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

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 while the current flow confirms the integrity of the ignition primary circuit.

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 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 onto the black test connector (earth) and a back-pinning probe on the coloured connector (positive). Place the black clip on the battery negative terminal and probe the coil's negative (or number 1) terminal with the back-pinning probe.

Channel B: Secondary voltage with 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.

Channel C: Primary current

Connect the low-amp current clamp to Channel C of the PicoScope. Select the 20 A rangeif applicable and switch the current clamp on. Rremember to zero the clamp before connecting it to the circuit.

The current clamp should be placed directly onto the coil's supply cable and not around the loom that also contains the negative (or negatives depending on the ignition system). The connection is illustrated in Figure 1.

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


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

  • 30 A (low amps) current clamp


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


  • BNC to BNC Cable with Earth Clamp


  • Coil On Plug (COP) and Signal Probe


  • 10:1 Attenuator


  • Back-pinning Probe Set


  • Flexible Back-pinning Probe


  • 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)


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