1997 Nissan SENTRA
Submodel: GLE | Engine Type: L4 | Liters: 1.6
Fuel Delivery: FI | Fuel: GAS
Camshaft Position (CMP) Sensor Testing
CAMSHAFT POSITION (CMP) SENSOR
Pick-up Coil CMP
Description
The Camshaft Position (CMP) sensor consists of a permanent magnet, yoke and coil. The CMP sensor is positioned next to the cam gear. As each cam gear tooth passes the sensor
magnetic pick-up an AC voltage pulse is induced in the coil. The PCM counts the number of pulses to determine the camshaft speed. The number of pulses counted in one second is the
signal frequency.
The Powertrain Control Module (PCM) uses the camshaft position sensor to manage sequential fuel injection and as part of misfire diagnosis. The PCM constantly monitors the number of
pulses on the signal circuit. The PCM compares the number of camshaft sensor reference pulses and the number of crankshaft position sensor reference pulses received. If the PCM
receives an incorrect number of pulses, Diagnostic Trouble Codes (DTCs) should be stored in the PCM. Some PCM systems will then default to multi-port or "gang-fire" injector operation.
The camshaft position sensor signal is required to sequence the injector operation to the proper cylinder timing. If the camshaft position sensor or circuit is faulty, most engines will start.
However, the PCM misfire diagnostic will likely be affected.
Typical CMP sensor
Testing
1.
Connect a scan tool to the data link connector (DLC) and check the CMP sensor datastream for a normal waveform.
2.
If the scan tool waveform for the CMP sensor is not within the specified values, perform a visual inspection on the CMP sensor, wiring harness, connector and related components
as follows:
Ensure that the connector tabs are fully locked
Check for corroded terminals
Bent pins
Pins pulled back in the connector
Terminal cavities spread open
Harness damage
Sensor damage
Mounting
3.
If the connectors, wiring harness and related mechanical components pass inspection, perform the following procedures to test the CMP sensor, wiring and related modules:
Two Wire CMP
A.
Disconnect the CMP sensor connector.
B.
Check the CMP sensor reference circuit from the PCM or ignition module by performing a circuit resistance test between the CMP sensor and PCM or ignition module. Use the
Component Pin Data for circuit details.
C.
Check the PCM signal circuit to the MAF sensor by performing a circuit resistance test between the MAF sensor and the PCM. Use the Component Pin Data for circuit details.
D.
Repair/replace defective parts as needed and recheck the scan data.
Three Wire CMP
A.
Disconnect the CMP sensor connector.
B.
Check the CMP 12V supply circuit by performing a circuit resistance test between the CMP sensor and the 12V supply. Use the Component Pin Data for circuit details.
C.
Check the MAF sensor signal circuit between the MAF sensor and PCM by performing a circuit resistance test. Use the Component Pin Data for circuit details.
D.
Check the MAF sensor ground circuit between the MAF sensor and PCM by performing a circuit resistance test. Use the Component Pin Data for circuit details.
E.
Repair/replace defective parts as needed and recheck the scan data.
Hall-effect CMP
Description
A hall-effect CMP produces a square waveform that varies in frequency when the magnetic field is interrupted by a shutter wheel blade. The signal switches high as the shutter blade
passes between the hall element and permanent magnet this interruption changes the magnetic field from strong to weak. The hall element contains a logic gate that converts the analog
signal into a digital signal that triggers transistor switching. The transistor transmits a digital square waveform at a variable frequency to the PCM. The hall-effect CMP uses three circuits to
operate it, a power input from the ignition or PCM, a signal output and a ground. The action of the shutter blade interrupting the magnetic field and opens and closes a switch to ground on the
input signal.
Testing
1.
Connect a scan tool to the data link connector (DLC) and check the CMP sensor datastream for a normal waveform.
2.
If the scan tool waveform for the CMP sensor is not within the specified values perform a visual inspection on the CMP sensor, wiring harness, connector and related components
as follows:
Ensure that the connector tabs are fully locked
Check for corroded terminals
Bent pins
Pins pulled back in the connector
Terminal cavities spread open
Harness damage
Sensor damage
Mounting
3.
If the connectors, wiring harness and related mechanical components pass inspection, perform the following procedures to test the CMP sensor, wiring and related modules:
A.
Disconnect the CMP sensor connector.
B.
Check the CMP power input circuit by performing a circuit resistance test between the CMP sensor and the power input. Use the Component Pin Data for circuit
details.
C.
Check the MAF sensor signal circuit to the PCM by performing a circuit resistance test between the MAF sensor and the PCM. Use the Component Pin Data for
circuit details.
D.
Check the MAF sensor ground circuit between the MAF sensor and PCM by performing a circuit resistance test. Use the Component Pin Data for circuit details.
E.
Repair/replace defective parts as needed and recheck the scan data.
Optical CMP
Description
The optical sensor operation is similar to the hall-effect sensor except that it uses a light-emitting diode (LED) and a phototransistor instead of a magnetic field to produce a digital signal. The
signal voltage switches on and off as the shutter passes between the phototransistor and LED to toggle the ground circuit. When the shutter allows light to shine on the phototransistor, the
base of the transistor switches, causing the signal voltage to change state. When light is blocked from the phototransistor, the base of the transistor switches again, and the signal voltage
changes. The optical waveforms are similar to the hall-effect waveforms.
Testing
A.
Disconnect the CMP sensor connector.
B.
Check the CMP power input circuit by performing a circuit resistance test between the CMP sensor and the power input. Use the Component Pin Data for circuit details.
C.
Check the MAF sensor signal circuit to the PCM by performing a circuit resistance test between the MAF sensor and the PCM. Use the Component Pin Data for circuit details.
D.
Check the MAF sensor ground circuit between the MAF sensor and PCM by performing a circuit resistance test. Use the Component Pin Data for circuit details.
E.
Repair/replace defective parts as needed and recheck the scan data.