Isuzu KB P190. Manual - part 1109

7A2-152   TRANSMISSION CONTROL SYSTEM (JR405E)

Output Shaft Speed (OSS) Sensor

Legend

1. OSS sensor
2. Parking gear 

The output shaft speed (OSS) sensor is located on
right-hand of the transmission case near the
transmission range switch. The OSS sensor is a hall
effect element type sensor, which generates a square
wave signal pulse based on the parking gear rotational
speed that is connected to output shaft (16 pulses per a
rotation of the parking gear that is fitted with the output
shaft by spline). The TCM calculates the vehicle speed
by the OSS sensor signal, and uses it to determine
appropriate shift points and calculate gear ratio. The
2WD vehicle outputs the vehicle speed signal from the
TCM to the engine control module (ECM) and the
vehicle speed meter via output signal line.

Transmission Control System Description

Transmission Control Module (TCM) Service
Precautions

Important:
To avoid shock and possible serious injury, DO NOT
touch the terminals. When disconnecting the harness
connectors, always turn OFF the ignition switch or
disconnect the battery cable.

The transmission control module (TCM) is designed to
withstand normal current draws associated with vehicle
operation. Avoid overloading any circuit. When testing
for opens and shorts, do not ground or apply voltage to
any of the TCM circuits unless instructed to do so. In
some cases, these circuits should only be tested using
a DMM. The TCM should remain connected to the TCM
harness. The TCM is located next to brake pedal via
mounting bracket. The TCM mainly controls the
gearshift system control and on-board diagnostic for
transmission control. The TCM constantly observes the
information from various sensors. The TCM controls
the systems that affect vehicle performance. The TCM
performs the diagnostic function of the system. The
TCM can recognize operational problems, alert the
driver through the check trans lamp, and store
diagnostic trouble codes (DTCs). DTCs identify the
system faults to aid the technician in making repairs.

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2

TRANSMISSION CONTROL SYSTEM (JR405E)   7A2-153

TCM Input & Output 

TCM Voltage Description

The TCM supplies a buffered voltage to various
switches and sensors. The TCM can do this because
resistance in the TCM is so high in value that a test
lamp may not illuminate when connected to the circuit.
An ordinary shop voltmeter may not give an accurate
reading because the voltmeter input impedance is too
low. Use a 10-megaohm input impedance DMM, to
ensure accurate voltage readings. The input and/ or
output devices in the TCM include analog-to-digital
converters, signal buffers, counters, and special
drivers. The TCM controls most components with
electronic switches which complete a ground circuit
when turned ON.

Electrostatic Discharge Damage

Electronic components used in the TCM are often
designed to carry very low voltage. Electronic
components are susceptible to damage caused by
electrostatic discharge. By comparison, as much as
4,000 volts may be needed for a person to feel even
the zap of a static discharge. There are several ways
for a person to become statically charged. The most
common methods of charging are by friction and
induction.

• An example of charging by friction is a person

sliding across a vehicle seat.

Important: To prevent possible electrostatic discharge
damage, follow these guidelines:

• Do not touch the TCM connector pins or soldered

components on the TCM circuit board. 

• Do not open the replacement part package until

the part is ready to be installed. 

• Before removing the part from the package,

ground the package to a known good ground on
the vehicle.

• If the part has been handled while sliding across

the seat, while sitting down from a standing
position, or while walking a distance, touch a
known good ground before installing the part.

• Charge by induction occurs when a person with

well insulated shoes stands near a highly charged
object and momentarily touches ground. Charges
of the same polarity are drained off leaving the
person highly charged with opposite polarity.

Sensor inputs

Input shaft speed (ISS) sensor

Output shaft speed (OSS) sensor

Transmission fluid temperature (TFT) sensor

Accelerator pedal position signal (via ECM)

Engine speed signal (via ECM)

Switch inputs

Low & reverse brake transmission fulid
pressure (TFP) switch 

2-4 brake transmission fulid pressure (TFP)
switch 

High clutch transmission fulid pressure (TFP) 
switch

Transmission range (TR) switch 

Power drive switch

3rd start switch

Brake pedal switch

4WD low gear signal (via TCCM)

TCM

Solenoid valve outputs

Pressure control (PC) solenoid valve

Torque converter clutch (TCC) solenoid valve

Low & reverse brake solenoid valve  

2-4 brake solenoid valve 

High clutch solenoid valve 

Low clutch solenoid valve 

Other outputs

Vehicle speed signal (2WD only)

Communication

Scan tool

Lamp control outputs

Check trans lamp

A/T oil temp. lamp

Power drive lamp  

3rd start lamp  

7A2-154   TRANSMISSION CONTROL SYSTEM (JR405E)

Check Trans Lamp Operation

The check trans lamp is located in the instrument panel
cluster. 

The check trans lamp indicates that a transmission
related fault has occurred and vehicle service is
required. The following is a list of the modes of
operation for the check trans lamp:

• The check trans lamp illuminates for approximately

3 seconds when the ignition switch is turned ON,
with the engine OFF. This is a bulb test to the
check trans lamp is able to illuminate.

• The check trans lamp turns OFF after the engine is

started if a diagnostic fault is not present.

• The check trans lamp remains blink after the

engine is started if the TCM detects a fault. A DTC
is stored any time the TCM blinks the check trans
lamp due to a transmission related fault has
occurred. 

Line Pressure Control 

Solenoid valve outputs

Pressure control (PC) solenoid valve 

Switch inputs

Transmission range (TR) switch

Sensor inputs

Input shaft speed (ISS) sensor
Output shaft speed (OSS) sensor
Accelerator pedal position signal (via ECM)
Engine speed signal (via ECM)

TCM

TRANSMISSION CONTROL SYSTEM (JR405E)   7A2-155

Legend

1. PC solenoid valve
2. Pressure regulator spool valve
3. Spring
4. Line pressure from oil pump
5. Solenoid fluid pressure
6. Line pressure in forward range 

7. Adjusted line pressure
8. Drain 
9. PC solenoid valve commanded ON

10. PC solenoid valve commanded OFF

11. Adjusted line pressure in P, N or R range 

12. Adjusted line pressure in forward range 

The TCM drives the ON/ OFF type pressure control
(PC) solenoid valve based on the accelerator pedal
angle, input shaft speed, output shaft speed,
transmission fluid temperature and transmission range
signal. 
The line pressure generated by the oil pump acts on
the point A of the pressure regulator spool valve. When
the PC solenoid valve is turned ON by the signal from
the TCM, the solenoid fluid pressure does not act. The
line pressure is adjusted to match the spring force
acting on the right side of the pressure regulator spool
valve. When the PC solenoid valve is turned OFF, the
solenoid fluid pressure acts so that the line pressure is
adjusted to match the spring force acting on the right
side of the pressure regulator spool valve. As a result,
the line pressure is adjusted to be low when the PC
solenoid valve is ON and to be high when the PC
solenoid valve is OFF. In position D, 3, 2 and L, the line
pressure through the oil pressure circuit acts onto the
point B of the pressure regulator spool valve. The
pressure regulator valve moves so as to increase the
pressure to be drained, so that the line pressure is
adjusted to be lower than the P, N, and R position by
the difference of area at the point B.

11

7

12

4

6

B

A

2

7

8

3

1

5

9

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