Products suited to this guided test*
  • Secondary ignition pickup (capacitive with BNC)

  • 20 A / 60 A DC (low amps) current clamp

  • *At Pico we are always looking to improve our products. The tools used in this guided test may have been superseded and the products above are our latest versions used to diagnose the fault documented in this case study.

Distributorless Ignition: secondary vs primary voltage and current

The purpose of this test is to examine and compare the primary current and voltage vs the secondary voltage within a DIS unit.



This test involves measuring a potentially hazardous voltage.

Please ensure you follow manufacturers' safety instructions and working practices and ensure the rated voltage for all accessories you are using meets or exceeds the expected voltage.





Uninsulated HT pickups are designed to clip around double-insulated HT leads only – they are not designed for direct connection to a hazardous live voltage.

To prevent injury or death, when connecting or disconnecting an HT pickup:

  1. switch off the ignition
  2. clean the HT leads
  3. inspect them for damage
  4. clip the HT pickup over the desired undamaged HT lead
  5. ensure all test leads are kept clear of hot or rotating parts before starting the engine


How to perform the test

View connection guidance notes.

  1. Ensure the ignition is turned off.
  2. Connect a 10:1 attenuator to PicoScope Channel A.
  3. Connect Channel A to the primary negative terminal of the coil unit.
  4. Connect a secondary ignition pick up to PicoScope Channel B.
  5. Connect the secondary ignition pick up around one of the coil HT leads and ensure the pick up has a good earth.
  6. Connect a low amp clamp to PicoScope Channel C.
  7. Select the 20 A scale and zero the clamp.
  8. Connect the clamp around the coil unit primary power supply circuit.
  9. Start the engine and run at idle.
  10. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
  11. Start the scope to see live data.
  12. With your waveforms on screen stop the scope.
  13. Turn off the engine. Ensure the ignition remains off.
  14. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.


If the secondary voltage waveform appears inverted then this is because the output is positive-fired. Move the secondary ignition pick up onto a different HT lead.

Alternatively, you can change the settings to look at a positive-fired coil by selecting the settings for channel B and changing the probe from Secondary Ignition Probe (Inverted) to Secondary Ignition Probe (Pos).


The orientation of the current clamp relative to the wire will determine whether it has a positive or negative output. If a live waveform does not appear on your screen, or appears to be inverted, try reversing the orientation of the clamp.


This helpfile refers to a 10:1 attenuator. If you are using a 20:1 attenuator please adjust the Probe settings for the relevant channel. These settings can be found under the Channel Options button, then: Probe > 20:1 Attenuator.

Example waveform

Waveform notes

These known good waveforms have the following characteristics:

  • They are representative of standard primary voltage and current and secondary voltage waveforms.

Further guidance


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.

Help us improve our tests

We know that our PicoScope users are clever and creative and we’d love to receive your ideas for improvement on this test. Click the Add comment button to leave your feedback.

Add comment

Your email address will not be published. Required fields are marked *

Guided test: Secondary vs Primary Voltage and Current