Adaptive shift quality technology has been with us since the late 1980’s. Chrysler’s A604 is the most noteworthy trailblazer of this technology. Since then, every manufacturer has followed with their own version of shift quality adaptation. With increased computer processing capacities came more advanced methods for managing shift quality. Of course, with increased complexity comes opportunity for problems to occur. In most cases, when issues arise, most systems will produce trouble codes that point to the area of concern. However, there are a growing number of cases where the shift adaptation process is stopped with no indication that this has occurred. Let’s look deeper into some of these situations and related concerns.
Why Worry About Shift Adapts?
Shift adaptive strategies were designed to extend the life of the transmission by maintaining acceptable shift quality while clutch and band clearances increase due to normal wear. Understanding a manufacturer’s use of shift adapts will help you more accurately assess transmission shift quality issues. Shift adapt data can also help you determine the health of the transmission and engine.
If the shift adaptive strategy is disabled for any reason, the transmission is at risk of premature failure. In most cases, the TCM will command high line pressure and a code will be generated; like P1811 (Maximum Adapt and Long Term Shift) for GM applications. However, there are numerous conditions where there are no codes or obvious drivability symptoms where the adaptive strategy is inactive or disabled. Let’s look into these situations.
A General Overview
Since shift adapt technology relies on “fuzzy logic” from computer data, the root cause(s) may be hard to identify. Here’s a general list of items that can cause the shift adapts to be disabled:
- Coolant Temperature Sensor (out of range, too high, too low)
- Transmission Fluid Temperature sensor (out of range, too high, too low)
- Intake Air Temperature sensor (out of range, too high, too low)
- Cam-to-Crank sensor sequencing not learned (including cam and/or crank sensor signal issues)
- Engine Misfires
- Incorrect engine load signals (including MAF, MAP, exhaust back-pressure sensors, turbo control sensors, etc.)
It is extremely important to note that any of these items can present conditions where the transmission adaptive strategy will not be enabled with no DTCs!
Also, don’t always trust when your aftermarket scan tool tells you that the transmission adapts were cleared or reset. If the shift quality did not change from before to after the reset AND after a test drive at operating temperature, then most likely they did not reset. Some vehicles (like 4 speed automatic Mitsubishi) will require a factory scan tool to reset shift adapts.
Battery Disconnected, Weak Battery and/or Low Charging Voltage
Whenever the negative battery terminal is disconnected on most late model vehicles, the computer system base values are affected. This often requires resetting computer-controlled functions. It may be as simple as initializing the power sunroof auto-stop function on a Toyota application or as involved as re-coding an ECM on an Audi. Always do your homework on items that need to be reset and/ or initialized prior to disconnecting the battery. A search through Alldata, Mitchell On-Demand or any similar database can provide this useful information. When in doubt, use a battery powered memory saving device. Always ensure that the transmission adaptive function is working after changing a battery or removing and replacing the negative battery terminal.
A weak battery can create a scenario similar to a battery disconnect. Unfortunately, they don’t give the iconic “slow, dragging” start symptoms all the time. Today’s engines take far less torque to turn over than their old-school counterparts. Battery voltage can drop as low as 6 volts during cranking, and not give a hint that the battery is weak. At extremely low voltages, the computer systems don’t “wake up” correctly. In most cases, electrical circuit fault codes are the result. In some cases, stored adaptive shift values may be reset to their OEM base values.
A Common Scenario May Look Like This:
The vehicle drives and shifts perfectly throughout the day. However, when it is parked for several hours or after the first start of the day, the shift quality is poor. The vehicle must be driven for several shift cycles, then the shift quality returns to normal.
If you suspect low voltage issues as a cause for shift adapt concerns, back probe the power sources to the TCM and/or PCM to observe the power feed to the computer. Monitor the Keep-Alive power as well as the Ignition Switched power sources using a DVOM or a graphing volt meter. If your feed voltage drops below 10.0 volts during cranking, evaluate your source voltage and any components and/or connectors for issues. Also, your running voltages must be stable and match your battery terminal voltage (unless otherwise noted by manufacturer specifications). Always use the negative battery terminal for your ground reference for all measurements.
Also, look for recent electrical work performed. A new battery and/ or alternator can indicate a possible source of concerns. Check battery capacity (Cold Cranking Amps Rating) and compatibility. Verify the charging voltage of the alternator by using a DVOM. Several manufacturers require special batteries; especially vehicles with start-stop technology.
