Isuzu 4JA1 Workshop Manual page 472

6E-218 Engine Control System (4JH1)
DTC P1651 (Symptom Code A, B) (Flash Code 45)
Circuit Description
The engine control module (ECM) calculates the
desired fuel injection quantity and timing using data sent
from various sensors. These desired data are sent to
the fuel injection pump control unit (PCU) via a
controller area network (CAN) communication bus. The
PCU also receives signals from the internal inputs:
pump camshaft position (CMP) sensor that is located
inside the fuel injection pump to determine the cam ring
rotation angle and the fuel injection pump speed. The
fuel temperature (FT) sensor is internal the PCU. These
values are used to compare the desired values sent
from the ECM then PCU determines the injection timer
piston position and fuel injection quantity, and actuates
timing control valve (TCV) & fuel injection solenoid
valve based on control maps in the PCU.
The ECM monitors CAN operational status by expecting
a constant flow of messages from the PCU. If the ECM
fails to receive an expected message from the PCU,
this will set depending on what communication is lost.
Condition for Setting the DTC
• The ECM detects that the PCU does not receive
the CAN messages from the ECM. (Symptom
Code A)
Step
1 Did you perform the Diagnostic System Check-
Engine Controls?
2 1. Install the scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Monitor the Diagnostic Trouble Code (DTC)
Information with the scan tool.
Does the DTC fail this ignition?
3 1. Turn OFF the ignition.
2. Disconnect the fuel injection pump control unit
(PCU) harness connector.
3. Connect a DMM across the controller area
network (CAN) harness (pins 1 and 2 of E-6
connector).
4. Measure the
terminals.
Is the resistance within the specified value?
4 1. Connect a DMM between the CAN Low signal
circuit (pin 1 of E-6 connector) and a known good
ground.
2. Turn ON the ignition, with the engine OFF.
Is the DMM voltage within the specified value?
5 1. Keep the ignition switch ON, with the engine
OFF.
2. Connect a DMM between the CAN High signal
circuit (pin 2 of E-6 connector) and a known good
ground.
Is the DMM voltage within the specified value?
Action
resistance across the
• The ECM does not receive the CAN messages
from the PCU. (Symptom Code B)
Action Taken When the DTC Sets
• The ECM illuminates the malfunction indicator
lamp (MIL) when the diagnostic runs and fails.
The ECM cuts the fuel injection.
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.
DTC P1651 (Symptom Code A, B) (Flash Code 45)
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views or Engine Control Module (ECM)
Connector End Views
Value(s)


110-130Ω
CAN
1.5 – 2.5 volts
3.0 – 4.0 volts
Yes
Go to Diagnostic
System Check-
Go to Step 2 Engine Controls
Go to Step 3 Go to Step 4
Go to Step 4 Go to Step 9
Go to Step 5 Go to Step 10
Go to Step 6 Go to Step 11
No