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Today's transmission malfunctions

A conversation was pretty revealing as to the concerns today's transmission shops face in repairing vehicles.
Monday, July 28, 2014 - 07:00
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A conversation was pretty revealing as to the concerns today's transmission shops face in repairing vehicles.

The past couple of months the main article in POWERTRAIN PRO has looked at the DSG transmission with quite a bit of focus placed on programming. Vocabulary like data, variables, mapping and algorithms might be heard these days when speaking about programming. Who would have ever thought these terminologies would be a part of conversation related to the world of automotive repair?

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But so it has become. Recently, I had a conversation with Bernie Thompson from Automotive Test Solutions were we had a discussion of what it would take to write a program to make just one up-shift. Immediately, engine load and vehicle speed variables became the dominating data towards the making of a shift. But as you really dig in, there are so many other factors in play. Not only do you need to write language that will determine at what speed a shift will take place under various engine loads, shift feel also needs to be considered. Factors like temperature, adaptations, ABS and engine management (torque reduction) also are brought into the equation.

Then there is skip shift technology, power and economy modes as well as manual shift mode and failsafe strategies to add into the programming. Not to mention how software works hand in hand with the architectural design of the transmission. A shift strategy might be written differently with a clutch pack that has a wave plate and counter balance piston as opposed to one that does not have either or.

All of these various aspects mentioned and others need to be considered when writing a program to shift the transmission while keeping in mind fuel economy and emission control. By just this brief overview alone, you can begin to imagine the amount of mapped data it takes for just one up-shift is incredible. Now consider transmissions with 6, 8, or 10 speeds. What a massive programming task engineers have to make it all work.  It is a respectful task to say the least, and one that is accomplished amazingly well. But, do you think it’s possible that something could be overlooked, or a variable missed in the writing of the program every now and again?

Apparently so given the many reprogramming fixes we see for a wide variety of reasons. Shift scheduling, shift feel, garage shifts, code setting, shudders, TCC operation, system response times are some of the issues being corrected by reprogramming. As a result, checking to see what reprogramming fixes are available has become a primary step in many shops diagnostic routine. Those who have yet to include this necessary diagnostic step might find themselves spending time and money wastefully chasing a problem caused by a computer software malfunction.

But to put a little different spin on this line of thinking, the main part of the conversation Bernie and I had was to think through all the possible variables involved for the computer to make a specific command. This line of thinking can become helpful diagnosing problems that are not caused by errors in software. Simply put, to have an understanding of all the various aspects of the vehicle in how they interact with one another. What variables are the engineers including in an operation and are those variable being controlled properly or not. If a transmission is exhibiting late shifts, no doubt most will consider looking at engine load parameters while other will also look at tire size and their inflation pressure. If all possible variables are being controlled properly, yet the computer is not providing the proper command, software issues should then be considered.

If all the main inputs are correct to the microprocessor, yet the shift solenoid commands are not controlling the transmission shift points correctly, there are several possibilities. The Powers and ground to the Transmission Control Unit (TCM) could have resistance thus dropping the current supply to the microprocessor; this in turn can cause many different problems such as shift scheduling errors. Additionally other control units that share data on a bus can have a direct affect on the shift scheduling. This could be something as simple as a 4 wheel drive indicator showing that 4 wheel drive is engaged when it is not.  Software issues in the TCM or other control units that share data to the TCM could cause shift scheduling errors as well.

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