If the duty cycle is present at the PCM connector, the CMP sensor 12-volt reference circuits and the low reference circuits are OK.
-
This step tests the CMP sensor 12-volt reference circuit.
-
This step tests the CMP sensor low reference circuit.
-
This step tests for a short to B+ on the CMP sensor signal circuit.
-
This step tests for a short to ground on the camshaft position sensor signal circuit.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Does the scan tool parameter increment? | -- | Go to Step 3 | Go to Step 4 | |
3 |
Does the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids |
Does the DMM display a duty cycle within the specified range? | 45-55% | Go to Step 17 | Go to Step 5 | |
Does the DMM display the specified voltage? | B+ | Go to Step 6 | Go to Step 8 | |
Use the DMM in order to measure the voltage from the CMP sensor 12-volt reference circuit to the CMP sensor low reference circuit. Does the DMM display the specified voltage? | B+ | Go to Step 9 | Go to Step 7 | |
7 | Test for an open in the CMP sensor low reference circuit. Refer to Testing for Continuity in Wiring Systems. Did you find an open low reference circuit? | -- | Go to Step 13 | Go to Step 17 |
8 | Test for an open or a short to ground in the CMP sensor 12-volt reference circuit. Refer to Circuit Testing in Wiring Systems. Did you find the circuit open or shorted to a ground? | -- | Go to Step 12 | Go to Step 17 |
Is the voltage less than the specified value? | 1 V | Go to Step 10 | Go to Step 14 | |
Probe the CMP signal circuit with the test lamp connected to battery voltage. Does the test lamp illuminate? | -- | Go to Step 15 | Go to Step 11 | |
11 |
Is the resistance less than the specified value? | 2 ohms | Go to Step 18 | Go to Step 16 |
12 | Repair the open or short to ground in the CMP sensor 12-volt reference circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 20 | -- |
13 | Repair the open in the CMP sensor low reference circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 20 | -- |
14 | Repair the short to voltage on the CMP sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 20 | -- |
15 | Repair the short to ground in the CMP sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 20 | -- |
16 | Repair the open in the CMP sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 20 | -- |
17 |
Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 19 |
18 | Replace the CMP position sensor. Refer to Camshaft Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 20 | -- |
19 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 20 | -- |
20 |
Does the DTC run and pass? | -- | Go to Step 21 | Go to Step 2 |
21 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
