Variable camshaft timing - dual control - voltage

The purpose of this test is to compare the duty cycle signal of the VVTi control actuators against manufacturers specifications.

How to perform the test

View connection guidance notes.

1. Use manufacturer data to identify the control actuators switched earth circuits.
2. Connect PicoScope Channel A. to the inlet camshaft actuator switched earth circuit.
3. Connect PicoScope Channel B. to the exhaust camshaft actuator switched earth circuit.
4. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
5. Start the scope to see live data.
6. Start and run the engine, increase and decrease engine rpm for around 10 s.
7. With your waveforms on screen stop the scope.
8. Turn off the engine.
9. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Note

The solenoid has two terminals, both may have supply voltage at ignition on.

The switching frequency is dependent on engine system variations at the time of testing, EGR function, temperature, RPM etc. The switching frequency and duration will also vary with different vehicle manufacturers.

Example waveform

Waveform notes

The Variable Camshaft Timing (VCT) solenoid is an actuator. It is commonly supplied with an ignition live and a ground provided by the ECM. Note that either the positive or the ground duty cycle can change depending on the design of the system by the OEM.

You can compare the duty cycles of both actuators with each other and against manufacturer's information, but you may need to load the engine to make the duty cycle of the exhaust actuator change with engine operating parameters and EGR conditions.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, Variable Camshaft Timing VCT solenoid voltage.

Further guidance

The use of VCT has become widespread throughout the automotive industry as the technology becomes cheaper and more manufacturers take advantage of it.

Variable camshaft timing is used to increase engine torque in the low engine speed range and to increase power in the high engine speed range. The use of VCT means that we can control the closing and opening times of inlet and exhaust valves. As a result VCT may also be used in place of an EGR (exhaust gas recirculation) valve.

Should you suspect a fault with the signal, test the wiring from the Powertrain Control Module (PCM) to the VCT actuator.

Ensure that the PCM has good power supplies and grounds where required or specified.

GT156