TASC Force Tips

• Author: Jeff Parlee

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In the United States, the AW55-50 is used in the:

As you can see, there are a lot of these transmissions on the street. It is important that you understand what a normal operating condition is and what is not normal for the vehicle that you are working on. Not all AW55-50 transmissions have the same operating features.

For example, Saturn has eight operating modes or shift strategies. They are normal mode, protection mode, cold mode, hot mode, uphill mode, downhill mode, high-altitude mode and traffic-jam mode. Each of these modes has a different shift strategy. The customer is familiar with normal mode and may have noticed cold mode. The other modes don’t show up very often and, if noticed, may be seen as a very intermittent problem.

You may have a customer come in with a Saturn that has a complaint of second-gear starts or seems sluggish with a lack of power from a start. The customer says that this happens only once in a while. You could spend a lot of time trying to diagnose this normal condition if you don’t know that the computer is commanding the shifts in traffic-jam mode.

Some Volvo models have a neutral-control feature. The computer turns off the C1 clutch when the vehicle comes to a complete stop for more than two seconds with the brake applied. This is a feature that the customer should never feel, but quite frequently you will get a harsh re-engagement and sometimes a downshift thud when the C1 clutch releases. Volvo has software updates to fix this as well as flared 2-3 shifts, harsh downshifts and harsh garage shifts. Most manufacturers have software upgrades for this transmission. Check with your local dealer for the latest upgrades available for your application.

As with almost all newer transmissions, the AW55-50 relies on adaptive strategy to adjust the shift feel for each shift. Whenever the transmission is overhauled or replaced, or the valve body or transmission control module (TCM) is replaced, the shift adapts must be cleared and relearned.

Failure to perform these procedures can result in shift-feel and downshift-clunk complaints, as well as reduced transmission life. Some vehicles relearn slowly and require a dealer-equivalent scan tool. You don’t want to damage your fresh overhaul waiting for the computer to relearn its adapts.

The challenge presented by having multiple manufacturers using the AW55-50 is that you need to be aware of the different operating modes and different relearn techniques. Understanding the operating system and procedures for each vehicle and knowing which bulletins and updates are available will go a long way toward fixing the car right the first time and keep you from wasting your time.

Next month we will cover the adaptives and their relearn procedures along with some known bulletins you should be aware of. For now, let’s have a look at the variety of operating modes. As mentioned, GM/Saturn strategy augments the normal operating mode with seven additional modes as follows.

GM/Saturn shift modes

Protection mode – This is like failsafe or limp-in mode in other vehicles. When the protection mode is tripped by a code you will have fifth gear in drive and intermediate. When in manual low you will have second gear. Cycling the ignition will restore normal mode until the code is set again.

Cold mode – When the engine coolant temperature is less than 122˚ F, shifts will occur at a higher speed.

Hot mode – When the transmission-oil temperature reaches 284˚ F, the computer applies the converter clutch at lower-than-normal speeds and raises the shift points to a high speed. When the transmission-oil temperature drops below 270˚ F, normal mode will resume.

Downhill mode – When the throttle angle is less than 3% and vehicle speed is increasing, the computer will command higher shift speeds to provide more engine braking.

Uphill mode – When engine load is high and vehicle speed is decreasing, the computer will command higher shift speeds.

High-altitude mode – When barometric pressure is less than 12.76, the computer will command higher shift speeds.

Traffic-jam mode – When the vehicle stops and starts with less than 10% throttle angle, the computer commands second-gear starts to increase fuel economy and reduce shift busyness. Normal mode resumes when throttle angle is greater than 30% or vehicle speed is greater than 18.6 mph.

Volvo shift modes

Economy mode – The TCM uses this mode under normal acceleration, providing the earliest possible upshifts and lockup for best economy. The TCM adjusts oil pressure to provide smooth shifts and engagements.

Sport mode – The TCM changes from economy to sport mode if the accelerator pedal is depressed quickly and the vehicle exceeds 31 mph. Sport mode raises the shift points to provide the best performance, and downshifting occurs at lower engine speed. When the accelerator pedal is moved less quickly, the TCM resumes economy mode automatically.

Extreme mode – Extreme mode is another way of saying kickdown. The TCM selects the lowest possible gear for the vehicle speed when the accelerator pedal is pressed to the floor.

Winter mode – Winter mode is selected by using the “W” button on the top panel of the gear-selector assembly, and a warning lamp in the instrument cluster illuminates. In winter mode, the transmission will start in third gear to provide maximum traction on slippery surfaces. Depending on manual gear selection, the following shift combinations can be obtained:

• D – The transaxle starts in third and automatically shifts to fourth and fifth gears.
• 4 – The transaxle starts in third and automatically shifts to fourth earlier than in economy-mode in D range. Fifth gear is locked out.
• 3 – The transaxle starts in third and does not upshift or downshift.
• L – The transaxle starts in second gear and does not upshift or downshift.

At wide-open throttle in winter mode, the transaxle uses all gears for maximum performance.

Catalytic-converter start – This function helps the engine reach operating temperature by preventing torque-converter lockup and delaying the 1-2 and 2-3 upshifts when the engine is cold. This is a normal function.

Temperature-controlled lockup – If the transmission temperature rises excessively as a result of a heavy load with high ambient-temperature conditions, the torque-converter clutch (TCC) is applied to reduce heat generated by the torque converter. If the temperature drops below 20˚ C (68˚ F) lockup will be inhibited.

Slipping lockup – Slipping-lockup mode allows for a smoother lockup engagement while reducing vibration and noise. The computer maintains TCC slip of 50-200 rpm in this mode.

