Isuzu KB P190. Manual - part 1088

7A2-68   TRANSMISSION CONTROL SYSTEM (JR405E)

4

1.

Turn OFF the ignition. 

2.

Disconnect the in-line harness connector (E-
54) near the transmission range switch.

3.

Connect a test lamp between the control
circuit (pin 3 of E-54 female side) and a known
good ground. 

4.

Turn ON the ignition, with the engine OFF. 

5.

Perform the Low Clutch Solenoid control with
a scan tool.

6.

Command the solenoid valve ON and OFF.

Does the test lamp turn ON and OFF with each
command?

—

Go to Step 9

Go to Step 5

5

Does the test lamp remain illuminated with each
command?

—

Go to Step 6

Go to Step 7

6

1.

Test the control circuit between the TCM (pin 9
of C-95) and the in-line harness connector (pin
3 of E-54 female side) for a short to battery or
ignition voltage. 

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 12

7

1.

Test the control circuit between the TCM (pin 9
of C-95) and the in-line harness connector (pin
3 of E-54 female side) for the following
conditions:

• An open circuit

• A short to ground

• High resistance 

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 8

8

1.

Turn OFF the ignition. 

2.

Disconnect the TCM harness connector.

3.

Inspect for an intermittent and for a poor
connection at the harness connector of the
TCM (pin 9 of C-95). 

4.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 12

9

1.

Inspect for an intermittent and for a poor
connection at the in-line harness connector
(pin 3 of E-54).

2.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 10

Step

Action

Value(s)

Yes

No

TRANSMISSION CONTROL SYSTEM (JR405E)   7A2-69

10

1.

Remove the transmission oil pan. Refer to
repair instructions (On-Vehicle Service). 

2.

Inspect the low clutch solenoid valve for the
following conditions:

• Physical damage of solenoid valve 

• Loose or improper installation of solenoid

valve

3.

Inspect for an intermittent and for a poor
connection at the harness connector of the
low clutch solenoid valve or in-line harness
connector. 

4.

Inspect for an intermittent and for a poor
connection of ground wire.   

5.

Test the control circuit between the low clutch
solenoid valve and the in-line harness
connector (pin 3 of E-54 male side) for the
following conditions:

• An open circuit

• A short to ground

• A short to the other solenoid valve circuit

• High resistance 

6.

Repair the connection(s) or circuit(s) as
necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 11

11

Replace the low clutch solenoid valve. Refer to
repair instructions (On-Vehicle Service). 

Did you complete the replacement?

—

Go to Step 13

—

12

Important: Replacement TCM must be
programmed.
Replace the TCM. Refer to TCM Replacement.

Did you complete the replacement?

—

Go to Step 13

—

13

1.

Reconnect all previously disconnected
components or harness connector(s).

2.

Clear the DTCs with a scan tool.

3.

Turn OFF the ignition for 30 seconds. 

4.

Start the engine.

5.

Lift the driving wheels or drive the vehicle
while observing the DTC Information with a
scan tool. 

Did the DTC fail this ignition?

—

Go to Step 4

Go to Step 14

14

Observe the DTC Information with a scan tool.

Are there any DTCs that you have not diagnosed?

—

Go to DTC List 

System OK

Step

Action

Value(s)

Yes

No

7A2-70   TRANSMISSION CONTROL SYSTEM (JR405E)

DTC P1120 (Flash Code 22)

Circuit Description

The accelerator pedal position (APP) sensor is
mounted on the accelerator pedal control assembly.
The analogue APP signals are converted by the engine
control module (ECM) into a pulse width modulation
(PWM) signal. This converted signal is continually sent
from the ECM to the TCM to determine appropriate
shift points depending on the accelerator pedal
pressing amount. If the TCM fails to receive a PWM
signal from the ECM, this DTC will set.

Condition for Running the DTC

• The ignition switch is ON. 

Condition for Setting the DTC

• The TCM detects that the APP PWM signal from

the ECM is not being received. 