In the case of most late model BMW applications (late OBD2), you MUST replace the battery with an approved, coded battery. The battery code must be entered by a scan tool into the ECM. Earlier model BMW applications (early OBD2) require a Reset Battery Adapt function so the computer can manage battery charging correctly. These functions also register the battery with the VIN for factory maintenance records. Failure to install a BMW approved replacement battery may affect the transmission adaptive functions.
We always mention how important it is to scan all modules for all codes all of the time. It is especially important to follow this practice when it comes to adaptive shift strategies. Remember, not all codes turn on the check engine light. Some codes may not be read by your aftermarket scan tool. Several manufacturers will not allow transmission adaptive values to be cleared or reset with codes present in ANY module.
For example, I encountered a Mazda application with the Active Adaptive Shift (AAS) system that would not allow the shift adapts to be reset until a code in the Air Bag Control module was cleared!
OBD2 Readiness Tests Not Run or Failed
If one or more OBD2 Readiness Tests have not run or have failed, transmission adapts may not reset or change. These tests show the health of the emission control system, related sensors and the overall general health of the engine.
Vehicles manufactured from 1996 to the present that are sold in the US must comply with the J1979 On-Board Diagnostics standard set by the Society of Automotive Engineers (SAE). When the vehicle computer system is reset (codes cleared) or the battery is disconnected, the OBD monitoring system, which is a built-in, self-diagnostic program, automatically resets and begins a test sequence for the emission control system components.
In many cases, the transmission adaptive function is disabled until the OBD readiness monitors are completed and ready (see figures 1 and 2). You can observe the state of these monitors in mode $06 under the generic scan mode on all OBD2 compliant scan tools or in vehicle specific enhanced diagnostic mode. The vehicle will need to be driven under specific conditions in order to run self-tests.
Here is the Generic OBD2 Drive Cycle Process:
- Ensure that the fuel tank is between 1/4 and 3/4 full.
- Start cold (below 86°F/30°C) and run the vehicle until engine coolant temperature is at least 160°F/71°C (typically requires at least one minute; up to 3 minutes).
- Accelerate to 40-55 MPH at 25% throttle and maintain the speed for five minutes.
- Decelerate without using the brakes (coast down) to 20 MPH or less, then stop the vehicle.
- Allow the engine to idle for 10 seconds. Turn the key off, and wait one minute.
- Restart and accelerate to 40-55 MPH at 25% throttle and maintain speed for two minutes.
- Decelerate without using the brakes (coast down) to 20 MPH or less, then stop the vehicle. Allow the engine to idle for 10 seconds, turn the key off, and wait one minute.
This process varies between manufacturers. In most cases, it takes at least 3 complete OBD2 drive cycles to set all the monitors. Always refer to specific drive cycle routines to ensure the quickest results. Note that most of these functions will occur during normal driving sequences.
One noteworthy example is the Toyota 5 and 6 speed applications. For these, the Monitor Drive Pattern for ECT Test must be completed before adaptive learning is allowed. For example, the 2012 Toyota Tacoma 2WD, equipped with the 4.0L (1GR-FE), V-6 motor and the A750E transmission needs at least a one-half hour drive under specific conditions (see figure 3).
There are numerous companies that produce performance enhancing programming that can be installed in the powertrain control strategy. The increased vehicle performance is usually easily noticed, however, the effects on the transmission strategy may not be obvious.
In many cases, the transmission strategy simply responds to the engine demands, while retaining factory level shift quality. With some tuner packages, the shift strategy program is altered. Further, the performance programming may disable or suppress trouble codes. In all cases, the shift adaptive process may be disabled without your knowledge!
For example, Dodge diesel applications using the 68RFE are notorious for this situation. Before working on these, you want to verify that the adaptations are taking place. A quick, simple process to follow would be:
- Record all the current CVI values on your scan tool.
- With the transmission at operating temperature, perform forced kick downs into each lower gear (6-5, 5-4, etc.)
- Stop and observe the current CVI values relative to the original for changes (Note: The OD Clutch CVI may not change value).
- If the vehicle cannot be .driven, perform a quick learn and observe for CVI value changes relative to the original values recorded.
Note, if the values do not change under any of the above conditions, there is most likely an issue with the programming and/or the PCM. In many cases, simply restoring the OEM programming restores normal transmission adaptation. In some cases, the PCM may not respond correctly, and will need to be replaced. Always review with your aftermarket program supplier before you attempt to reload old software on a new PCM! Just like the OEM, there may be an updated program.
Whenever shift quality is an issue, always look at transmission shift adapts. Diagnostic trouble codes may not be present, however, with an understanding of how vehicle systems interact, you will be able to identify the root cause of your issues. Especially when the transmission doesn’t want to adapt!