• Position of selector lever.
• Selected sh ift ran ge.
• CAN sign als.
• Engine Status.
Engine speed lim its may be rea ched in all gear s
with full thr ottle or in kick-down opera tion . In for-
ward driving, the sh ift ran ge of the forwa rd gears
can be adjusted by the opera tor by tipping the selec-
tor lever to the left or right (Aut oSt ick). However, the
TCM feat ures a downshift inhibitor to pr event the
engine fr om overspeeding.
OPERATION
The t ransm ission control modu le (TCM) deter-
mines the cur rent oper ating condit ions of th e veh icle
and con trols the shifting pr ocess for shift comfort and
dr iving situ ations. It receives this opera ting dat a
from sensors and broa dca st messages from other
modules.
The TCM uses inpu ts from sever al sensors that are
direct ly hardwired t o the controller a nd it uses sev-
eral indirect inputs t hat ar e used to con trol sh ifts.
This informat ion is used to act uate t he proper sole-
noids in the valve body to a chieve th e desired gear.
The shift lever assembly (SLA) has several items
that are monitored by the TCM t o calcula te shift
lever position. The r everse ligh t switch, an int egra l
pa rt of th e SLA, cont rols the reverse light r elay con -
trol cir cuit. The Brake/Transmission Sh ift Int erlock
(BTSI) solenoid a nd the park lockout solenoid (also
pa rt of th e SLA) ar e contr olled by th e TCM.
The ECM and ABS broadcast messa ges over the
controller area network (CAN C) bus for use by th e
TCM. The TCM uses this information, with other
input s, to det ermine the tra nsmission operat ing con-
ditions.
Th e TCM:
• det ermines the mom enta ry operatin g condition s
of the vehicle.
• controls all shift pr ocesses.
• considers shift comfor t a nd t he dr iving sit uation.
The TCM con trols th e solen oid valves for modulat-
ing shift pressu res and gea r changes. Relative to the
torqu e bein g transmitted, the r equired pressur es are
calcu lated fr om load con ditions, en gine rpm, veh icle
speed, an d ATF temperatu re.
The following fu nctions ar e conta ined in the TCM:
• Shift Program
• Downshift Sa fety
• Torque Converter Lock-Up Clu tch.
• Adaptation .
This transmission does not ha ve a TCM rela y.
Power is supplied to the SLA and the TCM directly
from the ignit ion.
The TCM con tin uously checks for electr ical prob-
lems, mechanical problems, and some hydr aulic pr ob-
lems. Wh en a problem is sensed, th e TCM stores a
diagnostic trouble code (DTC). Some of these codes
cause the tr ansmission to go into “Limp-In” or
“defau lt” mode. Some DTCs cause permanent
Limp-In and others ca use temporary Lim p-In. Th e
NAG1 defaults in the cur rent gea r position if a DTC
is detected, t hen after a key cycle th e tran sm ission
will go into Limp-in , which is mech anical 2nd gear.
Som e DTCs may a llow the tra nsmission to r esu me
normal oper ation (recover) if t he det ected problem
goes a way. A permanent Limp-In DTC will recover
when the key is cycled, but if the same DTC is
detected for t hree key cycles the syst em will not
recover and the DTC must be cleared from t he TCM
wit h t h e DRBIII ! scan tool.
TCM SIGNALS
The TCM registers one part of th e input sign als by
direct input s, th e ot her pa rt by CAN C bus. In addi-
tion t o th e direct control of th e actu ator s, the TCM
sends va rious output signa ls by CAN C bus to ot her
control modules.
Selector Lever Position
The TCM m onitors t he SLA for all shift lever posi-
tions via th e CAN bu s.
ATF Te mpe r a t ur e Se nsor
The ATF tem perat ure sen sor is a positive temper-
ature co-efficien t (PTC) thermistor. It mea su res th e
temper ature of the tra nsmission fluid and is a direct
input signal for the TCM. The tempera ture of t he
ATF has a n in fluen ce on the shift time an d resu lting
sh ift qua lit y. As the tempera ture rises, resista nce
rises, a nd therefor e, the probing volt age is decr eas-
ing. Because of its registration, the shifting process
can be optimized in all tem per atu re ra nges.
The ATF tempera ture sensor is wired in series
with the pa rk/neut ral cont act. The t empera ture sig-
nal is tr ansmitted to th e TCM only when t he reed
contact of the pa rk/n eutr al contact is closed becau se
the TCM only rea ds ATF tempera ture wh ile in an y
forwar d gear, or REVERSE . When the tra nsmission
is in PARK or NEUTRAL, the TCM will subst itute
the engine t empera ture for the ATF tempera ture.
Starter Interlock
The TCM monitors a con tact switch wired in series
with th e transm ission tem per ature sensor to deter-
mine PARK a nd NEUTRAL posit ions. The contact
switch is open in P ARK and NEUTRAL. The TCM
senses transmission tempera ture as high (switch
su pply volt age), confirming swit ch st atus as open.
The TCM then broadcasts a message over CAN bus
to confirm swit ch status. The PCM receives this
information a nd allows operat ion of the sta rter cir-
cuit.
VA ELECTRONIC CONTROL MODULES 8E - 7
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