Isuzu KB P190. Manual - part 321

6E-250  Engine Control System (4JH1) 

Step Action 

Value(s) 

Yes 

No 

7 

Repair the short to ground between the pressure 
switch (pin 2 of C-24 connector) and the electronic 
thermostat (pin 2 of C-55 connector). 
Did you complete the repair? 

 

Go to Step 43 

 

8 

1.  Test the electronic thermostat switching circuits 

shorted each other. (pins 1 and 2 of C-55 
connector). 

2.  Repair the circuits as necessary. 
Did you find and correct the condition? 

 

Go to Step 43 

Go to Step 39 

9 

1.  Test the electronic thermostat circuit between the 

electronic thermostat (pin 4 of C-55 connector) 
and the A/C switch (pin 11 of B-57 connector) for 
a short to ground. 

2.  Repair the circuits as necessary. 
Did you find and correct the condition? 

 

Go to Step 43 

Go to Step 40 

10 

1. Test the ground circuit among the electronic 

thermostat (pin 1 of C-55 connector), the blower 
motor switch (pin 1 of B-13 connector) and the 
A/C switch (pin 10 of B-57 connector) for a short 
to ground. 

2.  Repair the circuits as necessary. 
Did you find and correct the condition? 

 

Go to Step 43 

Go to Step 41 

11 

Inspect the A/C (10A) fuse (EB-13) in the engine 
room fuse block. 
Is the A/C (10A) fuse (EB-13) open? 

 

Go to Step 12 

Go to Step 13 

12 

1.  Replace the A/C (10A) fuse (EB-13). If the fuse 

continues to open, repair the short to ground on 
a circuit fed by the fuse or check for a shorted 
attached component. 

2. Repair the short to ground or replace the 

component as necessary. 

Did you complete the repair? 

 

Go to Step 43 

 

13 

1.  Turn OFF the ignition. 
2.  Remove the thermo relay from the engine room 

relay block. 

3.  Connect a test lamp between the voltage feed 

circuit (pins 2 and 3 of X-15 connector) and a 
known good ground. 

4.  Turn ON the ignition, with the engine OFF. 
Does the test lamp illuminate on both circuits?  

 

Go to Step 14 

Go to Step 23 

14 

1.  Turn OFF the ignition. 
2.  Reinstall the thermo relay. 
3.  Remove the radiator grille in order to access the 

pressure switch. 

4. 

Disconnect the pressure switch harness 
connector (C-24). 

5.  Connect a 3-amp fused jumper wire between the 

pressure switch harness (pin 1 of C-24 
connector) and a known good ground. 

6.  Turn ON the ignition, with the engine OFF. 
Does the thermo relay click (engage)? 

 

Go to Step 15 

Go to Step 17 

15 

Does the A/C Clutch Switch parameter indicate ON?

 

Go to Step 18 

Go to Step 16 

Engine Control System (4JH1)  6E-251 

Step Action 

Value(s) 

Yes 

No 

16 

1.  Turn OFF the ignition. 
2.  Keep the 3-amp fused wire with connected. 
3.  Disconnect the ECM C-56 harness connector. 
4.  Connect a test lamp between the thermo relay 

input circuit (pin 33 of C-56 connector) and a 
known good ground. 

5.  Turn ON the ignition, with the engine OFF. DO 

NOT START the engine. 

Does the test lamp illuminate? 

 

Go to Step 36 

Go to Step 24  

17 

1.  Turn OFF the ignition. 
2.  Keep the 3-amp fused wire with connected. 
3.  Replace the thermo relay with the horn relay or 

replace with a known good relay. 

4.  Connect a 3-amp fused jumper wire between the 

pressure switch harness (pin 1 of C-24 
connector) and a known good ground. 

5.  Turn ON the ignition, with the engine OFF. 
Does the thermo relay click (engage)? 

 

Go to Step 31 

Go to Step 25 

18 

1.  Turn OFF the ignition. 
2.  Connect the pressure switch harness connector. 
3. Remove the grove box in order to access 

electronic thermostat. 

4. Disconnect the electronic thermostat harness 

connector (C-55). 

5.  Connect a 3-amp fused jumper wire between the 

electronic thermostat voltage feed circuit (pin 2 of 
C-55 connector) and a known good ground. 

6.  Turn ON the ignition, with the engine OFF. 
Does the thermo relay click (engage)? 

 

Go to Step 19  

Go to Step 26 

19 

1.  Turn OFF the ignition. 
2. Connect a test lamp between the electronic 

thermostat terminal (pin 1 of C-55 connector) and 
battery voltage. 

3.  Turn ON the blower motor switch. 
Does the test lamp illuminate? 

 

Go to Step 20 

Go to Step 27 

20 

1.  Turn OFF the ignition. 
2. Connect a test lamp between the electronic 

thermostat voltage feed circuit (pin 3 of C-55 
connector) and a known good ground. 

3.  Turn ON the ignition, with the engine OFF. 
Does the test lamp illuminate? 

 

Go to Step 21 

Go to Step 28 

21 

1.  Turn OFF the ignition. 
2. Connect a test lamp between the electronic 

thermostat terminal (pin 4 of C-55 connector) and 
battery voltage. 

3.  Turn ON the blower motor switch. 
4.  Turn ON the A/C switch. 
Does the test lamp illuminate? 

 

Go to Step 33 

Go to Step 22 

6E-252  Engine Control System (4JH1) 

Step Action 

Value(s) 

Yes 

No 

22 

1.  Turn OFF the ignition. 
2. Remove the center cluster bezel in order to 

remove HVAC control lever. 

