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

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Scan Tool Tech

While systems can and will differ, here’s a look at common ADAS features, their general configurations and calibration requirements.

scan tool tech

Advanced Driver Assistance Systems (ADAS) require the use of a scan tool for diagnostics, and the majority of the time, it’s required for post-repair calibration. ADAS, like any other system, requires a diagnostic routine, which begins with a base knowledge of the system. Knowing ADAS will help understand fault symptoms and scan tool data for the most efficient diagnosis.While systems can and will differ, here’s a look at common ADAS features, their general configurations and calibration requirements.Parking assist sensors, of which there can be more than one, are generally located in the front and rear bumpers. They are the inputs that affect active parking assist and parking collision warnings. Any time they are disturbed in any manner, a static calibration must be performed with a scan tool.Side object sensors, sometimes called collision avoidance sensors, are commonly located in the rear bumper. These sensors provide input for blind spot warnings, lane change alerts and rear cross traffic warnings. Static calibration with a scan tool is required when these are removed or replaced.Rear vision cameras will be located in the rear decklid, liftgate or tailgate, and act as either a backup camera alone, or part of a surround view system if the vehicle is so equipped. These cameras generally require a dynamic calibration, and no scan tool is required.A forward-looking camera is sometimes located behind the grille, and usually part of a surround view system. These too do not require a scan tool, but a dynamic calibration must be performed when they are removed or replaced.Different ADAS features may have dedicated control modules which can be located in various areas, often behind interior panels. As with most control modules, these require scan tool programming when replaced and, depending on the system, both static and dynamic calibrations may be required.The Haptic Seat Motor creates the vibration to provide a safety alert for blind spot, forward collision, lane departure, lane keep assist, parking collision and rear cross traffic warnings. These motors, sometimes called seat warning actuators, generally require no type of calibration.Cameras located in a sideview mirror are part of surround view systems. These require calibration when removed or replaced, but most of them dynamic, and no scan tool is required.The steering angle sensor located in the steering column is an input for lane keep assistance, and a static calibration is required with a scan tool any time it is removed or replaced, or any time a wheel alignment is performed.Last, but not least, is the front view, or forward-looking camera located in the windshield area. This camera is a vital part of adaptive cruise control, automatic emergency braking, automatic high beam headlights, forward collision and lane departure warnings, and lane keeping assistance. A scan tool and static and dynamic calibration are required after removal and replacement, but also after windshield removal or replacement, or any service that affects the ride height of the vehicle. TS

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