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4. LIMP HOME MODE
In case of transmission malfunction ▶
If a serious fault occurs in the automatic transmission, the TCU enters the limp home mode to
secure safe driving and protect the automatic transmission.
As power is no longer supplied to the solenoid, the current basic function (P, R, N, D) is
maintained and the 4th gear can be maintained only by the operation of the hydraulic system
without electrical operation.
The ECU communicates with other electric modules with CAN. If a serious fault occurs, the
transmission automatically enters the limp home mode for service.
The TCU monitors all factors which can affect to the performance of the transmission and
diagnose the system according to OBD II regulation. 1.
2.
3.
4.
In case of overheated transmission ▶
The TCU enters the limp home mode when the batter voltage drops below 8 V.
If the transmission is overheated, the shift pattern is changed to the hot mode to cool the
transmission more efficiently.
While the transmission is overheated, the selector lever symbol and engine temperature warning
lamp on the instrument cluster blink until the transmission is cooled down to the normal operation
temperature. If the transmission is excessively overheated, the gear cannot be shifted but
remains in the neutral position. 1.
2.
3.
Towing the vehicle with A/T ▶
The best way to transport the vehicle is to load it to a truck and transport it, especially if the vehicle is
4WD.
If towing the vehicle with the propeller shaft connected, the transmission or oil pump of transfer case
may malfunction, resulting in internal damage due to poor lubrication. -
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5. ELECTRONIC CONTROL SYSTEM
1) Overview
The transmission control unit (TCU) and its input/output networks control the operations of transmission:
Shift timing
Line pressure
Clutch pressure (shift feel)
Torque converter clutch -
-
-
-
In addition, the TCU receives input signals from certain transmission-related sensors and switches. The
TCU also uses these signals when determining transmission operating strategy. Using all of these input
signals, the TCU can determine when the time and conditions are right for a shift, or when to apply or
release the torque converter clutch. It will also determine the pressure needed to optimise shift feel. To
accomplish this, the TCU operates six variable bleed control solenoids and four ON/OFF solenoids to
control the operations of transmission.
2) Transmission Control Unit (TCU)
The transmission control unit (TCU) is mounted under the driver's seat and controls the operation of the
transmission.
TCU processes the analog information from the internal sensors and the digital information through CAN
communication lines. TCU monitors all the input and output signals. If there is any failure, TCU changes
the system to “Limp Home Mode” and alerts to the driver through the warning lamp on the
instrument cluster.
(1) Hard-wired (Analog) Input/Output
Input/Output Data between TGS Lever and TCU ▶
Position and conditions of gear select lever
Driving moded (Winter or Standard) -
-
Position of inhibitor switch - Input/Output Data between Inhibitor and TCU ▶
6 control signals for variable bleed solenoid
4 control signals for ON/OFF solenoid
Transmission input speed
Transmission output speed
Transmission oil temperature
EMM (Embeded Memory Module) -
-
-
-
-
- Input/Output Data between Automatic Transmission and TCU ▶
Input/Output Data between Self Diagnostic Connector and TCU ▶
Various DTC codes and TCU information -
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ESP OFF switch
Located on the left side of
instrument panel.
Rear wheel speed sensor
Located on the both ends of
rear axle.Front wheel speed sensor
Located on the hub assembly.Sensor cluster
Located at the bottom of center
fascia panel.
Steering wheel angle sensor
Located on column shaft with
contact coil.HECU assembly
Located near the brake booster
in engine compartment and
contains the pressure sensor.
2. COMPONENTS
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2) EBD (Electronic Brake-force Distribution) Warning Lamp (Brake
Warning Lamp)
EBD warning lamp when the system perform the self diagnosis and when it detects the malfunction of
EBD system. However, the brake warning lamp comes on regardless of EBD when the parking brake is
applied.
EBD warning lamp ON:
When turning the ignition switch to ON position, ABS warning lamp and the brake warning lamp
comes on for 3 seconds for self diagnosis and goes off if the system is OK (initialization mode).
When applying the parking brake, the brake warning lamp comes on.
When the brake fluid is not sufficient, the brake warning lamp comes on.
When disengaging the connector, the warning lamp comes on.
When the system is defective, ABS warning lamp and the brake warning lamp come on
simultaneously. 1.
2.
3.
4.
5.
When the solenoid valve is defective
When one or more wheel sensors are defective
When ABS HECU is defective
When the voltage is abnormal
When valve relay is defective a.
b.
c.
d.
e.
When the communication between warning lamp CAN module in meter cluster, the warning
lamp comes on. 6.
3) ESP OFF Indicator
ESP OFF indicator ON:
When turning the ignition switch to ON position, ESP warning lamp comes on for 3 seconds for self
diagnosis and goes off if the system is OK (initialization mode).
When the ESP OFF switch is pressed to turn off ESP function, ESP OFF indicator comes on. 1.
2.
4) ESP Warning Lamp
ESP warning lamp ON:
When turning the ignition switch to ON position, ESP warning lamp comes on for 3 seconds for
self diagnosis and goes off if the system is OK (initialization mode).
When the system is defective, the warning lamp comes on.
When the ESP function is activated, ESP warning lamp blinks with the interval of 2 Hz.
When the communication between warning lamp CAN module in meter cluster, the warning lamp
comes on. 1.
2.
3.
4.
5.
5) ESP OFF Switch
If ESP OFF switch is pressed, ESP function is deactivated and the ESP OFF indicator in the instrument
cluster comes on.
To resume the ESP function, press the switch again. At this time, ESP OFF indicator goes out.
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