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

