Distributorless Ignition System (DIS) 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.

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.


Note: 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.

How to perform the test



Uninsulated HT pickups are designed to clip around double-insulated HT cables only – they are not designed for direct connection to a hazardous live voltage. To prevent injury or death, switch off the engine and secure against restart. Clean and inspect the HT lead for damage to insulation and fit only to undamaged fully insulated leads. Ensure that leads are safely clear of hot and / or rotating parts. The engine can now be restarted for the test duration.


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.

  1. Ensure the ignition is turned off.
  2. Plug a 10:1 attenuator into PicoScope channel A.
  3. Connect Channel A to the primary negative terminal of the coil unit.
  4. Plug a secondary ignition pick up into 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. Plug a low amp current clamp into PicoScope channel C. Select the 20 A scale, switch on and zero the current clamp before connecting around the coil unit primary power supply circuit.
  7. Start the engine and run at idle.
  8. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  9. Start the scope to see live data.
  10. With your live waveforms on screen stop the scope.
  11. Turn off the engine. Ensure the ignition remains off.
  12. Use the Waveform Buffer, Zoom and Measuring 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).


If your current waveform does not appear or looks to be inverted. Stop the test, remove the clamp turn it around and re-fit. Then start and run the test again.

Example waveform

Example DIS coil pack

Further guidance

For further information, see the following topics:

  • Primary voltage
  • DIS secondary voltage
  • Primary current


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


  • Secondary ignition pickup (capacitive with BNC)


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


  • Back-pinning Probe Set


  • Flexible Back-pinning Probe


  • Large Dolphin/Gator Clips


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Guided test: Secondary vs Primary Voltage and Current