There are enough things that happen with late-model vehicles that cause us to scratch our heads and wonder. Some of them border on the definition of a magic act! So, in this issue of “Keep Those Trannys Rolling,” we will take a look at a 2020 Ford Escape equipped with a 1.5L turbo engine and an 8F24 transmission.
This Ford Escape arrived at our shop with the customer concerned about an illuminated malfunction indicator light (MIL) and a “Park not available, apply parking brake before exiting vehicle” message displayed in the instrument cluster panel (ICP). The customer also indicated that the parking brake would automatically engage when the “Park not Available” message appeared in the ICP.
DUPLICATE TO DIAGNOSE
The first step in any diagnostic routine is to duplicate the concern. In this case, it was easy to duplicate the “Park not Available” concern. Each time the Gear Shift Module (GSM) knob (figure 1) was rotated to the “Park” position, the malfunction indicator light would illuminate, and “Park not Available, apply parking brake before exiting vehicle” appears in the ICP.
CHECKING FOR CODES
The next step in our diagnostic path was to scan for all codes in all modules. We connected our scan tool to the vehicle’s data link connector and accessed the vehicle’s onboard computer system. We found code P07E4 (unable to engage park) set in the powertrain control module. There were no other codes listed in any other modules. We cleared the codes and rechecked the transmission operation. Again, each time we rotated the gear shift module knob to “PARK,” the malfunction indicator light would illuminate, and code P07E4 would reset. Since the code was resetting immediately, it was time to look at the transmission park system.
TRANSMISSION PARK SYSTEM OPERATION
The 8F24, 8F35, and 8F40 transmission park system is electro/hydraulically controlled. The transmission park system consists of the powertrain control module (PCM), the park lock pawl solenoid, a parking pawl, an electronic selectable one-way clutch assembly, a manual park release cable, wiring harnesses, and connections. The transmission uses a Park Lock Pawl Solenoid to control the transmission park system hydraulically. The powertrain control module operates the park lock pawl solenoid by de-energizing the solenoid when park is requested. Feedback circuit monitoring inside the PCM verifies that the electrical signal was successfully executed to the solenoid. According to the P07E4 diagnostic routine, this code is set due to a mechanical problem with the transmission park system, not an electrical system problem.
DIAGNOSING THE TRANSMISSION PARK SYSTEM
The diagnostic routine for code P07E4 is pretty straightforward. The first step in diagnosing this code is to confirm that the transmission park system is not being manually or mechanically overridden. Next, we monitored the transmission park status PID (PID TR_PARK_STAT) with our scan tool to confirm the transmission park status. In our case, the transmission park status PID indicated “YES,” which suggests that the transmission park system was being manually or mechanically overridden. If the transmission park status PID had indicated “NO,” that would have indicated an electrical system problem in the transmission park system and set a different code. Now, we need to isolate the cause for the manual or mechanical override of the transmission park system.
ISOLATING THE CAUSE
To isolate the cause of the override, we have to inspect the mechanical components of the transmission park system. First, we must remove the transmission side cover to access the control valve body to access the system. To gain access to the transmission main control valve cover, drain the transmission, remove the air cleaner, underbody shield, remove brackets as needed, remove the start/stop coolant pump, remove the compressor air charge (CAC) hose. Next, reposition wiring harnesses and coolant hoses, disconnect the park manual release cable from transmission (figure 1), disconnect the transmission main harness connector and remove the main valve control cover. We can access the park pawl lock solenoid with the main control valve cover removed. We reconnected the main harness to the main control valve body with the cover off. We were able to observe the function of the park pawl lock system.
While rotating the gear shift module knob in and out of the “PARK’ position, we could hear the park pawl lock solenoid activate (click). We rocked the vehicle back and forth and cycled the park pawl lock solenoid on and off to make sure the transmission remained in park. While the system was working, neither the malfunction indicator light nor the “Park not Available” message appeared in the instrument cluster panel. Everything inside the transmission was functioning correctly. Therefore, the problem had to be outside of the transmission.
The only external component of the transmission park system is the park manual release cable. We reconnected the cable to the transmission lever and retested the system. We found that the transmission would not engage park again, code P07E4 reset in the powertrain control module, and the “Park not Available” message reappeared in the instrument cluster panel. We had isolated the cause of the “Park not Available” concern to a faulty park manual release cable.
CAUSE ISOLATED AND REPAIRED
With the cause of the “Park not Available” concern isolated to the park manual release cable, we inspected the cable for damage and improper routing (figure 2). The cable routing looked good. We removed the left dash end cap and left lower dash panel to access the park manual release cable. The park manual release cable consists of two cables. There is an upper cable and a lower cable. We replaced both upper and lower cables (no adjustment needed), reassembled the dash, and verified the transmission could engage park. We cleared codes from all computer systems and performed our final test drive. After the test drive, we rechecked the transmission park system operation, and it worked perfectly. We delivered the vehicle back to the customer, and it has been working perfectly ever since.
QUICK TIP
From the inspection to repair, the entire process came in at about 6.5 hours. The diagnostic routine and isolation of the cause of concern could have easily been diagnosed by disconnecting the park manual release cable from the transmission. If the transmission parks, the park manual release cable system is at fault for this system. If disconnecting the park manual release cable still gave a no park condition, the issue is inside the unit.
Well, there you have it. We were able to diagnose, isolate and repair a “Park not Available” concern in the new 8F24 transmission. So, with a little patience and maybe a quick tip, you too can “Keep Those Trannys Rolling” down the road.
