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.

Connection guidance

Connection for diagnostic work will vary dependent on application.

Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.

General connection advice

PicoScope offers a range of options within the test kits.

Dependent on difficulty of access, choose from:

  1. Breakout leads.
  2. Back-pinning probes.

Testing sensors and actuators (to include relevant circuit/connectors):

  • When testing a sensor, it is desirable to gain access at the control module.
  • When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

  1. Use the vehicle wiring diagram to identify the control actuators switched earth circuits.
  2. Connect PicoScope channel A and channel B to the switched earth circuits.
  3. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  4. Select Go or press the space bar to see live data.
  5. Start and run the engine, increase and decrease engine rpm to observe changes in signal.
  6. With your live waveform on screen select Stop or press the space bar to stop your capture.
  7. Turn off the engine.
  8. Use the Waveform Buffer and Zoom tools to examine your 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.

Example cam timing control valve

Example dual camshaft with two sensors and two actuators

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.

GT156-2

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • Premium 6-way breakout lead set

    £269.00

  • Back-pinning Probe Set

    £40.00

  • Flexible Back-pinning Probe

    £3.00

  • PicoScope Battery Clip

    £2.75

  • Large Dolphin/Gator Clips

    £10.00

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Guided test: Variable camshaft timing - dual control - voltage