Coil-on-plug (4-wire)

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

Connection guidance

Connection for diagnostic work will of course 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

  1. Connect PicoScope to the vehicle using breakout leads or back pinning as access dictates.
  2. Run the engine at idle speed.
  3. Minimise the help screen and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  4. Select GO or press the space bar to see live data.

Note: 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 three 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 volts to about 4 volts at coil switch-on and then returns to 0 volts at coil switch-off. The time between these events is the dwell period or coil saturation time, determined by the Electronic 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

There are 18 examples of COP feedback signals in the 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

Technical Information

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-volt active-high pulse from the ECM to the coil.
  3. Feedback - typically a 5-volt 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.

Supply current. This can be measured using a current clamp around the ignition supply wire, either close to the coil or at the fusebox. A pulse should be seen whenever the coil fires. If the supply and trigger voltages are present but there is no supply current pulse, the coil has probably failed open-circuit. If there is a current pulse but no ignition, the coil output or spark plug may be short-circuited.

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 millivolts. 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.

Suitable accessories

  • Premium 6-way breakout lead set


  • Back-pinning Probe Set


  • Flexible Back-pinning Probe


  • Large Dolphin/Gator Clips


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


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


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.

1 comment | Add comment

August 19 2016

i give thanks to pico

Your email address will not be published. Required fields are marked *

Guided test: Trigger and Feedback (4-wire)