Isuzu KB P190. Manual — part 949

Automatic Transmission – 4L60E – Electrical Diagnosis

Page 7C2–10

Limp Home Mode Description

If a major electrical system failure occurs which could affect vehicle safety or damage the transmission during normal
operation, the TCM enters a limp home mode. In the limp home mode, the transmission operates in the following
manner:

•

The pressure control solenoid is off and the line pressure is at maximum to minimise clutch slippage.

•

The TCC solenoid is off, therefore the torque converter clutch is disabled.

•

The two shift solenoids are turned off. The transmission will operate in fourth gear if the vehicle has successfully
completed a 1-2 upshift in the current ignition cycle. If the vehicle has not completed a 1-2 upshift in the current
ignition cycle, the transmission will operate in third gear. If the transmission is operating in fourth gear, third gear
may be obtained if the engine is stopped briefly and re-started.

In limp home mode, the gear selector lever is ineffective at selecting forward gear ranges. In third or fourth gear, heat
builds up in the transmission quickly, particularly in stop and go traffic. Excessive heat build-up may cause transmission
failure if the vehicle is driven for extended distances in limp home mode.

1.3

Transmission Indicators and Messages

For information pertaining to the instrument cluster and the transmission information it displays, refer to the RA Rodeo
Owner Handbook.

1.4

Electronic Component Description

For all other electrical components not covered in this section, refer to General Motors Powertrain Group Electronically
Controlled Automatic Transmission Technician's Guide.

Transmission Control Module (TCM)

The Transmission Control Module (TCM) is located under the instrument panel, next to the brake pedal assembly and
connects directly to the transmission wiring harness. A single 49-way connector is used to make the connection between
the vehicle wiring harness and the TCM.

To access the connector for diagnosis:

1

Ensure the ignition switch is in the OFF position.

2

Disconnect the connector (1) from the transmission control module (TCM) (2) as follows, refer to Figure 7C2 – 2:

a

remove the securing pin (3),

b

press the locking tab and swing the lever (4) to free the connector,

c remove

the

connector.

Automatic Transmission – 4L60E – Electrical Diagnosis

Page 7C2–11

Figure 7C2 – 2

The TCM is an electronic control module receiving input or providing output to control the operation of the 4L60E
automatic transmission.

The TCM receives the following inputs from the engine control module (ECM):

•

engine speed and torque values,

•

engine intake air temperature (IAT), accelerator pedal position (APP) information,

•

engine coolant temperature (ECT),

•

driver selected shift mode, and

•

air-conditioning (A/C) status.

The ECM provides this data to the TCM through the databus.

Other TCM inputs are:

•

battery and ignition voltage,

•

brake switch status,

•

transmission fluid temperature (TFT), and

vehicle speed sensor (VSS).

The TCM provides the following outputs to control the automatic transmission:

•

shift solenoids to control transmission shifting,

•

torque converter clutch (TCC) pulse width modulated (PWM) solenoid operation to control the apply and release of
the torque converter clutch assembly, and

•

pressure control (PC) solenoid to regulate the transmission line pressure.

Other TCM outputs provided to the ECM / PIM are:

•

MIL illumination request,

•

vehicle speed,

Automatic Transmission – 4L60E – Electrical Diagnosis

Page 7C2–12

•

transmission fluid temperature,

•

commanded gear status,

•

TCC status, and

•

torque reduction requests.

Automatic Transmission – 4L60E – Electrical Diagnosis

Page 7C2–13

2

Wiring Diagrams and Connector
Chart

For wiring diagrams and connector information, refer to 8A Electrica-Body and Chassis.