As technology advances, transmissions evolve to provide greater versatility and efficiency for powertrain management and customer driveability satisfaction. The 9T50 is General Motors’s choice for next-level performance that adapts to the needs of the powerplants in their front-wheel drive vehicles. A by-product of co-engineering with Ford, the 9T50 shares design features with the 8F35 and the 6-speed predecessors. However, despite similarities, noteworthy differences come into play when diagnosing these units for issues. In this article, we will give you some essential tips on handling these units when they come to your shop with issues.
VARIANTS
The 9T50 is used in several GM applications (figure 1). Identifying the transmission type is just as important as verifying and finding the complaint. Utilizing the QR label on the vehicle’s B-pillar is a surefire way to positively identify the unit in your car. The 9T50 designation is typical for this family of transmissions.
Other variants with lower or higher torque capacities are denoted by a difference in the trailing two digits. Note that there can be a variation in shift-by-wire, shift-by-cable, first- or second-generation transmissions within the different unit torque capacities. The other possibilities can only be identified by the RPO code and vehicle identification number, so order all transmission parts based on these two numbers!
ELECTRONIC TRANSMISSION RANGE SELECT
GM has used a shift-by-wire system in its front-wheel and rear-wheel drive applications for several years. The 9T50 family can be equipped with either a shift-by-wire or shift-by-cable system. GM’s shiftby- wire system is quite a bit more complicated than others on the market. Understanding the system operation is critical for diagnosing malfunctions when they occur. Some use a conventional-looking shift lever, while others use push buttons on the dash for driver control. Keep in mind that either configuration has no shift cable or physical connection between the shifter and the transmission. GM refers to its system as ETRS or Electronic Transmission Range Select.
Four different ETRS designs are in use: GEN 1 internal, GEN 1 external, GEN 2 internal, and GEN 2 external. The primary difference between the systems revolves around which module controls the system function and which stores the DTCs when one sets.
To understand the system operation, let’s look at the 9T50 applications equipped with ETRS. Seven components comprise the system for the 9T applications (figures 2a – 2d). These include the following:
- Park Inhibit Solenoid: The solenoid acts as a safety system to mechanically hold the park servo in the released position if hydraulic pressure is lost to the transmission. This system prevents the park pawl from engaging as long as vehicle speed is present.
- Mode 1 ETRS Valve: This valve controls pressure to the Mode 2 Valve. In Drive and Reverse, it directs pressure to the Park Release Servo Valve Plunger to shift the transmission out of Park.
- Range Select Valve Position Switch: This switch monitors the position of the Mode 1 Valve.
- Park Release Servo: Mechanically controls the park release lever and park pawl actuator.
- Park Servo Position Switch: Tells the controller the position of the Park Release Servo Piston Plunger
- Mode 2 ETRS Valve: Works with the Mode 1 ETRS Valve to control the Park Release Servo Piston Plunger.
- Mode Valve Position Switch: Used to monitor the position of the mode valves.
The ETRS system uses feedback from the Mode Valve Position, Range Select Valve Position, and the Park Servo Position switches to determine if the mode selected by the driver matches the hydraulic selection inside the transmission. If it does not agree, a message is displayed in the Driver Information Center and the vehicle may default to Park, depending on the fault detected. Most faults will also be accompanied by TCM, ECM, and/or BCM diagnostic trouble codes.
DIAGNOSIS BY SYMPTOM
Some of the most basic transmission-related complaints can put you into a tailspin if you are not aware of the basic functions of the transmission control systems on the 9T50 unit. Understanding and verifying the customer complaint is extremely important on the diagnostic side of these units. A simple no-move complaint can turn into a unit being pulled unnecessarily. Let’s look at some new control systems for the 9T50 applications.
First things first, always scan all modules for codes and record all codes in all modules! This is especially important with vehicles equipped with the ETRS system. Several faults related to the ETRS operation will produce a no-move or stuck-in-park complaint.
A helpful tool built into the vehicle is the Driver Information Center (DIC). Observe messages that appear here that could direct you toward faulty components or systems. Note that the driver’s door and seat switches are used to determine if the vehicle is safe to operate in gear. If the door switch opens or the seat switch shows no one is in the driver’s seat, gear selection will be inhibited.
