Mitsubishi Eclipse. Technical Information Manual (1994) — part 47

POWER TRAIN

Automatic Transaxle

Electronic control system

Brake switch

Map sensor

I

Speed

Other vehicle

modules

Scan tool
(MUT-II)

Transmission
control module

control

Output speed sensor

relay

Input speed sensor

Four solenoids

Transaxle

Transmission range

pressure switches

and
position switches

TCM Direct Inputs
The direct inputs connected to the TCM are battery
feed, ignition run signal, cranking signal, throttle

sensor signal, engine speed signal (distribu-

tor or

crank sensor signal), input speed sensor

signal, output speed sensor signal, transmission

TCM Indirect Inputs over the CCD Bus
The indirect input signals the TCM senses from
the powertrain control module (PCM) that are sent
over the CCD data bus are, target idle speed, coolant
temperature, battery temperature, brake switch ON/
OFF signal, engine speed (verifies direct input en-
gine speed signal), speed control ON/OFF switch
signal, and the manifold absolute pressure sensor
signal.
As stated earlier, the TCM receives input informa-
tion, and it continuously processes this information

Direct Outputs from the TCM
The direct output signals or output devices the TCM
has control over are, the transmission control relay,

range switch signal, park neutral position switch

signal, low/reverse pressure switch signal, 2-4 pres-
sure switch signal, and the overdrive pressure switch
signal.

through its logic circuits in order to perform all of
the control functions that it has been designed to
perform. However, some of these control functions
are internal to the TCM, while other control functions
are performed when the TCM provides some type
of output signal to another control device. The follow-
ing is a list of outputs related to the transaxle control
system.

the four solenoids in the solenoid pack, and the
vehicle speed signal.

Indirect Outputs from the TCM over the CCD Bus

The only signal sent out from the TCM over the

CCD data bus is communication with the scan tool
(MUT-II) for diagnostics.

POWER TRAIN

Automatic Transaxle

Engine cranking

Scan tool
communication

Transmission
control relay

Transmission Control Module Operation
The main reason for having the transaxle controlled

by the TCM is to have superior shift quality. The
TCM actually “learns” the characteristics of a

(1) Adaptive Memory

The TCM automatically adapts for engine perfor-

mance variations and clutch torque variations to
provide consistent shift quality for the life of the

transaxle. This learning capability is called adaptive

memory. If for some reason the TCM loses its

(2) Quick Learn

A quick-learn procedure is available to pre-program
the shift characteristics into the TCM. The

learn procedure simply speeds up the TCM learning
process. The vehicle still must be driven and shifted

several times in each gear range during the road

TRANSMISSION CONTROL MODULE (TCM)
The Transmission Control Module (TCM), is the brain of the
transaxle. It receives information from several inputs for making
decisions on how the transaxle should function. Some of the

information is used only by the TCM, and some of the informa-

tion is shared with other components through the CCD bus.
The CCD bus is simply a communication link between the
TCM and other electronic components on the vehicle.

TCM Inputs

The TCM uses various inputs to determine when to upshift
or downshift and when to engage or disengage the torque
converter clutch. The TCM also uses these inputs for continuous
feed-back data for controlling shift quality. Without any input,
the TCM has no way to determine the state of the transaxle
and therefore cannot control its operation as designed. The

illustration is a list of the input sensors and signals that the

TCM uses to determine control over its outputs.

TCM Outputs

In order for the TCM to perform, it must have the necessary

number of outputs (signals or devices) that cause the transaxle

to function as desired. Some of these controlled functions (or
outputs) are used by the TCM to cause upshifts or downshifts

(clutch control). Other TCM outputs are information signals

sent across the CCD bus to another control module. The illustra-
tion provides a list of the output signals or devices controlled

by the TCM.

lar transaxle to optimize vehicle shift quality using
its program logic.

memory, through a loss of battery power or the
disconnection of its

connector, it takes

approximately ten shifts for the TCM to re-learn
shift characteristics.

test. This will fully utilize the

adaptive memory

capability. The quick-learn procedure is accessed
through transaxle diagnosis and performed by the
scan tool (MUT-II).

