Transmission Diagnostics; Tcm-Pcm Communication; Gearshift Timing; Warm-Up - Aston Martin DB7 Workshop Manual

The Aston Martin Lagonda Diagnostic System
Users Guide
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Transmission Diagnostics
Automatic transmission DB7s are fitted with a GM4L80-
E gearbox electronically controlled by a Transmission
Control Unit (TCM)
The TCM is mounted on the rear left wheel arch. It may be
electronically accessed from the upper diagnostic socket.
The TCM continuously monitors requests made by the
driver via the gear selector, throttle pedal, mode switch,
etc. This data is used in conjunction with speed input from
the transmission unit to calculate the optimum shift points
undercurrentconditions.Shiftpressureand ignition retard
are also controlled from this data to enhance shift quality
and reduce transmission wear.
TheTCM also detects faults within the transmission system
and stores the relevant fault codes for later analysis.
Gearshifts are controlled by two solenoid valves and a
pressure regulator within the transmission valve block
assembly.
If a serious fault occurs, the TCM removes all electrical
power from these valves and the transmission defaults to
a 'limp home' condition. In this state, only mechanical
selection of either reverse or second gear is available.
Gearshift Timing
Inputs from the performance mode switch (Sport, Normal
or 1st Gear Inhibit) and the throttle position sensor are
used to modify transmission gearshift operation as required
by the driver.
Sport mode raises the roadspeed at which gearshifts occur
enabling higher acceleration rates for the vehicle.
1st gear inhibit prevents engagement of first gear to reduce
the risk of wheel slip in icy conditions.
The throttle position sensor signal is continuously
monitored by the TCM to detect a rapid throttle opening.
If the throttle position sensor signal rises rapidly to above
4.5 volts, a 'Kickdown' condition is initiated. In this
condition, upshifts are delayed to higher road speeds to
provide the higher acceleration required for overtaking
etc.
T C M - P C M Communication
The interface between TCM and PCM allows continuous
exchange of the primary data required to appropriately
control the gearshifts required during driving under a wide
range of conditions.
Powertrain
Control
Module
^.. ^
Warm-Up Signal
Throttle Pot Output
Torque Reduction Request
^ • - - ^
Transmission
Control
Module
Warm-Up
The Warm-Up signal is sent from the TCM to the PCM and
is used to detect when the transmission reaches normal
operating temperature of approximately 100°C (212"'F).
As this temperature is reached, the modified gearshift
timing required with a cold gearbox may be abandoned in
favour of the standard timing for a warm gearbox.
Throttle Pot Output
The ThrottlePot Output signal is sent from the PCM to the
TCM. The TCM can then use this information to control
shift timing in relation to the power demanded by the
driver.
Torque Reduction Request
The Torque Reduction Requestsignai is sent from the TCM
to the PCM. it is used to temporarily retard the ignition
timing during gear shifts to improve shift quality. When the
gearshift is completed, ignition timing will be returned to
normal.
9-40
September 1996