6T70/6T75, The Future is Now; Part 4 - ATRA

esents wide open throttle (WOT). This
measurement is very valuable for dealing
with shift feel or shift timing complaints.
Is the CTP value too high or
too low when compared with actual
operating conditions? If so, look for a
problem with a load input such as the
MAP or MAF.
Commanded Gear — Displays
the current commanded gear for the
transaxle: 1, 2-3, 4, 5 or 6.
Driver Shift Control — Displays
either Active or Inactive. The scan tool
displays Active when the gear selector
is in the (M or L) position, which
enables TAP shifting. The scan tool
displays Inactive when the gear selector
is in any range other than M or L and
TAP shifting is disabled. This reading
is important for examining shift timing
complaints. If the display indicates the
system is Inactive, TAP shifting won’t
function.
Driver Shift Request — Displays
the request from the TAP Shift System.
It will display upshift, downshift or
invalid, depending on the voltage level
measured at the BCM/ECM, and will
also display none when there’s no TAP
shift request. Since the TAP switches
are momentary contact switches, an
intermittent wiring or switch problem
could cause the car to shift without customer
input. This reading will help you
verify whether the shift is being caused
by a TAP system problem.
ECT — Indicates the engine coolant
temperature (ECT) value from the
engine coolant temperature sensor. The
ECT reading maximum threshold 151ºC
(304ºF) when the signal voltage is low
(0 volts). The ECT is at its minimum
threshold at –40ºC (–40ºF) when the
signal voltage is high (5 volts). As with
other GM applications, the 6T70 uses a
dual pull-up design for the temperature
sensor circuits. The transaxle uses the
ECT signal for shift timing and TCC
operation. ECT can be used to check the
vehicle’s thermostat operation. A simple
method for verifying ECT operation is
to use a temperature gun and compare
the reading to your scan tool ECT reading.
Engine Speed — Displays the
speed of the engine in RPM. Engine
RPM is a primary input for line pressure
control.
Engine Torque — Indicates a calculated
engine torque based on engine
load, throttle position, and mass airflow.
This is accurate to within 20 Nm (15 ftlb)
of actual measured engine torque.
This is a critical measurement for line
pressure and shift timing control with
the 6T70. It’s also helpful in identifying
aftermarket calibration. If engine
torque under load greatly exceeds the
advertised engine torque rating, suspect
a non-OE calibration.
Gear Ratio — Indicates the calculated
transaxle gear ratio. The scan tool
displays the gear ratio calculated from
the ISS and the OSS speed signals. This
reading is one of the most important
on your scan tool. Check the gear ratio
DO YOU WANT TO GET IN THE
in each gear under load to determine
which solenoids aren’t operating correctly
or which clutches are slipping.
High Side Driver 2 — Indicates
the High Side Driver 2 status. The High
Side Driver controls the power feed for
the solenoids. If the High Side Driver
is disabled the solenoids won’t function.
If the High Side Driver 2 is commanded
off, your scan tool will display
Disabled; if the High Side Driver 2 is
commanded on, it displays Enabled.
High Side Driver 2 CKT Status
— If the voltage is low when the circuit
is commanded on, the scan tool will display
Open/Short to GND. If the voltage
is high when the circuit is commanded
off, the scan tool will display Short to
Volts. If there’s no circuit fault present,
your scan tool will display OK, or
Indeterminate.
Ignition Voltage — Displays the
system voltage.
IMS — Displays PARK,
PARK/REVERSE, REVERSE,
REVERSE/NEUTRAL, NEUTRAL,
NEUTRAL/DRIVE 6, DRIVE 4,
DRIVE 4/DRIVE 3, DRIVE 3,
DRIVE 3/DRIVE 2, DRIVE 2,
DRIVE 2/DRIVE 1, DRIVE 1 or
INVALID. The TEHCM decodes the
binary (high/low) values from the IMS
to determine the actual range selected
by the customer.
IMS A/B/C/P — Displays the status
of the four A/B/C/P IMS pins at the
TEHCM (TCM). HI indicates source
voltage at that specific IMS pin. LOW
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GEARS September 2009 35