Oct. 10, 2002, Ford and GM announced that they would join together to develop a new six-speed front wheel drive automatic transmission. Working on this project together would not only offer a cost-saving factor in its development, they could bring a new transmission to market sooner. Production began in 2006 for a few of their 2007 model year vehicles. Ford builds what they call the 6F35, 6F50 and the 6F55 transmission. GM builds the 6T30/40/45 and 50, as well as the 6T70 and 75 transmissions. The first vehicles Ford placed their transmissions in were the 2007 Edge and Lincoln MKX. GM began using their transmissions in the Saturn Aura, Outlook, Pontiac G6 and the GMC Acadia vehicles.
Interestingly enough, Ford and GM must have enjoyed the experience as they have joined together again to develop an all-new generation of advanced 9- and 10-speed transmissions for cars, crossovers, SUVs and trucks. They expect to go to production in 2016 for some of their 2017 model year vehicles.
A little about GM’s 6T40 transmission (Figure 1) — a second design (Generation 2) arrived in 2012, which consisted of both software and architectural changes. Pressure switches were eliminated from the TEHCM, solenoids went from being variable bleed to variable feed type, and the valve body and many internal parts have changed with Generation 2 design. By this time (2014-2015), all 6T series transmissions should be converted to the Generation 2 design.
SAE International’s 2011-01-1428 paper entitled “Gen 2 GF6 Transmission Hardware and Controls Updates” states that the first generation of transmissions was analyzed for potential enhancements in an effort to increase fuel economy and improved shift quality.
Changes were made with architectural hardware controls in conjunction with system software to increase capacity, reduce system delays (optimize system response times) and increase efficiency.
One example of an architectural change is with the 4-5-6 clutch. The wave plate was removed and an additional friction was added for increased torque capacity (Figures 2 and 3).
With the exception of the Low and Reverse Clutch, each clutch inside this transmission is operated by a solenoid through its respective regulating valve. With Gen 1-based models, a relatively small feed orifice was located on the line pressure supply side of the 4-5-6 Clutch Regulating Valve (Figure 4). With this orifice on one side of the valve and the wave plate on the opposite side of the valve, it stabilized the valve from having a pressure spike when it moved from a full feed position to regulation. When the cushion (wave) plate was removed to add an additional friction plate for increased torque capacity, this orifice was moved to the clutch pressure supply side of the valve (Figure 5). This was done to have a greater control of the apply of the clutch to prevent a harsh engagement with the absence of a cushion plate.
One software change that took place is related to fuel economy, which affects how the TEHCM controls line pressure inside the transmission. Typically, once a shift transition is made, line pressure is increased and held so as to keep the driving or holding clutch from slipping, maintaining the commanded gear. The engine then drives the pump through the torque converter. When line pressure becomes high, this places an additional mechanical load on the engine, negatively affecting fuel economy. For Gen 2, a “system pressure learn” program was written where the computer will periodically bring line pressure down until it sees it slip. It will then raise line pressure just slightly above the slip point, minimizing the margin of safety between slip and non-slip conditions (Figure 6). By doing this, the engine is driving a pump at lower pressures for longer periods of time. This places less load on the engine and thus increases fuel economy.
The line pressure tap is conveniently located on top of the transmission alongside the transmission’s fill cap, as seen in Figure 7. Gen 1 and 2 line pressure specification tables are provided in Figure 8. Specifications were taken from a 2013 Chevy Cruze factory repair manual.
Another software change that took place is related to the elimination of the pressure switches inside the TEHCM assembly (Figure 9). These pressure switches were originally used (Gen 1) to monitor clutch operation via the solenoids and regulator valves for adaptation purposes.
With the elimination of the pressure switches in Gen 2 versions, a new program is used to determine adapts called “Clutch Pulse Learn.” United States Patent Application 20120067690 A1 entitled: Hydraulic clutch and method for determining an adaptive clutch fill volume of the hydraulic clutch provides some insight to its method for learning a characteristic filling volume of a hydraulic clutch. Generally, the method is comprised of:
1. Applies a pressure pulse to a hydraulic clutch when it is in a disengaged state (Figure 10).
2. It determines an inflection event at a torque path that comprises the hydraulic clutch (return spring force).
3. Derives a characteristic filling volume of the hydraulic clutch from the inflection event.
GM factory manuals describes the “Clutch Pulse Learn” strategy as a “Non-Shifting Clutch Function Verification” and describes it as follows:
The 6T30/40/45/50 transmission uses a pressure control system to apply and release clutches during shifts. The transmission control module (TCM) controls pressure commands to the pressure control solenoids.
As normal wear of the transmission clutches occur, the TCM performs a clutch function verification. The TCM momentarily commands a clutch on at a low pressure. The clutch function verification is conducted on smooth roads when the transmission is not shifting and engine torque is consistent and positive.
When clutch function verification is occurring, a slight bump or drag may be detected momentarily. The clutch function verification will occur a few times over several minutes and will not repeat again for a thousand or more miles. This is a normal condition and no repair attempts should be performed.
The clutch function verification will be performed sooner for a particular clutch if the TCM detects it is producing frequent poor shift control.
