Transmission Control Module (TCM)

The Transmission Control Module (TCM) is the controlling unit for all electronic operations of the transaxle. The TCM receives information from several inputs, and selects the operational mode of the transaxle. Some of the inputs are used only by the TCM, while others are shared with other control modules on the CCD Bus.

Shift schedule logic, which is programmed into the TCM, selects the appropriate shift schedules for operating conditions. This is to determine the desired gear range the transaxle must be operated in. The actual shift points within each shift schedule have been predetermined for the best transaxle operation, and are stored in the TCM's ROM memory.

Once a TCM is installed during service, the following procedures must be performed:
- Quick Learn Procedure - Allows the transmission control module to learn the characteristics of the vehicles transmission.
- Electronic Pinion Factor Procedure - Repro-grams the TCM to compensate for different tire sizes and final drive ratios.

The quick learn procedure is necessary to learn Clutch Volume Index (CVI). The TCM must learn the CVI of the transaxle if it is to be fully adaptive. The quick learn procedure simply speeds up the

TCM learning process. The vehicle must still be driven and shifted several times in each gear range during the road test. This will fully utilize the TCM's adaptive memory capability. The quick learn procedure is accessed through transaxle diagnosis and performed by the DRB Scan Tool.

TCM PROGRAMMING
1. Procedure for flashing the Transmission Control Module with MDS2.

NOTE: THE MDS2 IS REQUIRED TO PERFORM THIS FLASH UPDATE. THE MDS2 MUST BE OPERATING WITH THE LATEST RELEASE INSTALLED. FOLLOW THE PROMPTED FLASH INSTRUCTIONS ON THE MDS2.

2. Procedure for flashing the transmission control module with MDS.

NOTE: THE MDS IS REQUIRED TO PERFORM THIS FLASH UPDATE. THE MDS MUST BE OPERATING WITH THE LATEST RELEASE INSTALLED.

Perform the following procedure for the update:
1. Connect the MDS and DRBIII (Scan Tool) to the vehicle and power them up.

NOTE: FOR THE 1999 MODEL YEAR THE TCM CAN BE REPROGRAMMED FROM THE DIAGNOSTIC DATA LINK CONNECTOR.

2. Use the arrow keys on the DRBIII and from the MAIN MENU screen select MDS DIAGNOSTICS.

3. Use the arrow keys on the MDS and select DIAGNOSTIC MENU from the MDS screen, then press NEXT MENU.

4. Use the arrow keys on the MDS and select VEHICLE CONTROLLER PROGRAMMING, then press NEXT MENU.

5. Use the arrow keys and select PROGRAMMING OF ALL OTHER CONTROLLERS WITH MDS & DRBIII@ on the MDS, then press NEXT MENU.

6. Follow the steps presented on the MDS and DRBIII9, which will allow the DRBIII to obtain the current part number of the PCM.

7. The MDS will display the description of the updatable PCM and/or TCM on the vehicle and the appropriate replacement part number(s). Select the description of the TCM, then press NEXT MENU to begin programming.

8. The MDS and DRBIII@ will prompt for any operator action needed during the remainder of the programming process. If both the PCM and TCM on the vehicle have already been updated, a NO UPDATES AVAILABLE message will be displayed. If this is the case, verify the Authorized Modification Labels attached to the TCM and near the Vehicle Emission Control Information (VECI) label. If the labels are not attached, proceed to step 9. Otherwise, end the procedure.

9. Type the necessary information on the Authorized Software Update Label and attach it to the TCM and cover label with a clear plastic sticker.

CLUTCH FILL VOLUMES (CVI'S)
The L-R clutch volume is updated when doing a 2-1 or 3-1 coast down shift. The transmission temperature must be between 70-120'F. The clutch volume should be between 35 and 83.

The 2-4 clutch volume is updated when doing a 1-2 shift. The transmission temperature must be above 110'F for 99 MY vehicles). The clutch volume should be between 20 and 77.

The OD clutch volume is updated when doing a 2-3 shift. The transmission temperature must be above 110'F for 99 MY vehicles). The clutch volume should be between 48 and 150.

The UD clutch volume is updated when doing a 4-3 or 4-2 shift. The transmission temperature must be above 110'F for 99 MY vehicles). The clutch volume should be between 24 and 70.

To execute the shift logic, the controller must maintain a continuous record of each clutch element apply status. This is done by tracking the instantaneous fluid volumes in each clutch circuit. Instantaneous fluid volumes are tracked using predetermined flow rates and learned "clutch fill volumes". This is particularly useful for closely-spaced shifts or change-mind shifts.

Learned clutch fill volumes represent the volume of fluid that is required to stroke a clutch piston to the point where zero clutch pack clearance is obtained, without stroking the accumulator or picking up any torque load on the clutch. This learned fill volume is updated for each clutch elements as it wears and clutch pack clearance increases.

