Dtc51 - Ecm Internal Fault (Cpu Error / Cpu History Error) - Isuzu 4HL1 Workshop Manual

1A-150 Engine Control System

DTC51 - ECM Internal Fault (CPU Error / CPU History Error)

Circuit Description
The CPU is a processor mounted in the ECM and
receives and processes signals from sensors and
switches to control actuators.
The sub CPU will set DTC51 when the CPU operation
signals are faulty.
Major Faulty Event
• Engine stop
Conditions for Setting the DTC
The sub CPU judges the CPU fail. Otherwise, with the
battery voltage 20 V or more and the starter switch
turned off, the CPU working signals are not detected
even after the initial status lasts for at least 0.4 second.
Action Taken When the DTC Sets
• After the DTC is set, the ECM (sub CPU) will
illuminate the CHECK ENGINE lamp (MIL).
• Upon restoration of CPU, the accelerator position
is limited and then the limitation is relaxed
gradually.
Conditions for Clearing MIL/DTC
When the system fails and the DTC is stored to the
ECM, even repairing the faulty portion will not clear the
DTC from the memory. To clear the DTC, conduct the
following steps.
1. Turn off the idle position switch for not less than 1
second but not more than 3 seconds. (Press the
accelerator pedal.)
2. Turn on the idle position switch for not less than 1
second but not more than 3 seconds. (Release the
accelerator pedal.)
Step
Perform the "On-Board Diagnostic (OBD)
System Check".
1
Was the OBD System Check performed?
Check the ECM connector for installation and,
if mounted improperly, connect it certainly.
2
Is the action complete?
Review the DTC.
1. Using Tech 2, check and store the DTC.
2. Clear the DTC.
3
3. Perform test run and review the DTC.
Is DTC51 detected?
Action
3. Turn off the idle position switch for not less than 1
second but not more than 3 seconds. (Press the
accelerator pedal.)
4. Turn on the idle position switch for not less than 1
second but not more than 3 seconds. (Release the
accelerator pedal.)
5. 5. Turn off the idle position switch for not less than
1 second but not more than 3 seconds. (Press the
accelerator pedal.)
6. After the above operations are properly completed,
the CHECK ENGINE lamp (MIL) illuminates for 3
seconds to report the memory is cleared.
7. Turn off the starter switch. Wait for 5 seconds and
turn on the starter switch again.
When Tech 2 has been connected to the vehicle, the
DTC can be cleared through the memory clear
operation with Tech 2.
Diagnostic Aids
Poor connection or damaged harness may cause
intermittents. Check for the following conditions and, if
the fault is detected, repair or replace the faulty portion.
• Poor connection
connectors for backed-out pins, improper mating,
broken locks, improperly formed or damaged pins,
and poor pin-to-wire connection.
• Check the past service record for replacement of
ECM.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
3. If the DTC is not detected, the possible cause is
intermittent (intermittent fault).
Value(s)
—
Go to Step 2
—
Go to Step 3
—
Go to Step 4
at ECM: Inspect
Yes No
Refer to OBD
System Check
and go to Step 2
Refer to
Diagnostic Aids
harness
—