Isuzu KB P190. Manual - part 1089

7A2-72   TRANSMISSION CONTROL SYSTEM (JR405E)

4

1.

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

2.

Inspect the low & reverse brake solenoid valve
and transmission fluid pressure (TFP) switch
for the following conditions:

• Physical damage

• Loose or improper installation 

3.

Test the signal circuit between the low &
reverse brake TFP switch and the in-line
harness connector (pin 12 of E-54 male side)
for a short to ground.

4.

Repair the circuit(s) or replace as necessary. 

Did you find and correct the condition?

—

Go to Step 7

Go to Step 5

5

1.

Remove the low & reverse brake solenoid
valve and TFP switch from the valve body
assembly and perform function check. Refer
to repair instructions (On-Vehicle Service).

2.

Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 7

Go to Step 6

6

Repair or replace the valve body assembly. Refer
to repair instructions (On-Vehicle Service or Unit
Repair).

Did you complete the repair or replacement?

—

Go to Step 7

—

7

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.

Drive the vehicle while observing the DTC
Information with a scan tool. 

Did the DTC fail this ignition?

—

Go to Step 2

Go to Step 8

8

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

TRANSMISSION CONTROL SYSTEM (JR405E)   7A2-73

DTC P1755 (Flash Code 52)

Circuit Description

The 2-4 brake transmission fluid pressure (TFP) switch
is installed to the lower part of the valve body assembly
and it feedbacks fluid pressure in the 2-4 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 2-4 brake and the
TFP switch is OFF. When the solenoid valve is not
energized, fluid pressure is applied to engage the 2-4
brake and the TFP switch is ON. The TCM monitors the
2-4 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 2-4 brake TFP switch

signal repeats OFF/ ON twice when the selector
lever in forward range with the 3rd 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 2-4 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 P1755

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 P0758or P1858 also set?

—

Go to Applicable 

DTC

Go to Step 3

3

Place the selector lever in forward range while
observing the 2-4 Brake Pressure Switch
parameter with a scan tool.

Does the 2-4 Brake Pressure Switch parameter
ever indicate ON when gear is positioned 1st and
3rd?

—

Go to Step 4 

Go to Diagnostic 

Aids

7A2-74   TRANSMISSION CONTROL SYSTEM (JR405E)

4

1.

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

2.

Inspect the 2-4 brake solenoid valve and
transmission fluid pressure (TFP) switch for
the following conditions:

• Physical damage

• Loose or improper installation 

3.

Test the signal circuit between the 2-4 brake
TFP switch and the in-line harness connector
(pin 7 of E-54 male side) for a short to ground

4.

Repair the circuit(s) or replace as necessary.

Did you find and correct the condition?

—

Go to Step 7

Go to Step 5

5

1.

Remove the 2-4 brake solenoid valve and TFP
switch from the valve body assembly and
perform function check. Refer to repair
instructions (On-Vehicle Service).

2.

Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 7

Go to Step 6

6

Repair or replace the valve body assembly. Refer
to repair instructions (On-Vehicle Service or Unit
Repair).

Did you complete the repair or replacement?

—

Go to Step 7

—

7

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.

Drive the vehicle while observing the DTC
Information with a scan tool. 

Did the DTC fail this ignition?

—

Go to Step 2

Go to Step 8

8

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

TRANSMISSION CONTROL SYSTEM (JR405E)   7A2-75

DTC P1853 (Flash Code 26)

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. 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

• DTCs P0560, P0705, P0717, P0722, P0753,

P0758, P0763, P0768, P1120, P1750, P1755 and
P1875 are not set.

AND following conditions are met for longer than 2.5
seconds.

• The ignition switch is ON.

• The transmission fluid temperature is more than

60

°C (140°F).

• The engine speed is more than 500 RPM. 

• The TCM is not under gearshift control. 

Condition for Setting the DTC

Either of following condition is met:

• The TCM detects that the low & reverse brake TFP

switch signal is stuck at the ON for longer than 2
seconds when the selector lever in D range with
4th gear. 

• The TCM detects that the low & reverse brake TFP

switch signal is stuck at the OFF for longer than 2
second when the selector lever in R range.

Action Taken When the DTC Sets

• The TCM blinks the Check Trans lamp when the

diagnostic runs and fails.

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.

• 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 P1853

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 also set?

—

Go to DTC P0753

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 5 

Go to Step 4