Maintenance manual for sunray hfc4da1-2c china-IV diesel engines
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Section III. Fault Diagnosis
1. Fault Information Record
Electronic control unit continually monitors sensors, actuators, relevant circuits, MILs, battery voltage and even its
self and carries out reliability tests to sensor output signals, actuator drive signals and internal signals. Once there are
faults in certain link or certain signal is unreliable, electronic control unit sets fault information record in RAM fault
memory immediately. Fault information record is stored in the form of diagnostic trouble code (DTC) and shown in
the sequence of fault occurrence.
Faults can be divided into “steady fault” and “random fault” (such as faults caused by temporary open circuit of
harness or poor contact of connectors) according to fault occurrence frequency.
2. Fault Condition
If duration of an identified fault exceeds set stabilization time for the first time, ECU identifies it as a steady fault and
stores it as a “steady fault”. If the fault disappears, ECU identifies it as a “random fault” and “nonexistent”. If the fault
is identified once again, it is still a “random fault”. However, “existent” historical faults will not influence normal
application of engine.
3. Fault Type
Short to power supply positive pole
Short or open to ground (In the case of pull-up or pull-down resistor for input stage, ECU will identify open circuit
failure of input port as the fault of input port short to power supply positive pole or short to ground)
Unreliable signal
4. Fault Frequency Counter
For every identified fault, there is an individual frequency counter value (HZ). Frequency counter value (Hz)
determines storage time of corresponding fault information record in the memory after fault disappearance (fault
elimination).
For the first time fault identification, it (Hz) is set to be its initial value as 40. If fault condition does not change, this
value will maintain the same forever.
Once identified fault has disappeared and then the condition has been maintained for certain period of time, the value
(Hz) is reduced by 1 after every successful engine start (engine speed exceeds that of engine start completion). At this
moment, ECU recognizes the fault has disappeared but fault information record still exists.
If the fault (such as fault caused by poor contact) appears and disappears frequently, the value (Hz) is increased by 1
but the value will not exceed set upper limit of 100.
When the value (Hz) becomes zero, all fault information records in the fault memory are cleared completely.
5. Fault Alarm
In the case of electronic control system, when there are faults in some important components such as ECU, coolant
temperature sensor, phase sensor, boost pressure sensor, revolution speed sensor, air flow meter, fuel injector, fan relay
and etc, ECU will give alarms via MIL flashing until faults are eliminated.
6. Fault Reading
Fault information records can be brought out from electronic control unit via fault diagnostic apparatus. However,
some faults can be detected only when vehicle reaches corresponding operation condition.
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