PCM must see signals from both sensors to start.
Automatic Shutdown (ASD) and Fuel Pump Relays
The Automatic Shutdown (ASD) and fuel pump relays are located in the Power Distribution Center (PDC).
The camshaft position sensor and crankshaft position sensor signals are sent to the PCM.
If the PCM does not receive both signals within approximately one second of engine cranking, it deactivates the ASD relay and fuel pump relay. When these relays are deactivated, power is shut off to the fuel injectors, ignition coil, oxygen sensor heating element and fuel pump.
Cam Position Sensor-Description and Operation
PURPOSE
Sensor provides PCM with cylinder identification.
PCM uses sensor input to determine fuel injection sequence and ignition timing.
OPERATION
The sensor generates pulses as groups of notches on the camshaft sprocket pass underneath it.
The PCM keeps track of crankshaft rotation and identifies each cylinder by the pulses generated by the notches on the camshaft sprocket.
Four crankshaft pulses follow each group of camshaft pulses.
When the PCM receives 2 cam pulses followed by the long flat spot on the camshaft sprocket, it knows that the crankshaft timing marks for cylinder 1 are next (on driveplate). When the PCM receives one camshaft pulse after the long flat spot on the sprocket, cylinder number 2 crankshaft timing marks are next. After 3 camshaft pulses, the PCM knows cylinder 4 crankshaft timing marks follow. One camshaft pulse after the 3 pulses indicates cylinder 5. The 2 camshaft pulses after cylinder 5 signals cylinder 6. The PCM can synchronize on cylinders 1 or 4.
When metal aligns with the sensor, voltage goes low (less than 0.3 volts). When a notch aligns with the sensor, voltage switches high (5.0 volts). As a group of notches pass under the sensor, the voltage switches from low (metal) to high (notch) then back to low. The number of notches determine the amount of pulses. If available, an oscilloscope can display the square wave patterns of each timing event.
Top Dead Center (TDC) does not occur when notches on the camshaft sprocket pass below the cylinder. TDC occurs after the camshaft pulse (or pulses) and after the 4 crankshaft pulses associated with the particular cylinder. The arrows and cylinder call outs on Figure 4 represent which cylinder the flat spot and notches identify, they do not indicate TDC position.
The camshaft position sensor is mounted in the front of the timing case cover.
CIRCUIT OPERATION
Circuit K7 supplies 8 volts from the Powertrain Control Module (PCM) to the camshaft position sensor. The K7 circuit originates at cavity 44 of the PCM connector.
Circuit K44 from the sensor provides an input signal to the PCM. The K44 circuit connects to cavity 33 of the PCM.
The PCM provides ground for the camshaft position sensor signal (circuit K44) through circuit K4. Circuit K4 connects to cavity 43 of the PCM.
Helpful Information
Circuit K7 also splices to supply 8 volts to the crankshaft position sensor and vehicle speed sensor.
Circuit K4 also splices to supply ground for the signals from the following:
Upstream heated oxygen sensor
Downstream heated oxygen sensor
Crankshaft position sensor
Throttle position sensor
Manifold absolute pressure sensor
Engine coolant temperature sensor
Knock sensor
Intake air temperature sensor
Vehicle speed sensor
NOTE: The distance between the sensor and camshaft sprocket is critical to system operation. Be sure paper spacer is attached to sensor face when installing sensor.
Service Bulletin-Cam/Crank Sensor - No Start Diagnostics
NO: 18-24-97
GROUP: Vehicle Performance
DATE: Aug. 8, 1997
SUBJECT:
No Start Diagnostics Cam/Crank Sensor
MODELS:
1997 (FJ) Avenger/Sebring/Talon
1997 (GS) Chrysler Voyager (International Market)
1997 (JA) Breeze/Cirrus/Stratus
1997 (JX) Sebring Convertible
1997 (LH) Concorde/Intrepid/Vision/LHS/New Yorker
1997 (NS) Town & Country/Caravan/Voyager
1997 (PL) Neon
NOTE: THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A 2.0L DOHC/SOHC (NATURALLY ASPIRATED), 2.4L, 3.3L, 3.5L, OR 3.8L ENGINE.
DISCUSSION:
If a vehicle exhibits a no-start due to failure of the cam or crank sensor, the opposite sensor may be reported as the DTC (i.e. bad cam sensor sets crank sensor DTC and vice versa). The faulty sensor may generate a signal strong enough (at key "ON") to be interpreted by the controller as a legitimate signal. Since the engine is not running, the opposite sensor will not be generating any pulses. The controller, expecting corresponding pulses from both sensors, matures a fault for the sensor that is not generating any pulses. In this case, the good sensor is reported as faulty.
To verify which sensor is at fault, use the DRB III and select DRB III Standalone, 1994 - 1998 Diagnostics, select Engine system, select Monitor Display, and No Start monitor. Under the No Start monitor the cam and crank sensors should display a no response or LOST on the display. If a sensor is reporting a signal at key ON", it should be replaced.
POLICY: Information Only