Today we will talk about the Park Assist System, found on many of today’s vehicles. The Park Assist System is a safety feature in a communications problem. So many of today’s vehicles use control-by-wire systems where the driver doesn’t have direct control of the vehicle. Things like throttle-by-wire and shifter-control motors are commonplace today. In more advanced systems, the brakes and even steering have computer-assist features. So, what happens when the computer loses communication with these systems? It’s time to stop the vehicle before something terrible happens! The Park Assist System does precisely that. When the computer detects a communication problem, it locks the transmission into Park. Let’s get to know this system, noting that not all vehicles operate similarly. The differences in operation from one vehicle to the next could cause a major problem for the operator or the shop involved in the repairs.
The vehicle I would like to talk about is a 2016 ACURA TLX SH-AWD 3.5L model with the electronically controlled ZF9HP48 Speed unit. It is also known as the Q5L9 or the most notorious name, 948TE transmission, used on various vehicles. However, before I move on, I would like to provide a list of vehicles that use this unit (figure 1). Note that these vehicles are found in North America.
Now back to my 2016 Acura TLX 3.5L. When I took the call, I had no idea what problem the technician was handling. Now mind you, the article applies only to those vehicles with the electronic park assist. Some vehicles mentioned in figure one may or may not have the Electronic Park Assist feature, even though they have the same transmission. There are more vehicles with this type of transmission that I did not mention.
So, let me begin by mentioning that this vehicle was stuck in traffic. The technician and the driver/owner of the vehicle reported this issue. The owner claimed that he was driving on a two-lane road and everything was fine until he came up to a traffic light. Then, the driver felt a thump-like movement and the transmission light in the quadrant on the console moved into the park position by itself.
At this moment, the driver lost the ability to move in any direction, the vehicle was stuck in Park, and the shifter would not come out of the Park position. In addition, the car was stuck in the right lane of traffic, making matters worse!
So when the towing company picked up the vehicle, it arrived at the shop on a flatbed. The car could not be pushed off the flatbed because Park would not release, not even with the engine running. Since nothing was obvious, they assumed a mechanical issue occurred inside the transmission. However, codes were pulled, and a DTC P07E6 (Stuck in Park) showed up. Great, but why?
By researching the system of operation for this unit, we discovered this car has the Park Assist feature. So yes, the Park Assist feature was on, but how do we get it out of Park? The factory information explained that when the computer sees an issue with communication, whether it’s a loose plug or a bad connection in the harness, it will automatically go into safe mode. 
Part of the safe mode is to put the transmission in Park electronically. Then, you must manually operate the Park linkage to release the vehicle from Park using a special tool. Figure 2 shows the internal set-up of the Park Assist system inside the transaxle. Also, a website is listed where you can purchase the parkrelease tool. Figures 3 and 4 show the special tool and the corresponding part number.
Remove the Shifter linkage on the transmission to install the tool. Next, pull on the pin with the ring to release the locking mechanism inside the tool. Now turn to the left to achieve the neutral position, and the pin will click into place, maintaining the parking gear off and the transmission in the neutral position (figure 4).
As I mentioned before, not all Park Assist systems operate the same. Back in 2006, the 722.9, a 7-speed Mercedes Benz transmission, was a great innovation, allowing gears to be skipped during upshift and downshift operations, making the vehicle responsive. As a result, the acceleration was much faster, and the vehicles were more fuel efficient. Also, the 722.9 was the first unit that had Park Assist. Unfortunately, with all the good things mentioned, there is no manual way to release the Park Assist linkage inside the transmission! Thankfully, Mercedes created a tool to allow the vehicle to be pushed freely if the car is stuck in Park (Figure 5).
‘Til next time, see ya!
