Isuzu N-Series. Service manual - part 774

 

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Isuzu N-Series. Service manual - part 774

 

 

 Engine Control System (4JH1)    6E-147

P0645 (Symptom Code 4) (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 an open circuit or short to
ground 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 low voltage condition on the A/

C compressor relay control circuit for longer than 3
seconds when the relay is commanded OFF.

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 Tech 2.

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 115

°C (239°F) and it commanded ON

again below 110

°C (230°F).

DTC P0645 (Symptom Code 4) (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 Tech 2.

2.

Turn OFF the ignition for 30 seconds.

3.

Start the engine and let idle.

4.

Turn ON the blower motor switch and the A/C
compressor switch.

5.

Turn OFF the A/C compressor switch.

6.

Monitor the Diagnostic Trouble Code (DTC)
Information with the Tech 2.

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
marker light relay or replace with a known
good relay.

3.

Start the engine and let idle.

4.

Turn ON the blower motor switch and the A/C
compressor switch.

5.

Turn OFF the A/C compressor switch.

6.

Monitor the DTC Information with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 4

Go to Step 12

6E-148    Engine Control System (4JH1) 

4

1.

Turn OFF the ignition.

2.

Remove the A/C compressor relay.

3.

Connect a test lamp between the voltage feed
circuit of the A/C compressor relay coil side
(pin 4 of X-24 connector) and a known good
ground.

4.

Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

—

Go to Step 5

Go to Step 7

5

1.

Turn OFF the ignition.

2.

Connect a test lamp between the A/C
compressor relay control circuit (pin 2 of X-24
connector) and battery voltage.

3.

Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

—

Go to Step 8

Go to Step 6

6

1.

Keep the test lamp with connected.

2.

Start the engine.

3.

Turn ON the blower motor switch and the A/C
compressor switch.

Does the test lamp illuminate when the A/C
Compressor Relay parameter is ON?

—

Go to Step 10

Go to Step 9

7

Repair the open circuit or high resistance on the
voltage feed circuit between the ECM main relay
(pin 5 of X-14 connector) and the A/C compressor
relay (pin 4 of X-24 connector).

Did you complete the repair?

—

Go to Step 14

—

8

1.

Test the control circuit of the A/C compressor
relay between the ECM (pin 41 of B-234
connector) and the A/C compressor relay (pin
2 of X-24 connector) for a short to ground.

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 14

Go to Step 13

9

1.

Test the control circuit of the A/C compressor
relay between the engine control module
(ECM) (pin 41 of B-234 connector) and the A/
C compressor relay (pin 2 of X-24 connector)
for an open circuit or high resistance.

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 14

Go to Step 11

10

1.

Turn OFF the ignition.

2.

Inspect for an intermittent and for poor
connections on the A/C compressor relay
terminal (pins 2 and 4 of X-24 connector).

3.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 14

Go to Step 12

11

1.

Turn OFF the ignition.

2.

Disconnect the ECM harness connector.

3.

Inspect for an intermittent and for a poor
connection on the A/C compressor relay
control circuit at the harness connector of the
ECM (pin 41 of B-234 connector).

4.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 14

Go to Step 13

Step

Action

Value(s)

Yes

No

 Engine Control System (4JH1)    6E-149

12

Replace the A/C compressor relay.

Did you complete the replacement?

—

Go to Step 14

—

13

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 14

—

14

1.

Reconnect all previously disconnected fuse,
relay or harness connector(s).

2.

Clear the DTCs with the Tech 2.

3.

Turn OFF the ignition for 30 seconds.

4.

Start the engine and let idle.

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 Tech 2.

Does the DTC fail this ignition?

—

Go to Step 3

Go to Step 15

15

Observe the DTC Information with the Tech 2.

Are there any DTCs that you have not diagnosed?

—

Go to Diagnostic 

Trouble Code (DTC) 

List

System OK

Step

Action

Value(s)

Yes

No

6E-150    Engine Control System (4JH1) 

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 Tech 2.

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 115

°C (239°F) and it commanded ON

again below 110

°C (230°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 Tech 2.

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 Tech 2 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
marker light 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 Tech 2
when the A/C Relay Command parameter is
ON.

Does the DTC fail this ignition?

—

Go to Step 4

Go to Step 5

 

 

 

 

 

 

 

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