The coil-on-plug probe investigates

18 December 2014  

By Steve Smith

As we all know, an hour is never long enough, but it does provide you with an opportunity to present your customer with an overview of their vehicle and evidence to either warrant additional diagnosis time or component replacement. The ball is then firmly in the customer’s court.

We all have our own test procedures fine-tuned to various symptoms we come across day-to-day. How we approach various faults is a matter of choice and of course, product knowledge/ease of access etc.

The benefits of a non-intrusive test is to provide an indication of events taking place without disturbing the signals, enabling the technician to plot a course through the engine management to a point where he/she can concentrate their valuable resources and time. Exhaust gas pulsations, relative compression and intake manifold pressure tests spring to mind, to mention just a few non-intrusive techniques.

How does the COP probe actually work and could it be applied in other areas to evaluate additional components?

Figure 1

To answer the second question, “Could it be applied in other areas to evaluate additional components?” The short answer is yes. Knowing how the COP probe can detect the presence of an electrical field about a consumer such as an actuator or solenoid, we can apply the same technique to items such as injectors, solenoids and control valves.

Figure 2

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From all the above it would appear we should rename the COP probe a ‘Signal Probe’ or ‘Sniffer Probe’ as we apply this measurement tool to numerous components other than Coil-on-Plug units.

Using the COP probe in these applications will require the technician to implement other features of the scope such as scaling, to allow the signal to be seen, and filtering to remove noise. Without these additional techniques, the signal will be there but hidden from view as a result of the noise that is characteristic in an engine bay environment.

The fact we can introduce the COP probe into an environment such as an engine bay with both high frequency signals and high voltages present, yet extract a valid signal smaller than 4 mV, is testament to the scope, software and supporting accessories.

A cautionary word of warning when measuring component signals in this fashion. I have chosen to use words such as confirm activity and confirm events rather than test and measure. Please do not assume a component is in perfect working order using the COP probe alone. There is no substitute for best practice; direct voltage and current measurements remain the correct way to evaluate consumers such as those mentioned in this article.

Figure 1: A secondary ignition event