Automatic Transaxle - Shift Characteristics of F4A
NO: TSB-97-23-008DATE: June,1997
MODEL: FA4 A/T models
SUBJECT:
SHIFT CHARACTERISTICS OF F4A SERIES A/T
PURPOSE
Shifting characteristics of the tour-speed electronically-controlled F4A automatic transaxle are not fully described in the service manuals. The F4A series includes the F4A, F4A3, F4A5, and W4A3 transaxles.
This bulletin describes normal F4A transaxle shifting characteristics which may be helpful when diagnosing shifting complaints from vehicle owners.
AFFECTED VEHICLES
Models equipped with F4A automatic transaxle:
1991-98 3000GT
1992-98 Diamante
1994-98 Galant
1995-98 Eclipse
1996-98 Eclipse Spyder
1992-96 Expo and Expo LRV
1993-98 Mirage
SHIFT MODES
Depending on the vehicle model, F4A A/Ts have different types of shift modes at normal, high, and low ATF temperatures. These modes are explained in this bulletin.
POWER/ECONO Modes
The "POWER" or "ECONO" light on the instrument panel will come on when using these shift modes. "ECONO" (meaning economy) is used for most driving situations and provides the best fuel economy. Depressing the A/T MODE button on the shift indicator puts the transaxle in POWER mode. When in POWER mode, the transaxle generally stays in lower gears for a longer period of time before upshifting, and also downshifts more quickly during deceleration.
"Fuzzy Logic" Mode
On F4A transaxles that use "fuzzy logic," the transmission control module (TCM) modifies shift timing for smooth shifting when traveling up and down hills. Artificial intelligence is built into the TCM to automatically simulate the natural shift patterns that a driver would use with a manual transmission. The TCM analyzes inputs from the brake switch sensor, throttle position sensor, and vehicle speed sensor. In addition to the normal A/T shift pattern, "fuzzy" shift controls have multiple shift patterns to suit five different driving conditions: driving on level roads (same as standard A/T mode), driving uphill at low speeds, driving uphill at high speeds, driving downhill in 3rd gear; and driving downhill in 2nd gear.
When driving uphill in "fuzzy logic" shift mode, the transaxle will stay in a lower gear range to maintain power instead of hunting between one gear and another. The TCM takes frequent samples of vehicle speed and throttle opening. It compares each sample with a previous sample to know when to prevent upshifts that would detract from climbing performance.
When driving downhill, it downshifts to provide engine braking without the driver repeatedly pressing the brake pedal. This automatic downshifting is sometimes experienced even when driving on short, gradual slopes or flat roads.
The transaxle will not enter "fuzzy logic" shift mode if the selector lever is not in "D" or if the ATF reaches temperatures specified for High Temperature Mode or Low Temperature Mode. Also, the "fuzzy logic" mode is not used if the ECM judges the throttle position sensor to be operating improperly, or if the transaxle enters fail-safe mode.
INVEC-II (Intelligent Vehicle Control System-II) Mode
Used only on 1997 Mirage and Diamante models, INVECS-II shift control operates similar to "fuzzy logic." It has an added feature of learning the driver's shift pattern preferences. Shift control patterns are modified to favor the driver's style of driving. For drivers who prefer a vigorous style of driving, the transaxle stays in a lower gear until the engine speed becomes relatively high to provide a sporty feel. For drivers who prefer a more leisurely driving style, upshifting occurs at lower engine speeds. For drivers who frequently press the brake pedal when driving downhill, the transaxle downshifts earlier than normal.
If the battery is disconnected, INVECS-II must re-learn the driver's shift pattern preference.
For diagnosis, INVECS-II can be disabled with the MUT-II scan tool.
The upshift pattern chart demonstrates shifting differences with "fuzzy logic" and INVECS-II. The heavy lines indicate normal A/T upshift patterns. The shaded areas indicate the range of speeds at which "fuzzy logic" and INVECS-II controls shifting.
High Temperature Mode I
To avoid ATF overheating, the transaxle enters this shift mode when the ATF temperature reaches above 125° C (257° F) at vehicle speeds below 70 km/h (44 mph). Under these conditions, the transaxle will shift between 1st and 2nd gears only, not into 3rd gear. When the ATF temperature decreases to 110° C (230° F) and under, the transaxle returns to normal shift mode.
NOTE:
On Eclipse models, the ATF temperature for entering High Temperature Mode I is 115° C (239° F). The transaxle returns to normal shift mode when the ATF temperature is 105° C (221° F) and under.
High Temperature Mode II
To avoid ATF overheating, the transaxle enters this shift mode when the ATF temperature reaches above 125° C (257° F) at vehicle speeds below 65 km/h (40 mph). Under these conditions, the transaxle will shift only between 2nd and 3rd gears only, not into 4th gear. When the ATF temperature decreases to 110° C (230° F) and lower, the transmission returns to normal shift mode.
Low Temperature Mode I
When the ATF temperature reaches 20° C (68° F) and below, upshifts are delayed to compensate for the reduced power. The transmission returns to normal shift mode when the ATF temperature reaches above 20° C (68° F).
Low Temperature Mode II
When the ATF or engine coolant is cold, upshifts between 2nd and 3rd gears and between 3rd and 4th gears are delayed to help the catalytic converter warm up more quickly. This condition lasts only one or two minutes after engine start-up.