Products suited to this guided test*
  • Premium Test Leads: Set of four leads 3 m (TA125 - TA128)

  • *At Pico we are always looking to improve our products. The tool used in this guided test may have been superseded and the product above is our latest version used to diagnose the fault documented in this case study.

Coil-on-plug (4-wire) - trigger and feedback - voltage

The purpose of this test is to examine the individual signals in a 4-wire COP unit to identify the signals and verify correct operation.



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.


How to perform the test

View connection guidance notes.

  1. Use the vehicle wiring diagram to identify the COP circuit functions.
  2. Connect PicoScope Channel A to the coil signal circuit.
  3. Connect PicoScope Channel B to the coil feedback circuit.
  4. Run the engine at idle speed.
  5. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.

  6. Start the scope to see live data.
  7. With your live waveforms on screen stop the scope.
  8. Turn off the engine and ensure the ignition is off.
  9. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.


This test is for a 4-wire COP with a feedback signal to the ECU. Some 4-wire COPs have two ground pins and no feedback signal, these should be tested as a 3-wire COP please see 3-Wire COP Test.

Example waveform

Waveform notes

The Example Waveform is showing the trigger signals from the coil selected on Channel A and the common feedback signal on Channel B.

Channel A. Trigger Signal.

The trigger signal rises from 0 V to about 4 V at coil switch-on and then returns to 0 V at coil switch-off. The time between these events is the dwell period or coil saturation time, determined by the Engine Control Module (ECM) or ignition amplifier.

Channel B. Feedback signal.

The feedback signal tells the ECM that ignition has occurred. The feedback signal on this engine is common to all four cylinders, so there are four feedback pulses for every engine cycle.

Waveform Library

Go to the drop-down menu bar in the lower left corner of the Waveform Library window and select COP feedback signals.

Further guidance

A 4-wire COP has the following connections, pin numbers may vary depending on the type of coil.

  1. Positive supply - switched battery voltage.
  2. Trigger - typically a 5 V active-high pulse from the ECM to the coil.
  3. Feedback - typically a 5 V active-low pulse from the coil to the ECM.
  4. Ground/Earth - battery negative.

In addition to the trigger and feedback signals shown in the waveform above, it is sometimes useful to monitor the positive supply voltage and current and the ground voltage. For instructions on checking the supply and ground/earth pins, see the 3-wire COP test.

Positive supply voltage. This should be close to battery voltage. If it is low or absent then the ignition system is not receiving enough power and the coil will not function.

Ground. A small pulse will be seen on this signal during ignition as the coil draws current from the battery, but the pulse height should not exceed a few hundred mV. A larger voltage indicates too much resistance in the ground wiring, which could cause an ignition fault.


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 (4-wire) - trigger and feedback - voltage