Isuzu KB P190. Manual — part 303

6E-178 Engine Control System (4JH1)

Step Action

Value(s)

Yes

No

15

Important: Replacement ECM must be
programmed.
Replace the ECM. Refer to Engine Control Module
(ECM) Replacement in this section.
Did you complete the replacement?



Go to Step 16



16 1. Reconnect all previously disconnected fuse,

relay or harness connector(s).

2. Clear the DTCs with the scan tool.
3. Turn OFF the ignition for 30 seconds.
4. Turn ON the ignition, with the engine OFF.
5. Turn ON the blower motor switch and the A/C

compressor switch.

6. Turn OFF the A/C compressor switch.
7. Monitor the DTC Information with the scan tool.
Does the DTC fail this ignition?



Go to Step 3

Go to Step 17

17

Observe the DTC Information with the scan tool.
Are there any DTCs that you have not diagnosed?



Go to Diagnostic

Trouble Code (DTC)

List System

OK

Engine Control System (4JH1) 6E-179

DTC P0645 (Symptom Code 8) (Flash Code 46)

Circuit Description
The engine control module (ECM) controls the air
conditioning (A/C) compressor relay, which supplies
power to the A/C compressor clutch based on A/C
request input to the ECM from the heating, ventilation
and air conditioning (HVAC) controls. The ECM
commands the A/C compressor relay ON at engine run.
If the ECM detects a short to battery or ignition voltage
on the A/C compressor relay control circuit, this DTC
will set.
Condition for Running the DTC

• The ignition switch is ON.

• The A/C compressor relay is once commanded

ON.

Condition for Setting the DTC

• The ECM detects a high voltage condition on the

A/C compressor relay control circuit for longer than
3 seconds when the relay is commanded ON.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

Condition for Clearing the MIL/DTC

• The ECM turns OFF the MIL when the diagnostic

runs and does not fail.

• A history DTC clears after 40 consecutive driving

cycles without a fault. Or clear with the scan tool.

Diagnostic Aids

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

Notice:

• The A/C compressor relay is commanded OFF

when the engine coolant temperature is reached
around 105°C (221°F) and it commanded ON
again below 100°C (212°F).

DTC P0645 (Symptom Code 8) (Flash Code 46)
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views or Engine Control Module (ECM)
Connector End Views

Step Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check-
Engine Controls?



Go to Step 2

Go to Diagnostic

System Check-

Engine Controls

2

1. Install the scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Turn ON the blower motor switch and the A/C

compressor switch.

5. Monitor the Diagnostic Trouble Code (DTC)

Information with the scan tool when the A/C
Relay Command parameter is ON.

Does the DTC fail this ignition?



Go to Step 3

Go to Diagnostic

Aids

3

1. Turn OFF the ignition.
2. Replace the A/C compressor relay with the tail

relay or replace with a known good relay.

3. Start the engine.
4. Turn ON the blower motor switch and the A/C

compressor switch.

5. Monitor the DTC Information with the scan tool

when the A/C Relay Command parameter is ON.

Does the DTC fail this ignition?



Go to Step 4

Go to Step 5

4

1. Test the control circuit of the A/C compressor

relay between the ECM (pin 41 of C-56
connector) and the A/C compressor relay (pin 5
of X-14 connector) 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 7

Go to Step 6

5

Replace the A/C compressor relay.
Did you complete the replacement?



Go to Step 7



6E-180 Engine Control System (4JH1)

Step Action

Value(s)

Yes

No

6

Important: Replacement ECM must be
programmed.
Replace the ECM. Refer to Engine Control Module
(ECM) Replacement in this section.
Did you complete the replacement?



Go to Step 7



7

1. Reconnect all previously disconnected relay or

harness connector(s).

2. Clear the DTCs with the scan tool.
3. Turn OFF the ignition for 30 seconds.
4. Start the engine.
5. Turn ON the blower motor switch and the A/C

compressor switch.

6. Monitor the DTC Information with the scan tool

when the A/C Relay Command parameter is ON.

Did the DTC fail this ignition?



Go to Step 3

Go to Step 8

8

Observe the DTC Information with the scan tool.
Are there any DTCs that you have not diagnosed?



Go to Diagnostic

Trouble Code (DTC)

List System

OK

Engine Control System (4JH1) 6E-181

DTC P0703 (Symptom Code A, B) (Flash Code 25)

Circuit Description
The brake pedal switch is installed on the brake pedal
bracket. The brake pedal 1 switch is a normally open
type switch and the brake pedal 2 switch is a normally
closed type switch. When the brake pedal is pressed,
the brake pedal 1 switch signal is provided to the engine
control module (ECM) and the stoplights are turned ON.
Then, the brake pedal 2 switch signal to the ECM is
stopped (low voltage). If the ECM detects the brake
switch signals out of correlation, this DTC will set.
Condition for Running the DTC

• The ignition switch is ON.
• The engine speed is higher than 665 RPM.
• The vehicle speed is higher than 0 km/h (0 MPH).

Condition for Setting the DTC

• The ECM detects that the brake pedal 1 switch

(normally open type switch) signal and brake pedal
2 switch (normally closed type switch) signal
correlation error for longer than 30 seconds within
the enabling conditions ever since ignition switch is
ON. (Symptom Code A)

• The ECM detects that the brake pedal 1 switch

(normally open type switch) signal and brake pedal
2 switch (normally closed type switch) signal
correlation error for longer than 30 seconds.
(Symptom Code B)

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

Condition for Clearing the MIL/DTC

• The ECM turns OFF the MIL when the diagnostic

runs and does not fail.

• A history DTC clears after 40 consecutive driving

cycles without a fault. Or clear with the scan tool

Diagnostic Aids

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

• Misadjusted brake pedal switch will cause this

DTC to set.

DTC P0703 (Symptom Code A, B) (Flash Code 25)
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views or Engine Control Module (ECM)
Connector End Views

Step Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check-
Engine Controls?



Go to Step 2

Go to Diagnostic

System Check-

Engine Controls

2

1. Install the scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Observe the Brake Pedal 1 Switch parameter

with the scan tool while fully depressing and
releasing the brake pedal.

Does the scan tool indicate Applied when the brake
pedal is applied and Released when the brake pedal
is released?



Go to Step 10

Go to Step 3

3

1. Check to ensure the brake pedal switch is

adjusted correctly. The plunger should be all the
way in when the pedal is released, yet should not
impede with the brake pedal full upward travel.

2. Adjust the brake pedal switch as necessary.
Did you find and correct the condition?



Go to Step 22

Go to Step 4

4

1. Turn OFF the ignition.
2. Inspect the Stop (15A) fuse (C-15) in the cabin

fuse block.

Is the Stop (15A) fuse (C-15) open?



Go to Step 5

Go to Step 6