Transmission Diagnostics

Transmission Diagnostics

A full-function scan tool is the most valuable tool you can have, especially when it comes to transmission diagnostics.

Are new cars harder to work on than old? It depends on who you talk to. And if old cars are deemed easier, what takes the blame for the difficulty on the new versions? You can be certain that it’s computers and electronics.

Someday we’ll all be gone, but until then there’s a group of us that remembers the technology of the ’60s and ’70s, and in our minds, those cars were comparatively simple. With the basic tools we had in our box, we could diagnose and fix any aspect of any year, make or model – that is, until it came to the automatic transmission.

Automatic transmission diagnostics have always been the Achilles heel of many a technician, and, in many cases, even with some of the best technicians I have known, this was the one and only repair that got shipped off to someone who specialized in it. Outside of fluid changes, level and condition, the extent of repairs covered vacuum modulators, the throttle pressure (kickdown) cable, the mechanical linkage or cable from the shifter and maybe the output shaft seal. Aside from that, it was the glutton for punishment who decided to delve into the great mystery inside.

Some things haven’t changed, and the automatic transmission still holds a strong place in the market with specialty shops, but today’s technician is far more empowered to work on them. The same thing that is often blamed as making cars more difficult makes the automatic transmission easier to understand: computers and electronics.

A full-function scan tool is the most valuable tool you can have and there is no exception when it comes to transmission diagnostics. We are used to the engine control module (ECM) telling us there is a problem and storing a trouble code, usually long before we notice anything wrong with the way it runs. Transmissions are the same way. Their control and operation are so precise, that the transmission control module (TCM) will recognize any deviation in performance and store a trouble code, and most likely the driver didn’t so much as notice a hiccup.

A full-function scan tool is the most valuable tool you can have and there is no exception when it comes to transmission diagnostics.

Checking the fluid level and condition is always the first step in transmission diagnostics, and to the best of my knowledge, analyzing fluid condition is the one thing a scan tool can’t do…at least not yet. But, no ifs, ands or buts, this is always the first step. Low or contaminated fluid can cause many problems, which can result in a transmission DTC, so go no further until you know you’ve got good fluid.

Assuming the fluid is good, your scan tool is next. If there is a transmission DTC, the troubleshooting flow chart will take you step-by-step through diagnosis of the problem, utilizing scan tool data. In the past, you were blind without transmission knowledge and a myriad of pressure gauges and connections to hook up, and in reality, you didn’t even know where to start.

With scan tool data and flow charts, not only do you know where to start, but it will help you learn transmission functions by correlating symptoms to the eventual causes. Many automatic transmissions also require relearn procedures depending on the type of repair that was performed, and your scan tool is necessary to perform these procedures. So, follow your scan tool, let it be your teacher and add automatic transmission diagnosis to your repertoire. TS

You May Also Like

Not a Pry Bar or Punch: Welcome to the Funnel

Just when you thought you knew almost every part of a car, you learn something new.

Just a few days ago, a friend called me to ask an automotive-related question. We are good friends, but I’m not his “regular” mechanic. He wishes so, but I don’t do much on the side, primarily because I’d have no time for anything else in my life. He respects that, but also knows that I’m always willing to help out in a pinch, and his regular mechanic wasn’t feeling well and wouldn’t be available for a few days.

Electrical Circuit Diagnostics

Your diagnostic approach needs to be well thought out, and it starts with your equipment.

Streamlining the Diagnostic Process

Why is it that one technician can take 20 minutes to diagnose a car and another may take a week?

Automotive Ignition System Strategy

When there’s a misfire DTC, it’s likely related to the ignition system. Grab your scan tool for your next steps.

Diagnosing Faults on Modern Cars and Trucks

A scope can be used to give the technician an in-depth understanding of the operation of a complicated system.

Other Posts

Not a Pry Bar or Punch: Does it Really Have to be That Hard?

Should brake light bulbs really be that involved to replace? Lights are a safety item that should be easy for anyone to do.

Snap-on Adds ZEUS+ Training Modules to Website

The training helps technicians navigate the features and functionality of the new platform.

Smash the Peppermint Pig

What’s the best tool an auto technician can own? Is it really possible to say?

2022 TechShop Year in Review

Just in case you missed any of our great feature articles this year, we have pulled them together in one spot for you!

Clean auto shop