Circuit Description
The camshaft position (CMP) sensor is a sensor designed to detect changes in a magnetic field. The control module supplies the CMP sensor with the following circuits:
| • | A 12-volt reference circuit |
| • | A low reference circuit |
| • | A signal circuit |
The CMP sensor produces a magnetic field whenever the ignition is ON. The CMP sensor is mounted near a reluctor wheel that is attached to the distributor shaft. When the distributor shaft rotates, or when the engine is cranking or running, the reluctor wheel changes the magnetic field. The CMP sensor converts each change in the magnetic field into a PULSE. The number of teeth on the reluctor wheel determines how many pulses the CMP sensor detects per camshaft rotation. The control module uses the CMP sensor signal in order to calculate the correct timing for sequential fuel injection (SFI). If the powertrain control module (PCM) does not detect the CMP signal while the engine is running, this diagnostic trouble code (DTC) will set.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
The CMP sensor reference pulse is not detected once every 2 crankshaft revolutions.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles. |
| • | The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records. |
Conditions for Clearing the MIL or DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed. |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool in order to clear the DTCs. |
Diagnostic Aids
If the condition is intermittent, refer to Intermittent Conditions .
Electromagnetic interference (EMI) from the ignition coil or from the spark plug wires could cause a faulty signal condition in the CMP signal circuit to the PCM. Ensure that the routing of the CMP circuitry is correct.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
The CAM signal on the scan tool should change each time the signal circuit is touched.
-
If the fuse opens in the jumper wire, there is a short to ground on the 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 | |
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 |
4 |
Does the voltage measure near the specified value? | B+ | Go to Step 6 | Go to Step 5 |
5 |
Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 12 |
6 |
Does the test lamp illuminate? | -- | Go to Step 8 | Go to Step 7 |
7 |
Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 12 |
Does the cam signal high to low and low to high parameter change EACH time the signal circuit is touched? | -- | Go to Step 14 | Go to Step 9 | |
Did the fuse in the jumper wire open? | -- | Go to Step 11 | Go to Step 10 | |
10 | Test the signal circuit of the CMP sensor for a short to voltage or an open or high resistance. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 12 |
11 | Test the signal circuit of the CMP sensor for a short to ground. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 12 |
12 | Inspect for poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 13 |
13 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- |
14 | Inspect for poor connections at the CMP sensor. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 15 |
15 | Replace the CMP sensor. Refer to Camshaft Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- |
16 |
Does the DTC run and pass? | -- | Go to Step 17 | Go to Step 2 |
17 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
