Coil-on-plug - primary and secondary voltage (probe)

The purpose of this test is to evaluate the correct operation of the primary and secondary ignition circuits within an externally grounded Coil-On-Plug (COP) style ignition system. The primary and secondary ignition voltages reveal the dwell period, peak firing voltage, burn time, and coil oscillations during engine run conditions. 

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

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

Channel A: Primary ignition voltage

Plug the 20:1 Attenuator into Channel A on the PicoScope and plug a BNC test lead into the attenuator. Fit a large black clip on the black test connector (earth) and connect the clip to the battery negative terminal. Unplug the coil-on-plug unit's connector and join the two halves using a Universal Breakout Lead of the appropriate size, as illustrated in Figure 1. Identify the wire in the breakout lead that carries the coil-on-plug primary connection, and plug it into the coloured connector on the BNC test lead.

Channel B: COP probe

Using the COP Probe cable with ground clip (TA033), connect the end with the ground clip to the scope's Channel B input and the other end to the COP Probe. Connect the ground clip to a reliable ground point on the engine block.

When placing the tip of the probe on the coil, ensure that you use the flat edge. Try to be consistent with the position on the coil: find the best signal on the first coil to be tested and then repeat that on the other coils.

Example waveform

Waveform notes

The waveforms that you will see during this test are discussed in these topics:

  • Channel A: Primary ignition waveform
  • Channel B: Secondary COP ignition waveform


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

  • Connector breakout lead kit A


  • 10:1 Attenuator


  • PicoScope Battery Clip


  • Large Dolphin/Gator Clips


  • Premium Test Lead: BNC to 4 mm, 3 m


  • Premium Test Leads: Set of four leads 3 m (TA125 - TA128)


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: Coil-on-plug - primary and secondary voltage (probe)