Transmission Adaptive Values Learn, as most know by now, is a series of tests that are run to allow the transmission control module (TCM) to learn individual clutch characteristics. Once the clutch data is learned, Transmission Adaptive Values Learn translates it into the adaptive data cells, which the TCM uses for clutch control during shifts. The scan tool provides initiation of the Transmission Adaptive Values Learn procedure. This procedure is to be used following transmission repair. The Transmission Adaptive Values Learn procedure must be performed when one of the following repairs have been made to the vehicle. Failure to perform the procedure after one of the following repairs may result in poor transmission performance, as well as transmission DTCs being set:
- Transmission internal service/overhaul
- Valve body repair or replacement
- Control solenoid valve assembly replacement
- TCM software/calibration update
- Any service in response to a shift quality concern
Note: Ensure the following conditions are met before performing the Transmission Adaptive Values Learn procedure:
- Drive wheels are blocked
- Parking brake is applied
- Service brake is applied
- Zero percent throttle and no external engine RPM control
Transmission fluid temperature is between values listed below, if you attempt to run the test above or below these temperatures, the test will not start:
MY 2011 and prior 70-95°C (158-203°F)
MY 2012 Gen 1 70-95°C (158-203°F)
MY 2012 Gen 2 64-95°C (147-203°F)
MY 2013 Gen 1 70-95°C (158-203°F)
MY 2013 Gen 2 64-76°C (147-169°F)
MY 2014 and later 64-76°C (147-169°F)
Transmission gear selector has been cycled from park to reverse three times in order to purge air from the reverse clutches.
Transmission Adaptive Values Learn will abort if the transmission fluid temperature increases to the values listed below:
MY 2011 and prior 110°C (230°F)
MY 2012 Gen 1 110°C (230°F)
MY 2012 Gen 2 100°C (212°F)
MY 2013 Gen 1 110°C (230°F)
MY 2013 Gen 2 86°C (187°F)
MY 2014 and later 86°C (187°F)
Note: If at any time during the procedure, required conditions are not met, Transmission Adaptive Values Learn Adapts may abort and the process may need to be started again from the beginning. If this occurs, the transmission will be left in a neutral state until the controller is shut down, key OFF and the scan tool is removed. Wait for more than 30 seconds prior to re-try procedure. If the procedure repeatedly fails, a limit that engineering set is being exceeded and there is possibly a transmission hardware issue.
1. Use the scan tool to navigate to Transmission Adaptive Values Learn by selecting the following:
1.1. Module Diagnostics
1.2 Transmission Control Module
1.3 Configurations/Reset Functions
1.4 Transmission Adaptive Values Learn
Note: If at any time during the procedure, required conditions are not met, Transmission Adaptive Values Learn may abort and the process may need to be started again from the beginning.
2. Use the scan tool to perform the Transmission Adaptive Values Learn procedure. As the procedure is being performed, the scan tool data display will provide operator instructions. Follow the scan tool instructions, as required.
3. Once the procedure is complete, shut OFF the engine and power down the TCM. You will lose communication to the scan tool.
4. Restart the engine. This will complete the Transmission Adaptive Values Learn procedure.
Note: When the Transmission Adaptive Values Learn procedure is completed, the transmission will remain in a neutral state until the controller shuts down. If after 1-2 minutes of sitting, with the key OFF and scan tool removed, the vehicle remains in a neutral state, disconnect the battery and wait 5-10 minutes and then hook the battery back up. Reverse and drive should return.
If the Transmission Adaptive Values Learn will not run and the above stated conditions have been met, ensure the following:
Note: The generation of transmission can be determined by using a scan tool to check for Specific DTC P0842. If DTC does not show Invalid, the transmission is Gen 1. If DTC shows Invalid, transmission is Gen 2.
- Determine if transmission is Gen 1 or Gen 2.
- Verify vehicle model year.
- Verify transmission fluid temperature is between the temperatures listed above for the
vehicle model year and generation of transmission.
- Brakes and brake switch are functioning properly (Perform Brake Pedal Position
Sensor Learn procedure if necessary).
- No active DTCs
- Closed throttle and engine RPM increases above 1,500 RPM while at entrance of the
test
- Park/neutral position switch is properly adjusted and functioning
- Line pressure control is able to provide 1,000 kPa and is within specifications
- Vehicle is not moving or vibrating excessively
- Clutches are properly assembled
Brake pedal position sensor learn
Note: Do not apply the brake pedal during the brake pedal position sensor calibration procedure. Any movement of the brake pedal during this procedure will cause the calibration procedure to fail. If this occurs, the brake pedal position sensor calibration must be repeated. Brake pedal position sensor calibration must be performed after the brake pedal position sensor, body control module (BCM), or engine control module (ECM) have been serviced. The calibration procedure will set the brake pedal position sensor home value. This value is used by the BCM and ECM to determine the action of the driver applying the brake system and to provide this information to the vehicle subsystems via serial data.
Calibration Procedure
1. Apply the parking brake.
2. Ignition ON, engine OFF, place the transmission in the PARK position for automatic transmission or NEUTRAL position for manual transmission.
3. Install a scan tool.
4. Clear all DTCs before proceeding.
5. Navigate to the Configuration/Reset Functions menu of the BCM.
6. Select the Brake Pedal Position Sensor Learn procedure and follow the directions displayed on the screen.
7. Navigate to the Configuration/Reset Functions menu of the ECM.
8. Select the Learn Functions menu.
9. Select the Brake Pedal Position Sensor Learn procedure and follow the directions displayed on the screen.
