Isuzu 4ja1, Workshop Manual

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Engine Control System (4JH1) 6E-163
DTC 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 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 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 scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Turn ON the ignition, with the engine OFF.
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 scan tool.
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. Turn ON the ignition, with the engine OFF.
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 scan tool.
Does the DTC fail this ignition?

Go to Step 4 Go to Step 14
4 1. Turn OFF the ignition.
2. Inspect the ECM (10A) fuse (EB-4) in the engine
room fuse block.
Is the ECM (10A) fuse (EB-4) open?

Go to Step 5 Go to Step 6
5 Replace the ECM (10A) fuse (EB-4). If the fuse
continues to open, repair the short to ground on one
of the circuits that is fed by the ECM (10A) fuse (EB-
4) or replace the shorted attached component fed by
the ECM (10A) fuse (EB-4).
Did you complete the repair?

Go to Step 16