The following conditions must be met for this mode to activate:

• Shifter must be in the D, 4 or 3 position.
• Transmission must be in third, fourth or fifth gear.
• The transmission input speed must be 1,100 rpm or higher and throttle opening must be 35% or less.
• Engine coolant must reach a certain temperature.
• Transmission-oil temperature must be at least 40˚C (104˚ F), but not exceed 120˚ C (248˚ F).

Note: The friction properties of this transmission fluid are different from those of other fluids because of the large amount of TCC slip. Failure to use the correct fluid will cause transmission damage and codes.

Driving uphill – To reduce shift busyness, the TCM may change the shift pattern slightly when the vehicle is going uphill.

Neutral control (not available on all models) – With this function, the TCM disengages the forward clutch (C1) at a stop with the brakes applied. This reduces the load on the engine, thereby reducing engine vibration and improving fuel economy. When the brake is released the forward clutch engages. The following conditions must be met before the neutral-control function will be allowed:

• Manual shifter must be in D, 4 or 3. Neutral control will not work in winter mode or when Geartronic is selected.
• Transmission-oil temperature must be above 10˚ C (50˚ F).
• Throttle position must be less than 3%.
• Brake pedal must be depressed.
• Vehicle speed must be zero mph.
• Engine speed must be less than 1,500 rpm.
• There is a two-second delay once the vehicle has stopped in the D position and a five-second delay when the transaxle is shifted from N to D.

Shifting using Geartronic

When the shifter is moved to the Geartronic position, the transmission remains in the hydraulic D position. When the shifter is moved to the + or – position, the gear-selector module sends a signal to the TCM to shift the transmission up or down. The driver-information module changes the symbol on the instrument cluster from D to the gear that has been selected. A signal is sent to the gear-selector module to light the M and turn off the other LEDs on the shifter console. The TCM determines whether the shift can be carried out and activates the appropriate solenoids. The TCM will override the driver’s command under certain circumstances. The following applies during Geartronic shifting:

• Only first, second or third gear can be selected from a stop. The transmission will not upshift into fourth until vehicle speed reaches at least 19 mph. The transmission will not upshift into fifth until vehicle speed reaches at least 25 mph.
• Automatic downshifting occurs below certain speeds if the driver forgets to manually downshift. Manual upshifting is required after automatic downshifting has occurred.
• Kickdown is not available in Geartronic mode.
• The TCM will not allow the transmission to be manually downshifted if engine speed would exceed 6,000 rpm.
• If transmission temperature gets too high, the TCM will select the correct gear to enable lockup.
• Torque-converter lockup is possible only in third, fourth and fifth.

Nissan shift modes

Downslope mode – The TCM detects downhill driving when vehicle speed increases with a closed throttle. During downslope mode the TCM changes the shift points for more engine braking.
Upslope mode – The TCM detects uphill driving when engine load is high and vehicle speed decreases. Upslope mode raises normal shift points to avoid busy shifting.
Hot-mode control – When transaxle temperature gets too high (Nissan gives no specification), the TCM changes the shift points to reduce transaxle temperature.
Manual mode – When the manual shift lever is moved to the manual shift position, the driver can manually upshift and downshift. The TCM will automatically upshift the transaxle if the engine exceeds a specified speed. The TCM will automatically downshift the transaxle if vehicle speed falls below a specified value to avoid transaxle damage. The TCM will control TCC operation at all times.

Saab shift programs

Manual-shifting program – Manual shifting can be accomplished by moving the manual shift lever to the M position. The driver then can control upshifts and downshifts using the + and – buttons on the steering wheel. The TCM will override the manual controls if engine speed gets too high and the driver has not commanded the shift or forgets to downshift when vehicle speed drops below the threshold for the selected gear. The TCM will not allow the driver to downshift manually until vehicle speed drops below a predetermined point for the particular gear. The driver can start from a stop in first, second or third only. The manual feature can be used even when cruise control is on.

Temperature program 1 – Temperature program 1 is activated when transmission-fluid temperature exceeds 125˚ C. Lockup is activated in third and fourth with no converter slip, and shifts are at higher speeds to cool the transmission fluid. When the fluid temperature drops below 120˚ C, temperature program 1 deactivates. Temperature program 1 will not activate when the TCM is in limp-home.

Temperature program 2 – Temperature program 2 is activated when transmission-fluid temperature exceeds 135˚ C. This program forces upshifts at even higher speeds, and converter lockup occurs more often than in temperature program 1. Lockup is commanded on with no slippage during this program. Temperature program 2 deactivates when fluid temperature drops below 127° C, and temperature program 1 resumes.

If fluid temperature rises above 155˚ C for more than two seconds, code P0218 is set, the temperature is recorded, the “CHECK GEARBOX” light does NOT light and the TCM sends a bus message of “TRANSMISSION OVERHEATING,” which is shown in the PID display. Engine torque is reduced to a maximum of 200 Nm to protect the transaxle.

Special gear-change program – A special gear-change program is automatically activated if a high load is detected. Upshifts and downshifts will occur at higher engine speeds to keep the fluid from overheating. Examples of when this program would engage are driving up long hills and towing a trailer. The special gear-change program will not initiate above 150 km/h (93 mph).

DPS program – Differential-protection system reduces engine torque during extreme wheel spin. DPS will activate only below 80km/h (49.6 mph). 150 Nm is the maximum engine torque allowed during DPS activation.

Reverse-inhibit program – A reverse-inhibit feature will turn on the S1 solenoid, which releases the B3 brake, if the TCM detects that the vehicle is moving at 7 km/h (4.3 mph) or faster.

Reading about all these modes makes it easy to see many possible intended or normal functions that could be mistaken for a functional problem. You will need to consider these modes carefully during your diagnosis, just as you will need to work carefully with relearn strategies when you complete a repair. We will cover those next month.

Jeff Parlee is director of product support at Valve Body Xpress and a member of the Sonnax TASC Force (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax Industries Inc. technicians.