See Figure 1
The Camshaft Position Sensor, or CMP sensor is located inside the distributor. The PCM uses the CMP signal to determine the position of the No. 1 cylinder piston during its power stroke. The PCM uses this information in conjunction with the crankshaft position sensor to determine spark timing among other things.
The CMP sensor contains a Hall effect device which sends either a 0.0 volt or a 5.0 volt signal to the PCM depending on the position of the distributor shaft.
If the cam signal is lost while the engine is running, the PCM will calculate spark timing based on the last CMP signal and the engine will continue to run. However, the engine will not run after it is shut off.
- Make sure that the ignition is OFF , remove the distributor cap and turn the engine over by hand.
- Verify that the distributor shaft turns. If the distributor shaft does not turn, the engine must be checked for proper mechanical operation.
- Backprobe with a high impedance ohmmeter between the CMP sensor connector middle terminal and battery ground.
- Verify that the resistance is less than 5 ohms. If the resistance is not as specified, repair or replace the wiring as necessary and continue the test.
- With the ignition ON and the engine OFF , backprobe with a high impedance voltmeter between the sensor connector middle terminal and either of the end terminals.
- Verify that a 5 volt or greater signal is present at one of the two terminals. If not as specified, repair or replace the wiring as necessary and continue the test.
- With the ignition ON and the engine OFF , backprobe with a high impedance voltmeter between the sensor connector middle terminal and the end terminal that did not have the 5 volt or greater signal.
- Crank the engine by hand and verify that the voltage reading alternates between 0.0 or 5.0 volts.
- Install the distributor cap and crank the engine with starter. Verify that the voltage reading is 2.5 volts (averaging voltmeters only).
- If the voltage readings are not as specified, the sensor may be faulty.
Removal & Installation
- Disconnect the negative battery cable and remove the intake air tube if necessary.
- Remove the distributor cap and the rotor.
- Disengage the CMP sensor wiring connector and carefully lift the sensor out of the distributor.
- Carefully place the sensor into the distributor. Make sure that any alignment notches or tabs line up properly.
- Install the distributor rotor and cap.
- Engage the sensor wiring connector and connect the negative battery cable.