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Enhancing the diagnostic checklist

Have a comprehensive overview to most effectively determine the problem and what actions to take.
Tuesday, June 2, 2015 - 07:00
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The seminar I had the opportunity to present at Automechanika Chicago this past April was about diagnosing transmission concerns to determine if the cause of a malfunction is related to an engine management problem, an ABS issue or an actual transmission malfunction.

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Figure 1
Figure 2
Figure 3

In past seminars and articles I provided in detail a basic diagnostic checklist that was developed from years of diagnosing transmission concerns in shops and on ATSG's technical help line. This list was provided in the introduction part of the seminar handout, which begins with "Information." We look first to see if there are any bulletins or articles already covering the subject. The available diagnostic equipment, as well as the ability to use the equipment, is considered if handling the problem over the phone. Understanding the codes received, checking power and grounds, doing a cursory view of the wiring and connectors while looking for cross-connect possibilities are on this list. Checking into the four main critical PCM/TCM inputs (Engine load, Speed Sensors, Gear Shift Position Switches or Sensor and Temperatures) as well as how the signal is generated and delivered to the controlling computer and computer strategies (ABS, torque reduction, failsafe, sport and economy modes, adaptations, manual tap shift controls, start/stop technology or neutral controls, etc.), transmission misapplication, transmission fluid and aftermarket programming, products and parts round out the list. Having this comprehensive overview goes a long way in determining which avenue one needs to take based on the problem at hand to get to the cause as quickly as possible. Of course it doesn't completely eliminate every possible headache, but it sure can eliminate many of them. The point is, you need to have a plan and how to implement that plan.

The seminar also provided a specific diagnostic checklist with which to consider when dealing with converter clutch apply issues (Figure 1). It was presented as follows.

Before and/or after a rebuild, a shudder or vibration is felt and is perceived as a torque converter clutch apply issue. This shudder could occur during the apply, or sustained through a specific driving condition such as medium throttle cruising. Or, the shudder could present itself on coast down. The converter and related items have been replaced yet the condition remains.

Many transmissions on the road today utilize some form of a converter clutch slip control strategy, which in time develops problems resulting in shudder complaints. With converter clutch problems, rings, bushings, solenoids, fluids and valve body bore wear being the usual issues causing shudder complaints, other reasons perceived as a converter clutch shudder can be overlooked or not considered at all.

The following is a list of possible causes to converter clutch concerns, as well as what is not, but is perceived as one. The idea of this list is to provide a wider bandwidth in diagnosing converter clutch issues.

Typical causes of actual converter clutch concerns:

1. The converter itself
2. Moisture/glycol intrusion (Figures 2 and 3)
3. Converter clutch related o-rings, sealing rings and bushings
4. Converter clutch related solenoids and valves
5. Incorrect or stretched out converter attaching bolts
6. Adaptations (Figure 4)
7. Programming

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