> Speed sensor ground circuit short to ground,
short to voltage, or open circuit.
> Temperature Sensor
> TCM
Name of Code: P1738(75) - High Temperature
Operation Activated
When Monitored: Whenever the engine is run-
ning.
Set Conditions: Immediately when the Over-
heat shift schedule is activated.
Theory of Operation: If the transmission oil
temperature rises above 240°F, the overheat shift
schedule is activated refer to the Transmission
Operation as a function of Transmission Oil Tem-
perature. The code is an information code only and
is being set to aid the technician in determining root
cause of customer driveability issue. The code is
also intended to alert the technician to determine if
a cooling system malfunction has occurred or if an
additional transmission air to oil cooler should be
added to the vehicle if the customer regularly drives
in a manner that overheats the transmission. Ex-
tended operation above 240°F will reduce the dura-
bility of the transmission and should be avoided.
Correcting the cooling system malfunction or in-
stalling an additional transmission oil cooler will
improve transmission durability especially for cus-
tomers who operate in city/construction stop and go
traffic, tow trailers regularly, drive aggressively in
low gear or drive regularly in mountainous areas.
Transmission Effects: Information only code.
- Overheat shift schedule was activated, no limp-in
condition occurs. See description of overheat shift
schedule.
Possible Causes:
> Transmission Overfilled with Oil
> Engine cooling fan failure
> Engine thermostat stuck closed
> Radiator corroded or packed with dirt
> Transmission cooler corroded or packed with
dirt
> Transmission fan not functioning properly
> Transmission Oil Cooler Plugged
> Customer driving pattern requires additional
transmission cooling (See Theory of Operation
for typical driving patterns that can cause
overheating)
Name of Code: P1739(76) - Power-Up at Speed
When Monitored: When TCM (Transmission
Control Module) initially powers-up.
Set Condition: If the TCM powers up and senses
a valid forward gear PRNDL code and the output
RPM is above 800 RPM (approx. 20 MPH) the code
will be set.
Theory of Operation: If a vehicle loses power to
the TCM, the solenoids will go to their respective
power off state. Some solenoids are normally vented
and some are normally applied in their power off
state. The transmission is designed to be in 3rd gear
with all of the solenoids in this state. However, if
power is restored, the TCM will power-up and
normal operation will be restored.
This code identifies that power to the TCM was
restored when the gear selector was in a “Drive”
position while the vehicle was moving at speeds
above 20 MPH. This code does not indicate a prob-
lem with the transmission or TCM, instead, it
suggests intermittent problems in the fused igni-
tion switch output, fused B(+), or ground circuits to
the TCM. Alternately, if a person performs a rolling
restart maneuver, the code can be set. Therefore it
is critical that this DTC be investigated if the
vehicle is experiencing intermittent 3rd gear oper-
ation and a subsequent return to normal operation.
Transmission Effects: No limp-in, although the
symptom might be described as an intermittent
limp-in. Code is for information only when trying to
diagnosis intermittent 3rd gear operation and a
subsequent return to normal operation.
> No Problem if vehicle is started in “neutral” at
speeds above 20 MPH and shifted quickly to a
forward gear position.
> Quick key off then on while driving is any
forward gear.
FOR INTERMITTENT 3RD GEAR OPERA-
TION AND THEN A SUBSEQUENT RETURN
TO NORMAL OPERATION WITHOUT CY-
CLING THE IGNITION KEY
> Intermittent Direct Battery (Fused B(+)) con-
nection between TCM (60-way pin 56) and
battery.
> Intermittent Fused Ignition Switch Output
between TCM (60-way pin 11) and ignition
switch.
> Intermittent Ground to TCM (60 way pins 53
and 57).
Name of Code: P-1765(80) - Switched Battery
When monitored: Ignition key is turned from
“off” position to “run” position and/or ignition key is
turned from “crank” position to “run” position.
Set condition: This code is set if the Transmis-
sion Control Module (TCM) senses voltage on any of
the pressure switch inputs prior to the TCM ener-
gizing the relay.
Theory of operation: The Transmission control
relay is used to supply power to the solenoids and
pressure switches when the transmission is in nor-
mal operating mode. When the relay is off, no power
is supplied and the transmission is in “limp-in”
mode. The relay output is fed back to the TCM
15
GENERAL INFORMATION