When a 2008 Ford Taurus arrived at the transmission shop on a flatbed from the local Ford dealership, it was clear that the 263-horsepower 3.5-liter Duratec had done some damage down the driveline, specifically by the unplanned disassembly of the gearbox’s internals.

With the current transmission thoroughly smoked, and an additional 10 labor hours needed to overhaul it versus an 8-hour quote for removing and installing a remanufactured unit, the shop supervisor informed the customer that the better option was to go with the remanufactured unit.

And this is where the fun began.

Once the customer gave approval, the process of separating the front-wheel-drive transmission from the engine began. As most technicians know, working on a V6 in a front-wheel-drive layout rarely makes for an enjoyable day. This one was quoted at 8 hours for removal and replacement. After wrapping up the job and reprogramming, a quick test drive was deemed necessary before clocking out. In this time, several unpleasant surprises surfaced: erratic shifting, traction control cutting in during the 1-2 shift and going into limp mode, and an overall inability to accelerate effectively beyond 40 mph.

Back at the shop, a long and thorough “hydration” session kicked off, with plenty of questions tossed around. Was a traction control sensor unplugged? Maybe a wheel speed sensor was reading incorrectly? Was it one of a dozen other issues that someone, possibly not even the current technician, had previously had their hands in? Or worse, was an electrical gremlin emerging? This was exactly the kind of nightmare no technician, supervisor, or owner wants weighing on their mind after hours wrenching, especially with no known history beyond what could be seen visually.

The following day, the car was sent for diagnosing at another shop. Those technicians suspected the PCM and ABS Module were causing the problems. Yet, once both were reprogrammed, the issues reoccurred. Two technicians decided to retrace each step and check their work. They confirmed that everything had been completed according to the ALLDATA Repair manual. Tests on the wheel speed sensors and traction control system showed they were functioning correctly. As a last-ditch effort, they manually disabled traction control, leading to the vehicle shifting smoothly for a short time. With no other probable causes presenting themselves, the blame quickly shifted to the transmission. After all, who hasn’t run into a faulty unit right out of the box?

Writing off 8 hours of labor --not including the time spent boxing up another transmission and arranging for its return -- was costly enough. But when the new transmission was installed and the same issues resurfaced, wrenches flew, and tensions rose. That’s when someone suggested calling the ALLDATA Tech-Assist team to help diagnose the problem. The odds of receiving a second defective transmission seemed slim, but the prospect of losing another 8 hours of shop time was even more concerning.

With this information, the technician made a call to the original Ford dealership to see if they had updated anything before starting the work with the possibility of a tire/wheel size mismatch. The dealership verified an issue with programming before the customer had the car removed from the service center. Yet again, the vehicle was taken in for programming this time at a different shop, comparing the unit installed to the vehicle and programming protocol. The problem persisted.

The suggestion from the ALLDATA Tech-Assist team was to monitor vehicle speed readings against the data from the wheel speed sensors. With one hand on the scan tool and the other gripping the ill-tempered Taurus's steering wheel, it was discovered that there was, in fact, a 10-mph discrepancy between the speed indicated on the instrument cluster and the reading from the scan tool.

At this point, the shop placed another round of calls to the transmission builder. While the builder was willing to offer a third replacement, they wanted to dig deeper and verify the VIN and application first. The 17-digits revealed that the transmission should have a 2.77 final drive, not a 3.15 that was ordered. The 3.15 final drive was sending incorrect speed data to the PCM, resulting in mismatched shift points and triggering traction control, which interpreted the discrepancy as wheel spin.

The rebuilder took the original, numbers-matching core transmission and rebuilt it using the correct 2.77 final drive. Once installed, the Taurus performed flawlessly. While the transmission appeared identical on the outside, the internal gearing made all the difference. The lesson? Always verify exact replacement parts, especially when you're facing an 8-hour-plus job to swap them out!