Isuzu 4JA1 Workshop Manual page 487

Step
11 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?
12 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
connector (C-24).
5. Connect a 3-amp fused jumper wire between the
pressure switch
connector) and a known good ground.
6. Turn ON the ignition, with the engine OFF.
Does the thermo relay click (engage)?
13 Does the A/C Request Signal Request parameter
indicate ON?
14 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 30 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?
15 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
connector) and a known good ground.
5. Turn ON the ignition, with the engine OFF.
Does the thermo relay click (engage)?
16 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)?
17 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.
4. Turn ON the A/C switch.
Does the test lamp illuminate?
Action
pressure switch harness
harness (pin 1 of C-24
harness (pin 1 of C-24
Engine Control System (4JH1) 6E-233
Value(s) Yes

Go to Step 12

Go to Step 13

Go to Step 16

Go to Step 32

Go to Step 27

Go to Step 17

Go to Step 18
No
Go to Step 20
Go to Step 15
Go to Step 14
Go to Step 21
Go to Step 22
Go to Step 23
Go to Step 19