POWER TRAIN

Automatic Transaxle

(3) Self Diagnostics

Another feature of the TCM is that it helps the techni-
cian find a problem within a malfunctioning transaxle
or control system. It can do this through self-diagnos-
tics. When something goes wrong with any of the

(4) Diagnostic Trouble Codes

In addition to sensing electrical malfunctions, the

TCM can also detect some hydraulic and mechanical
malfunctions that also produce diagnostic trouble
codes. Each code represents a different malfunction.

In order to read the diagnostic trouble codes, the

technician must hook-up a special diagnostic scan
tool, called a scan tool (MUT-II). It will be hooked

(5) Default or Limp-In Mode

Another feature of the TCM is the ability to protect
the transaxle from potentially
when certain problems arise. The TCM constantly

monitors its systems. If it senses a problem, it puts
a diagnostic trouble code in memory and shuts down
the electronic controls. When this happens, it is
referred to as default or limp-in. Not all diagnostic

trouble codes put the transaxle into default or limp-in

mode. Only the codes that indicate a problem that

could potentially cause further transaxle internal
damage or hazardous operation. If the TCM fails
for some reason, the transaxle automatically goes

into default.

When the transaxle goes into the default mode,

it automatically shifts to second gear when in any

forward gear selection and stays there. When the

ignition key is turned “off” and then back “on” again,
the TCM resets itself to operate normally until it
senses the fault and again goes into second gear.

major electronic circuits in the TCM and/or its input

sensor and output device network, a two digit numer-
ic diagnostic trouble code is put into memory.

up to a diagnostic connector, located under the
instrument panel.

To retrieve diagnostic trouble codes, it is necessary
to follow the procedures outlined in the Powertrain

Diagnostic Procedures manual for this transaxle.

The TCM can retain up to seven diagnostic trouble

codes in memory at one time.

No matter what forward gear is selected, the vehicle

stays in second gear. Park, Neutral, Reverse, and
Second gear are the only gears that the transaxle
will operate in when in the limp-in mode. The idea
behind limp-in mode is to prevent the customer from

being stranded and to provide them the ability to
drive in (or limp-in) for service.

As mentioned previously in the “Component Identifi-
cation” section, the TCM has the job of controlling
four solenoids in the solenoid assembly. To do this,
the TCM uses its programming and information from
several sensors. Some of the sensors are wired
directly to the TCM and other sensor signals come
from other electronic components across the CCD

bus. The CCD bus is simply a communication link
between the TCM and other electronic components
on the vehicle. The communication link is made
through two twisted wires.

POWER TRAIN Automatic Transaxle

TRANSMISSION CONTROL MODULE INPUTS AND SENSORS

The TCM must depend on receiving information

in order to control shift quality. Let’s take a look

Direct Battery Voltage

There is constant battery voltage supplied to the
TCM, even when the ignition is turned off. This

battery supply is responsible for keeping the
memory alive. If the TCM loses battery voltage at

Ignition Voltage

When the ignition switch is turned to the OFF (col-

umn unlock), the RUN (on), or the Start (crank)
positions, the TCM is activated and looks at incoming

voltage. If the voltage is above approximately 24
volts or below eight volts, the TCM automatically

puts itself in default. Either voltage condition could
damage the TCM.

When the TCM is activated, besides checking the

incoming voltage level, it performs a self-test to
determine if the transmission control relay and the

solenoid assembly are performing as they should.

at what information it receives and how it uses that
information.

any time, it will lose the adaptive memory and have
to re-learn the characteristics of the transaxle for
optimum shift quality.

If the self-test results are good, the TCM sends

battery voltage to the transmission control relay.

The relay closes its internal contacts which supply

battery voltage to the TCM, the four solenoids and

the three pressure switches in the solenoid assem-

bly. Whenever the TCM goes into default, it de-ener-
gize the transmission control relay and prevents
the solenoids from functioning. The solenoids will
then be in de-energized positions, which cause the
transaxle to shift into second gear.

Throttle Position Sensor
The

does not use throttle pressure to control shift points

like previous transaxles did. Instead, an electronic signal from

the Throttle Position Sensor is used by the TCM to help deter-

mine shift points and shift quality.

Engine Speed Signal
Engine speed is supplied to the TCM from the engine crankshaft
position sensor or distributor, depending on the engine and
ignition system used. This signal not only lets the TCM know

the engine is running, but also lets the TCM calculate engine
speed to control torque converter clutch engagement, deter-

mine torque capacity, etc.