3.  Disconnect the A/C switch harness connector (B-

57). 

4.  Connect a test lamp between the A/C switch 

ground harness (pin 10 of B-57 connector) and 
battery voltage. 

5.  Turn ON the blower motor switch. 
Does the test lamp illuminate? 

 

Go to Step 29 

Go to Step 30 

23 

Repair the open circuit or high resistance on the 
thermo relay voltage feed circuits between the 
thermo relay (pin 2 of X-15 connector) and ECM 
(10A) fuse (EB-4), then thermo relay (pin 3 of X-15 
connector) and A/C (10A) fuse (EB-13). 
Did you complete the repair? 

 

Go to Step 43 

 

24 

Repair the open circuit or high resistance on thermo 
relay input circuit between the ECM (pin 33 of C-56 
connector) and the thermo relay (pin 1 of X-15 
connector). 
Did you complete the repair? 

 

Go to Step 43 

 

25 

Repair the open circuit or high resistance on the 
pressure switch voltage feed circuit between the 
thermo relay (pin 5 of X-15 connector) and pressure 
switch (pin 1 of C-24) connector. 
Did you complete the repair? 

 

Go to Step 43 

 

26  1. Test the voltage feed circuit between the 

pressure switch (pin 2 of C-24 harness 
connector) and electronic thermostat (pin 2 of C-
55 connector) for an open or high resistance. 

2.  Repair the circuit as necessary. 
Did you find and correct the condition? 

 

Go to Step 43 

Go to Step 32 

27 

1.  Test the electronic thermostat switching circuit 

between the electronic thermostat (pin 1 of C-55 
connector) and the blower motor switch (pin 1 of 
B-13 connector) for an open or high resistance. 

2.  Repair the circuit as necessary. 
Did you find and correct the condition? 

 

Go to Step 43 

Go to Step 35 

28 

Repair the open or high resistance on the voltage 
feed circuit on the electronic thermostat between the 
A/C (10A) fuse (EB-13) and the electronic 
thermostat (pin 3 of C-55 connector). 
Did you complete the repair? 

 

Go to Step 43 

 

29 

1.  Test the electronic thermostat circuit between the 

electronic thermostat (pin 4 of C-55 connector) 
and A/C switch (pin 11 of B-57 connector) for an 
open or high resistance. 

2.  Repair the circuit as necessary. 
Did you find and correct the condition? 

 

Go to Step 43 

Go to Step 34 

30 

1.  Test the A/C switch ground circuit between the 

A/C switch (pin 10 of B-57 connector) and blower 
motor switch (pin 1 of B-13 connector) for an 
open or high resistance. 

2.  Repair the circuit as necessary. 
Did you find and correct the condition? 

 

Go to Step 43 

Go to Step 35 

Engine Control System (4JH1)  6E-253 

Step Action 

Value(s) 

Yes 

No 

31 

1.  Turn OFF the ignition. 
2. Inspect for an intermittent and for poor 

connections at the thermo relay terminals (pins 
1, 2, 3 and 4 of X-15 connector). 

3.  Repair the connection(s) as necessary. 
Did you find and correct the condition? 

 

Go to Step 43 

Go to Step 37 

32 

1.  Turn OFF the ignition. 
2. Inspect for an intermittent and for poor 

connections at the harness connector of the 
pressure switch (pins 1 and 2 of C-24 connector).

3.  Repair the connection(s) as necessary. 
Did you find and correct the condition? 

 

Go to Step 43 

Go to Step 38 

33 

1.  Turn OFF the ignition. 
2. Inspect for an intermittent and for poor 

connections at the harness connector of the 
electronic thermostat (pins 1, 2, 3 and 4 of C-55 
connector). 

3.  Repair the connection(s) as necessary. 
Did you find and correct the condition? 

 

Go to Step 43 

Go to Step 39 

34 

1.  Turn OFF the ignition. 
2. Inspect for an intermittent and for poor 

connections at the harness connector of the A/C 
switch (pins 10 and 11 of B-57 connector). 

3.  Repair the connection(s) as necessary. 
Did you find and correct the condition? 

 

Go to Step 43 

Go to Step 40 

35 

1.  Turn OFF the ignition. 
2. Inspect for an intermittent and for a poor 

connection at the harness connector of the 
blower motor switch (pin 1 of B-13 connector). 

3.  Repair the connection(s) as necessary. 
Did you find and correct the condition? 

 

Go to Step 43 

 Go to Step 41 

36 

1.  Turn OFF the ignition. 
2. Inspect for an intermittent and for a poor 

connection at the harness connector of the ECM 
(pin 33 of C-56 connector). 

3.  Repair the connection(s) as necessary. 
Did you find and correct the condition? 

 

Go to Step 43 

Go to Step 42 

37 

Replace the thermo relay. 
Did you complete the replacement? 

 

Go to Step 43 

 

38 

Replace the pressure switch. Refer to Heating and 
Air Conditioning section. 
Did you complete the replacement? 

 

Go to Step 43 

 

39 

Replace the electronic thermostat. Refer to Heating 
and Air Conditioning section. 
Did you complete the replacement? 

 

Go to Step 43 

 

40 

Replace the A/C switch. Refer to Heating and Air 
Conditioning section. 
Did you complete the replacement? 

 

Go to Step 43 

 

41 

Replace the blower motor switch. Refer to Heating 
and Air Conditioning section. 
Did you complete the replacement? 

 

Go to Step 43 

 

42 

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 43 

