Products suited to this guided test*
  • 20 A / 60 A DC (low amps) current clamp

  • Coil On Plug (COP) and Signal Probe

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 The tools used in this guided test may have been superseded and the products above are our latest versions used to diagnose the fault documented in this case study.

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. 



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.

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

Scopes with a 200 V range, such as PicoScope 4x25 models, do not need an attenuator for this test.

All other PicoScope Automotive models need an attenuator on the channel input. You can use either a 10:1 or a 20:1 attenuator provided that you adjust the PicoScope software accordingly. Select from the appropriate Channel Options menu:

  • Probe > x10 for a 10:1 attenuator
  • Probe > x20 for a 20:1 attenuator


How to perform the test

View connection guidance notes.

  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 clamp to PicoScope Channel C, select the 20 A scale and zero the clamp.
  5. Connect the low amp clamp to the coil power supply circuit.
  6. Start the engine and allow it to idle.
  7. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your 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 waveforms on screen stop the scope.
  11. Stop the engine and switch off the ignition.
  12. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.


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.

Example waveform

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.

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