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Solve more transmission concerns in-house with these diagnostic tips

Monday, October 1, 2018 - 06:00
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Years ago, while I was working for a particular shop, we used to view Volkswagens like vampires. We would hold our hands up and use our index fingers to make a cross to repel the evil beings and send them down the road to another shop. After a while I attended some training, purchased a very reasonably priced scan tool that works well on VW/Audi products and dove in. Persistence lead me to realize “these are just cars after all!” My point is attitude. Once we decide to get over the fear of the unknown and start working towards a goal we usually attain said goal. Now the shop still works on VW’s and Audi’s to this day. No need to push those cars out the door.

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Transmission diagnostics are no different. I realize that transmission rebuilding is a specialty by itself and many shops do not perform these tasks in-house. However, with the proliferation of computer-controlled transmissions over the last three decades, there is no reason a competent drivability diagnostic technician can’t apply his or her skills to transmission diagnosis. Don’t ship the car to the transmission shop right off the bat. Pull up your boot straps, adjust your attitude and give it a shot. You might be surprised how many transmission issues can be resolved without major transmission overhaul.

Draw a line

The basic theory is to “draw a line” between an electrical issue and a hydraulic/mechanical issue. If the failure ends up being electrical (wiring, a solenoid or a module for example) then the repair can usually be performed in-house. If all of the electrical components test good then a hydraulic/mechanical issue would be the cause of the transmission issue. At this point, your individual shop can decide if the problem will be dealt with in-house, a remanufactured unit will be installed or the vehicle will be sent to a transmission shop for a rebuild.

As with any diagnosis, a basic knowledge of the system and logical procedure should be followed to avoid going down the proverbial rabbit hole. Figure 1 is a rough flowchart that should lead you down the correct path on most applications. The first step is to do a little research on the basics of how the transmission works, paying attention specifically to areas related to the particular transmission complaint. Technical Service Bulletins (TSBs), reflashes, solenoid apply charts and code setting criteria are some of the areas to focus on here. Second, the fluid level should be checked. Feel free to mix up steps 1 and 2. Step 3, if it hasn’t been done already, is to connect a scan tool and gather codes and any other pertinent data. From there, we need to make a decision on where to go next.

Engine issues must be resolved first. If the engine is not operating correctly it needs to be fixed before we can move forward. Remember, engine operation can impact transmission operation; rarely does transmission operation impact the operation of the engine. Once we have covered the initial steps our path will depend on what data we have obtained to this point. Sometimes, our task may be a simple as scoping the operation of a shift solenoid, while other times we may need to be more creative with our testing techniques.

Figure 1 — A basic flowchart to lead you down a logical transmission diagnostic path

Putting the plan into action

Let’s explore a few broken cars to illustrate the process. The first car will be a 2008 Ford Focus. It has already had its transmission rebuilt and an aftermarket remanufactured valve body has been installed to attempt to resolve a MIL illumination and shifting issue. The PCM has stored DTCs; P0751 – SSA Performance or Stuck Off and P0972 – SSA Control Circuit Range/Performance. During the research phase, it is determined that neither of these codes are set by a circuit fault for SSA (Shift Solenoid A). They have been set due to a performance issue with the shift associated with SSA. It can also be noted that there are no engine related DTCs and the engine is operating correctly.

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