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

The purpose of this test is to investigate the operation of the primary and secondary ignition circuits within an externally grounded Coil-On-Plug (COP) type ignition system. 

Connection guidance

Connection for diagnostic work will vary dependent on application.

Technicians should wherever 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.

To avoid damage to your scope, you may need to use an attenuator for this test.

These instructions do not refer to an attenuator as it is based on our PicoScope 4425 automotive scope.

If you are using a previous PicoScope Automotive model, you will need either a 10:1 or 20:1 attenuator and will need to adjust the Probe settings for the relevant channel.

These settings can be found under Channel Options, then:
• Probe > 10:1 Attenuator
• Probe > 20:1 Attenuator

How to perform the test


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. Use manufacturer data to identify the coil circuit functions.
  2. Connect PicoScope channel A to the coil switched earth circuit.
  3. Connect the COP probe to PicoScope channel B and to engine earth.
  4. Connect the low amp current clamp to PicoScope channel C, select the 20 A scale and zero the clamp before connecting to the vehicle.
  5. Connect the low amp current clamp to the coil power supply circuit.
  6. Start the engine and allow it to idle.
  7. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  8. Start the scope to see live data.
  9. Place the COP probe squarely onto the top of the COP unit to be tested, this will now pick up the secondary pattern.
  10. With your live waveforms on screen stop the scope.
  11. Stop the engine and switch off the ignition.
  12. Use the Waveform BufferZoom and Measuring tools to examine your waveforms.

 Note; 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.

Waveform notes

This test produces the three waveforms shown above. Similar waveforms are discussed in the following topics:

  • Channel A (middle, blue): Primary voltage
  • Channel B (bottom, red): Secondary voltage with COP probe
  • Channel C (top, green): Primary current

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, COP (Coil on plug ignition) secondary voltage.


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

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


  • Coil On Plug (COP) and Signal Probe


  • Premium 6-way breakout lead set


  • Back-pinning Probe Set


  • Flexible Back-pinning Probe


  • Large Dolphin/Gator Clips


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Guided test: Coil-on-plug - primary and secondary voltage (probe) with current