Want to upsell engine decarbs?

Brand new tools and proven techniques help repair or even prevent carbon build up.

Tools Used:

  • J2534 pass-thru device
  • Fuel system cleaning equipment
  • Fuel injector bench tester and ultrasonic cleaner
  • Scan tool
  • Carbon build-up analyzer

Vehicle Application:

2007 Chevy Suburban 5.3L, 2000 GMS Safari 4.3, 2009 VW Jetta, 2000 Toyota Camry 2.2L

Customer Concern:

Low idle, possible P0121 and P0507, P2004 and no performance faults.



Test/procedures for a 2007 Chevy Suburban 5.3 with a P0121:

Summarized diagnostic steps provided from TSB PIP4578, courtesy of Alldata.

1. After a throttle body-related repair, with a scan tool, perform a "reset idle learn/idle learn reset" procedure to erase/reset the learned throttle angle.

2. If the DTC and/or related symptoms do not go away, do a "soft reset" to erase the PCM's memory and update its calibration ID if possible.

3. If the throttle body has been replaced and the module has been updated, and there is still a problem, replace the PCM.


Carbon build-up is an invisible boogeyman in automotive repair. It gradually saps performance, creates pinging and causes low-idle issues.

Many shops have become involved in the profitable field of fuel system cleaning as preventative maintenance. Some shops find this hard to sell because it is hard to prove to a customer that a vehicle needs it. Brand new tools have changed this.

Furthermore, repairing carbon-related issues is serious business as well. Different tools assist the technician in diagnosing component failures, cleaning intakes, flow testing injectors and much more.


Upsell customers on fuel system cleanings

In the old days, customers had to take the technician’s word for it if an engine needed a decarb. This all changed with the invention of the borescope. All the technician has to do is remove a spark plug, put the borescope down the hole and show the customer that there is carbon. With the invention of color borescopes and SD cards, it has become easier than ever to use this technique (See Fig. 1).

However, with the increasing amount of covers, use of coil-on-plug ignition and hard-to-remove spark plugs (such as on Fords), the time needed to use this upsell technique has grown exponentially. At the same time, with the increase of direct fuel injection systems that create an increasing amount of carbon build-up, the need for fuel system cleaning has also increased.

Thanks to new technology, carbon build-up can be detected without taking anything apart on the vehicle. At the cutting edge of carbon build-up detection is the combustion performance tool (CPT) developed by Thompson Automotive Labs, and the AutoEKG, developed by Automotive Test Solutions and exclusively available for lease from ITW Professional Automotive Products.

The tools fundamentally perform the same task, but work a little bit differently. Both tools use a pressure transducer in the exhaust pipe (See Figs. 2A and 2B) that measures irregularities in exhaust pulses in order to detect carbon build-up. The AutoEKG also uses an antenna on top of the engine to assist in its calculations. The computers in these tools then determine how bad the carbon build-up is in a vehicle, using a one to 10 scale.

Tools like these offer shops the ability to upsell vehicles on fuel system cleanings without a lot of investment in time, and they will grow ever more important as vehicles move to higher compression ratios and have less profitable maintenance and serviceable items.


2007 Chevy Suburban 5.3L, low idle and P0121

A lot of GMs with 5.3L motors have throttle bodies going bad from carbon build-up. Usually this results in rough running, hard starts and a P0121 DTC.

The cause is excessive carbon build-up at the throttle plate (Fig. 3, next page), holding the throttle plate slightly open. These electronic throttle bodies, with the proper precautions, can be cleaned properly and have the throttle position relearned, but let it be noted that many dealers simply replace the part. Nonetheless, if the throttle body isn’t cleaned soon enough, the vehicle will not relearn throttle position and the throttle body will need to be replaced, regardless.

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