The DRB, Clutch Volume Index (CVI) display, can be used to view learned CVI's for each clutch. The normal range for clutch fill volumes are shown below
LR = 35-83 2-4 = 20-77 OD = 48-150 UD = 24-70

A transmission which has experienced a sudden clutch failure may not be capable of learning the correct values. A road test of a transmission with this condition may exhibit an upshift runaway condition, but have acceptable clutch fill volumes.

ELECTRONIC PINION FACTOR
A pinion factor is stored in the TCM in order to provide the appropriate distance pulses for a vehicle. The pinion factor is programmed into the TCM at the factory on new vehicles. If a TCM is replaced, the electronic pinion factor must be programmed with the DRB Scan Tool.

The nature of the Electronic Pinion Factor requires that certain features must be taken into consideration:
- If no pinion factor is stored in an installed TCM, the vehicle speedometer will not indicate speed when moving.
- Selecting the wrong final drive ratio or tire size may cause the speedometer accuracy to fall out of specification.
- Use the following procedures to set the electronic pinion factor using the DRB@ Scan Tool:
- Select "Transmission" system, then "Miscellaneous" functions, then "Pinion Factor". The DRB will display the current tire size.
- If the tire size is incorrect, depress the Enter key and then select the correct size.
- Depress the Page Back key to exit the reset procedure.

AUTOSTICK FEATURE
Autostick is a driver-interactive transaxle feature that offers manual gear shifting capability. When the shifter is moved into the Autostick position, the transaxle remains in whatever gear it was using before Autostick was activated. Moving the shifter to the left (towards the driver) causes a downshift, and moving it to the right (towards the passenger) causes an upshift. The instrument cluster will illuminate the selected gear. The vehicle can be launched in 1st, 2nd or 3rd gear while in the Autostick mode. Speed control will be deactivated if the transaxle is shifted to 2nd gear. Shifting into OD position cancels the Autostick mode, and the transaxle resumes to OD shift schedule.

ELECTRONICALLY MODULATED CONVERTER CLUTCH (EMCC)
The use of partial Electronically Modulated Converter Clutch (EMCC) is available at speeds as low as 17 mph, giving the advantage of reducing heat build-up to the transmissions, while buffering the rest of the powertrain from engine torsional vibrations. Full EMCC is utilized under certain conditions to improve gas mileage. Both full EMCC or partial EMCC are also scheduled to help reduce heat build-up of the transaxle or its fluid under certain driving conditions,

Torque converter full EMCC and partial EMCC availability depends on many different input conditions. These include shift lever position (OD, 3, L), current gear range (2nd, 3rd, or 4th), transmission fluid temperature, engine coolant temperature, input speed and throttle angle.

The TCM output logic states controlling the torque converter are the following:
- No EMCC - Torque converter clutch is OFF.
- Partial EMCC - Modulates the LR/CC solenoid (duty cycle) to obtain partial torque converter clutch application. Partial EMCC operation is maintained until full EMCC logic is called for and actuated.
- Pull EMCC - Increases the LR/CC solenoid duty cycle to full "ON" after partial EMCC control brings the engine speed within the desired slip range of transaxle input speed relative to engine rpm (crankshaft speed).
- Gradual-to-No EMCC - Designed to soften the change from full or partial EMCC to no EMCC, at mid-throttle, by gradually decreasing the LR/CC solenoid duty cycle.

A malfunction of the EMCC system is detected from a lengthy partial EMCC operation near the maximum allowable duty cycle, except at heavy throttle. If a diagnostic trouble code is reported, the TCM will not operate the torque converter clutch. It remains unapplied until the next restart. DTC P0740 is stored in memory.

The TCM is provided with EMCC inhibits to prevent EMCC from occurring under specific conditions. The following are times when EMCC WILL NOTE occur:
- Transaxle Temperature - When the transaxle temperature range is warm, cold or supercold, EMCC is inhibited (kept from occurring). In the event of a CCD Bus failure on vehicles not equipped with the Transmission Range Sensor, -3'F is substituted for the initial temperature. This initial value is incriminated up to normal transmission operating temperature based on transmission loading, by monitoring torque converter slip, and input shaft speed. This results in delayed EMCC operation under start-up conditions.
- Brake Signal (ON) - Cancels and prevents EMCC as long as a brake signal is ON.
- Solenoid Switch Valve - If a solenoid switch valve (SSC) malfunction is detected, EMCC will not occur. A SSV diagnostic trouble code will only be stored if the transaxle operating temperature range is hot, and the malfunction occurs at least three times. The fault counter is reset during the start routine.
- EMCC Fault - Any reported EMCC diagnostic trouble code prevents any type of EMCC from occurring.
- Engine Coolant Temperature - If the engine coolant temperature drops below 150'F because of a defective Engine Coolant Temperature (ECT) Sensor, coolant sensor wiring or a stuck open thermostat, EMCC is canceled. PCM diagnostic trouble code (Engine coolant temperature stays low too long) has been known to cause the transaxle to overheat (transmission fluid temperature over 250'F). This causes the TCM to initiate the overheat shift schedule.