Also, vehicles with the 9T50 unit use a new default strategy incorporating the driver’s seatbelt switch with the gear select function. The vehicle will not go into gear until the seatbelt is buckled. However, you can wait ten seconds after starting the car, allowing you to select a range of operation.
For vehicles equipped with the ETRS system, GM provides service modes to operate the vehicle for diagnostic purposes only. Here’s one crucial mode for diagnosing no-move or stuck in Park complaints. If the vehicle defaults to Park, you can depress the brake, hold the shift select button on the shifter, and place and keep the shifter in the desired range. The vehicle should engage (if it is able to move) in that range as long as you hold the select button and shifter in the selected range. Releasing the select button and shifter will place the vehicle into Park.
GEARTRAIN FAILURES
Shared technology and engineering give this unit an edge on parts reliability. However, even though this transmission is similar to the 6T40, this unit has issues with output planetary failures. Using a stethoscope or similar listening aid can help in diagnosing related issues. Inspect and replace the planetary as needed during a bench inspection. Refer to technical service bulletins that may apply to known defective parts for specific applications.
VALVE BODY
The valve body is a sensitive part of this unit. The Direct Acting solenoids and the control valves are highly vulnerable to debris. Fine metal and debris enter the solenoid and cause the pintel motion to be intermittently restricted. The control valves do not have return springs acting on them. They rely on the pressure from the bottom land of the valve to push them towards the solenoid. Debris causes these valves to stick. Issues with the Direct Acting solenoids and the control valves result in the following shift quality issues:
- Flared or slipping shifts.
- Harsh or binding shifts.
- Missing shifts.
The retaining clips that hold the Direct Acting solenoids are made of spring metal. The clips tend to loosen and allow the solenoids to move in the bore during operation. In extreme cases, they can break. Always replace or repair these clips when servicing the valve body or rebuilding the transmission. There are aftermarket solutions available through your soft parts supplier. Also, Ford carries these clips in their parts department (Ford part number HL3Z-7G007-A, verify four clips per package). These clips also service Ford and GM rear-wheel drive 10-speed units and Ford 8F transaxles.
The ETRS-equipped valve bodies are more susceptible to problems. Since this is a wireless system, the operation of the actuators and the feedback switches are critical to determining if the transmission is allowed to move by the computer programming logic. Metallic debris suspended in the fluid is attracted by the magnets inside the Hall Effect switches (figure 3). Excessive metal can cause the switch to give incorrect feedback to the TCM, forcing a default strategy (stuck in Park). In extreme cases, the cavity where the valve interacts with the switch can become restricted, causing the end of the valve to break or the magnet in the switch to break. During a bench inspection, it is important to break the valve body down to inspect these valves and switches.
REPAIRING THE UNIT
In some cases, a target repair is in order. In other cases, a complete overhaul is necessary. Determining which route to take may not be clear, so here is a recommendation. If the fluid does not show excessive debris or mechanical issues, a valve body service may be in line. First, drain the transmission fluid into a clean container. Since there is no sump, use a zip tie, mechanic’s wire, or a magnet to insert into the drain hole to see if there is excessive debris in the bottom of the unit.
If you determine the unit must be overhauled due to excessive debris, be prepared to assess the internal components thoroughly. As previously mentioned, the output planetary assembly may be the source of debris in the unit. Check the planetary pinions for excessive rocking movement. Replace as needed.
Also, you will need to address the Selectable One-Way Clutch (SOWC). Excessive debris can cause the unit to have a bind on the 1-2 shift. Fine debris accumulates inside the rotating plate areas where the assembly is supposed to freewheel. You can service this unit by completely disassembling and cleaning it thoroughly. However, I recommend having a completely clear work area and small parts containers for the individual dogs and springs in the one-way assemblies. Of course, this will take time, so advise your sales manager to at least get an hour for your labor!
Transmissions with more than six speeds still seem out of the scope of regular units you expect to work on in your shop in the near future. However, these units are proving to be at your doorsteps sooner rather than later. ATRA is doing everything to keep you informed so that you can confidently deliver the goods to your customers!