Action Taken When the DTC Sets

• The TCM blinks the Check Trans lamp when the

diagnostic runs and fails.

During the vehicle running;

• The TCM holds the last gear position when the

diagnostic runs and fails.

• The TCM inhibits lock up control.

After the vehicle stopped;

• The TCM stops all shift solenoid valves and fixes

to the 3rd gear. If a fail-safe valve problem is
detected, the shift solenoid valves are not stopped
but gear is fixed to the 3rd gear. 

• The TCM stops PC solenoid valve.

Condition for Clearing the DTC

• The TCM turns OFF the Check Trans lamp when

the diagnostic runs and does not fail.

• A current DTC clears when the diagnostic runs and

does not fail. 

Diagnostic Aids

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

Circuit/ System Testing DTC P1120

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check -
Transmission Controls?

—

Go to Step 2

Go to Diagnostic 

System Check - 

Transmission 

Controls

2

1.

Install a scan tool.

2.

Turn OFF the ignition for 30 seconds.

3.

Start the engine.

4.

Monitor the ENGINE DTC Information with a
scan tool.

Is DTC P2621 or P2622 set?

—

Go to Applicable 

DTC in engine 
control section

Go to Diagnostic 

Aids

TRANSMISSION CONTROL SYSTEM (JR405E)   7A2-71

DTC P1750 (Flash Code 51)

Circuit Description

The low & reverse brake transmission fluid pressure
(TFP) switch is installed to the lower part of the valve
body assembly and it feedbacks fluid pressure in the
low & reverse brake hydraulic circuit. The low & reverse
brake fail-safe spool valves are installed to the control
valve body assembly and it uses to prevent interlocking
of clutches and brakes. When the solenoid valve is
energized, fluid pressure is drained to disengage the
low & reverse brake and the TFP switch is OFF. When
the solenoid valve is not energized, fluid pressure is
applied to engage the low & reverse brake and the TFP
switch is ON. The TCM monitors the low & reverse
brake TFP switch ON/ OFF status through the signal
circuit. If the TCM detects an improper status on the
signal circuit, this DTC will set. 

Condition for Running the DTC

• The ignition switch is ON. 

Condition for Setting the DTC

• The TCM detects that the low & reverse brake TFP

switch signal repeats OFF/ ON twice when the
selector lever in forward range with the 2nd, 3rd or
4th gear. 

Action Taken When the DTC Sets

• The TCM blinks the Check Trans lamp when the

diagnostic runs and fails.

During the vehicle running;

• The TCM holds the last gear position when the

diagnostic runs and fails.

• The TCM inhibits lock up control.

After the vehicle stopped;

• The TCM fixes to the 3rd gear. 

Condition for Clearing the DTC

• The TCM turns OFF the Check Trans lamp when

the diagnostic runs and does not fail at next
ignition cycle.

• A current DTC clears when the diagnostic runs and

does not fail at next ignition cycle.

Diagnostic Aids

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

• Use the Clutch, Brake, Solenoid and Pressure

Switch Logic table to verify each component works
properly within the selected gear range.

• A sticking or intermittently sticking the low &

reverse brake solenoid valve will cause this DTC to
set.

Schematic Reference: Transmission Controls
Schematics
Connector End View Reference: Transmission
Controls Connector End Views or TCM Connector End
Views

Circuit/ System Testing DTC P1750

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check -
Transmission Controls?

—

Go to Step 2

Go to Diagnostic 

System Check -

Transmission 

Controls

2

1.

Install a scan tool. 

2.

Turn OFF the ignition for 30 seconds. 

3.

Lift the driving wheels or drive the vehicle
while observing the DTC Information with a
scan tool.

Is DTC P0753 or P1853 also set?

—

Go to Applicable 

DTC

Go to Step 3

3

Place the selector lever in forward range while
observing the Low & Reverse Brake Pressure
Switch parameter with a scan tool.

Does the Low & Reverse Brake Pressure Switch
parameter ever indicate ON when gear is shifted
between 1st and 4th?

—

Go to Step 4 

Go to Diagnostic 

Aids