GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

Camshaft Position Sensor

Print

The 3.1L Engine uses a Distributor.

OPERATION



During cranking, the Ignition control Module (ICM) monitors the 7X-crankshaft (3.4L Engine) position sensor signal. Once the ICM determines spark synchronization, 3X reference signals are sent to the PCM. The PCM will command all six injectors ON for one priming shot of fuel in all cylinders. After the priming, the injectors are left OFF for the next six fuel control reference signals (two crankshaft revolutions). This allows each cylinder a chance to use the fuel from the priming shot. During this waiting period, a cam pulse will have been received by the PCM. The PCM uses the Cam signal pulses to initiate sequential fuel injection. The PCM constantly monitors the number of pulses on the Cam signal circuit and compares the number of Cam pulses to the number of 24X reference pulses and the number of 3X reference pulses being received. If the PCM receives and incorrect number of pulses on the Cam reference circuit, the PCM will initiate injector sequence without the Cam signal with a one in six chance that injector sequence is correct. The engine will continue to start and run normally, although the misfire diagnostic will be affected if a misfiring condition occurs. It will also set a DTC.

TESTING



3.8L Engine

Diagnostic Aids-check for:



Incorrect harness routing near secondary ignition components.
 
Ignition coil arcing to the wiring harness or to the Ignition Control Module. Check the ignition coils for cracks, carbon tracking, or other signs of damage.
 
Secondary ignition wire(s) arcing to the wiring harness.
 
Check for a poor connection or damaged harness: Inspect the PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connections and damaged harnesses.
 
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.
 
Perform an intermittent test: If connections and harnesses check OK, monitor a digital voltmeter connected from the PCM terminal "RB9"(cam signal) to ground while moving related connectors and wiring harnesses. If the failure is induced, the voltage reading will change. This may help to isolate the location of the malfunction.
 

If necessary to perform a test on the camshaft sensor, use the diagnostic tree and the connector diagram given here for the 3.8L Engine.

See Figures 1, 2, 3 and 4



Click image to see an enlarged view

Fig. Fig. 1: Location of the CMP sensor shown (water pump removed for clarity)



Click image to see an enlarged view

Fig. Fig. 2: Circuit and connector diagram for CMP Sensor



Click image to see an enlarged view

Fig. Fig. 3: CMP diagnostic chart page 1



Click image to see an enlarged view

Fig. Fig. 4: CMP diagnostic chart page 2

3.4L Engine

Diagnostic Aids-check for:



Incorrect harness routing near secondary ignition components.
 
Ignition coil arcing to the wiring harness or to the Ignition Control Module. Check the ignition coils for cracks, carbon tracking, or other signs of damage.
 
Secondary ignition wire(s) arcing to the wiring harness.
 
Check for a poor connection or damaged harness: Inspect the PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connections and damaged harnesses.
 
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.
 
Perform an intermittent test: If connections and harnesses check OK, monitor a digital voltmeter connected from the PCM terminal "RB9"(cam signal) to ground while moving related connectors and wiring harnesses. If the failure is induced, the voltage reading will change. This may help to isolate the location of the malfunction.
 

If necessary to perform a test on the camshaft sensor, use the diagnostic repair chart and the wire and connector diagram given here for the 3.4L Engine.

See Figures 5, 6 and 7

Click image to see an enlarged view

Fig. Fig. 5: 3.4L Engine Circuit Diagram for CMP and CKP sensors



Click image to see an enlarged view

Fig. Fig. 6: CMP Sensor circuit performance testing-Page One



Click image to see an enlarged view

Fig. Fig. 7: CMP Sensor circuit performance testing-Page Two

Removal & Installation

Although different in appearance, the camshaft sensor, on both the 3.8L and the 3.4L engines, is located on the timing cover behind the water pump near the camshaft sprocket.

See Figure 8

Click image to see an enlarged view

Fig. Fig. 8: 3.4L Engine Cam Sensor location

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the serpentine belt.
  4.  
  5. Remove the water pump pulley, if necessary.
  6.  
  7. Remove the power steering pump assembly, if necessary.
  8.  
  9. Detach the electrical connector.
  10.  
  11. Remove the retaining bolt, and extract the sensor.
  12.  

To install:
  1. Install the sensor and bolt and tighten to 8 ft. lbs. (10Nm).
  2.  
  3. The remainder of the installation is the reverse of the removal procedure.
  4.  

See Figure 9

Click image to see an enlarged view

Fig. Fig. 9: Camshaft and Crankshaft Sensor locations shown-3.8L Engine

 
label.common.footer.alt.autozoneLogo