AECS Technics
January 26, 2020 / 0 Comments / AECS Technics

AECS Technics – Sticky Throttle

In our latest technical article, Herbert shares on a method of diagnostics that is truly innovative in the story of the Sticky Throttle.  Included is our latest news and training dates.  We hope you will enjoy the read.

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sticky throttle - AECS technics

In this article, we look at a combination of common faults rather than reviewing a single issue that we typically deal with, within our technical support. It is my hope this will make your day to day as a technician easier.

Various diagnosed faulty H-bridge controlled valves, as used in AECS training seminars.

We often get presented with diagnostic cases where a throttle butterfly (drive by wire) or EGR valve gets sticky as a result of carbon build-up or bearing wear.  On some vehicles, the valves are so bad that it will result in a fault code.

Within our Technical Support, we have developed this beautiful way of determining with the utmost accuracy if the valve is the cause of an engine surge, fault code or merely the result.  I think you will find this method of diagnostics truly innovative; it also gives you an insight into what we are doing here to advance the automotive industry in NZ.

You first need to understand that for example, a throttle valve (and most EGR valves) are a DC motor with 2 wires. Both wires of the DC motor are connected to the ECU and are controlled by the ECU.

Sample wiring diagram throttle body


The ECU can pulse one wire to earth or the other, while the opposing wire is connected to 12V.  This is called H-bridge duty cycle control.  This is also explained in our training videos on H-bridge control and included diagnostics.




In simple terms let’s look at a ‘raw’ scope recording of the 2 wires to the throttle body DC motor.

10 second recording with the 4 Channel 1GHz ATS WiFi6004XM scope

The recorded pattern by itself means very little, even when you zoom in it means not a lot:

10-second recording with the 4 Channel – Zoomed in

How do you see if this throttle is the cause of the engine surging?

The ATS Scope has a unique function where analysis is possible in great detail and with the utmost precision on a recording.

Let’s explain
Each of the two wires is duty cycle controlled.  A simple function of the scope is to convert both lines into a duty cycle line:

ATS scope recording (2 channels with 2 duty cycle math channels added)

That does not make things a lot clearer. I certainly cannot see if this throttle body is behaving correctly or is the cause of a surge.  Let’s see if combining the 2 duty cycle channels is going to reveal anything useful:

ATS scope recording (2 channels with 3 math channels added)

The combination channel is what we are after. The combination math line shows us the effort the ECU is putting on the throttle DC motor to try to torque it to whatever position it wants.

Let’s remove the actual duty cycle lines and leave only the combination line, add the TPS (throttle positions sensor) and APS (accelerator pedal sensor) signals:

Still the same recording with the ATS WiFi 6004XM 4 channel scope

There is still no 100% answer to say that this signal is good or bad!  Whilst understanding the signals let’s see if we can pick out the difference with a recording on a surging engine without a fault code.

Recording on a similar vehicle with a sticky throttle body (worn bearings). At A the throttle gets opened a little, at B it gets opened even further.

It is really clear to see that the combined duty cycle line is moving much more! On the good car, the combined duty cycle line is not as high versus the prolonged high as in the recording of the surging car.

You can see in area A and B that the ECU needs to do great effort before the throttle actually moves. Towards the end of this last recording, you can actually see the same during the closing of the throttle.  The effort to move the throttle should only be moderate duty cycle changes, not a large effort for the throttle to then ‘pop’ to the new position.

It has never been easier to diagnose complex electromechanical faults with the unique capability of this wireless ATS scope.  Making things easy in our ever-complex world is what is needed. To have ‘just a scope’ is not sufficient in reality.

Yes most (toy) scopes out there can show the pulses as in picture2, some can even record as in picture1, but that is where it all stops.  Investing is such a scope does not bring you any closer to a conclusion in diagnostics. We are confronted with good technicians buying the wrong gear every day. Technicians who have been largely incorrectly disappointed in themselves, as it can be the (very often expensive) toy scope they used for the job!

In my experience, it is hardly ever the ability of the technician which is the shortcoming! The level of people in the industry is predominantly very good.  I wish I could tell everyone to make sure they purchase diagnostic equipment with care and thought, just to enable and motivate the technicians who need to do the work.

Technical back up, training and diagnostic equipment are what we focus on with our whole team at AECS. I hope that it helps you to know that we are here for you!

Herbert Leijen

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