How to connect the oscilloscope when testing:- an AC-excited camshaft sensor
Plug a BNC test lead into channel A on the PicoScope, place a large black crocodile clip on the test lead with the black moulding (negative) and an acupuncture probe onto the test lead with the red moulding (positive). Plug a BNC test lead into channel B on the PicoScope, and place an acupuncture probe onto the test lead with the red moulding (positive).
Place the large black crocodile clip on the battery negative and probe the sensor with the two acupuncture probes.
The sensor has three wires, two carrying the alternating current (AC) waveform illustrated in the example on this page, the other wire an earth.
Fig. 13.1
Figure 13.1 shows the two acupuncture probes back-probing the camshaft sensor multiplug at the connection within the recess of the cam cover on the Vauxhall ECO TEC engine.
Example AC-excited camshaft sensor waveform
Camshaft sensor - AC-excited waveform notes
This type of sensor is used on some of the Vauxhall ECO TEC engines. This Cylinder Identification (CID) sensor differs in operation from the other inductive sensors by having an Alternating Current (AC) voltage supply to the CID sensor. The Electronic Control Module (ECM) supplies a high frequency of 100 to 150 kHz (100,000 to 150,000 cycles per second) to an exciter coil that is located close to a rotating disc.
The disc is located at the end of the camshaft and has a section removed that, when aligned with the sensor, allows the frequency to excite the receptor (through mutual inductance) and returns the signal to the ECM, indicating the position of number 1 cylinder.
As the frequency is so fast, the time scale should be set to 20us/division so that the oscilloscope can capture the frequency.
The CID sensor is used as a reference by the ECM to determine the camshaft's position, from which the correct timing for the sequential fuel injection can be determined.
Technical information - camshaft sensor
This camshaft sensor differs in operation from the other sensors by having an Alternating Current (AC) voltage supply. The ECM supplies a high frequency of around 100 to 150 kHz to an exciter coil that is located close to a rotating disc.
The disc is located at the end of the camshaft and has a section removed that, when aligned with the sensor, allows the frequency to excite the receptor (through mutual inductance). The signal returns to the ECM, indicating the position of number 1 cylinder.
