Description & Operation
The Camshaft Position (CMP) sensor provides camshaft position information that is used by the ECM for fuel and ignition system synchronization. The sensor is a Hall effect digital sensor. It has a metal pulse ring and a pickup assembly located inside the distributor. The CMP signal is a digital on/off type signal. When the pulse ring travels through the pickup, a permanent magnet inside the pickup creates magnetism, which induces voltage. The pulse ring has slots, or one large slot; as the slot(s) pass, the pickup loses its magnetism and voltage is lost, thereby generating the on/off signal. The CMP and Crankshaft Position (CKP) sensor let the ECM know the position of the camshaft and crankshaft, so the engine can be properly timed.
- Remove the engine cover.
- With the DRB-II scan tool or equivalent, plug in to diagnostic connector.
- Using the DRB-II, erase all DTCs and turn the ignition off and on again.
- Crank the engine and observe CAM SYNC; if NO CAM SYNC is shown, proceed to the next step. If CAM SYNC was present, the CMP sensor is operational.
- Inspect the wiring and connectors, repair as necessary and retest or if OK, proceed to next step.
- Unplug the CMP sensor connector.
- Turn the ignition ON and, using a voltmeter, probe the CMP connector to verify the supply voltage using supplied wiring schematic.
- On 1995 and earlier vehicles, if voltage is 7.0v or above, proceed to the next step; if no voltage or insufficient voltage is detected, repair the circuit and retest.
- On 1996-98 vehicles, the voltage should be 4.5v or above. If voltage does not met specifications, repair circuit and retest, if OK, proceed to next step.
- Connect a jumper between the CMP signal circuit and CMP ground circuit (use supplied schematic). Without turning key off, attempt to start vehicle while making and breaking connection. If vehicle starts, replace CMP sensor. If vehicle does not start proceed to next step.
- Remove the distributor cap and ensure that distributor turns while cranking engine. If distributor turns, proceed to next step, if it does not turn, repair as necessary and retest.
- Disconnect the negative battery cable.
- Using an ohmmeter, probe the ground circuit between the CMP sensor connector and a engine ground. If resistance is less than 5.0 ohms, proceed to next step, if not, repair circuit and retest.
- Disconnect the ECM wiring harness.
- Using an ohmmeter, test the CMP signal circuit for resistance between the CMP sensor connector and the ECM harness connector. If resistance is less than 5.0 ohms, proceed to next step, if not, repair circuit and retest.
- Using an ohmmeter measure the CMP signal circuit resistance between CMP connector and ground, if resistance is less than 5.0 ohms, repair the CMP signal circuit for a short ground. If the resistance is more than 5.0 ohms, replace the ECM.
Install the engine cover. Connect the negative battery cable.