Electronic Fuel Injection Control System 1B-12
the electronic control unit will immediately set the
fault information record in RAM fault memory,
and save it in the form of fault code, which will be
displayed according to the fault occurrence
sequence. According to the fault frequency, faults
can be classified into “Steady-state Faults” and
“Sporadic Faults” (like the faults resulting from
short-lived open circuit or poor contact between
connectors)
Fig. 2.4 Electronic Fuel Injection System’s Troubleshooting Principle
2.4.2 Classification of Fault Types
Diagnostic Fault Path and Fault Categories
Diagnostic fault path (DFP) is, in fact, a
sub-function for fault diagnosis that is used to
inspect functions of a given sensor, actuator, or
others in the EMS system. By respective
diagnostic path, the fault information will be
transmitted to the fault diagnosis management
module, which will take corresponding actions
and determine if the fault lamp should be activated
or the fault should be displayed on the diagnostic
unit. When a fault is detected at a given DFP, the
fault diagnosis management module will make
definite the fault type. Usually, the fault types
include:
B_mxdfp Maximum fault, signal goes beyond the
upper limit of the normal range.
B_mndfp Minimum Fault, the signal goes beyond
the lower limit of the normal range.
B_sidfp signal fault, without signal.
B_npdfp unreasonable signal, with signal, but
the signal is unreasonable.
Definitions of Fault Types
In this project there are 10 fault types. Closed fault
path is defined as “Class0”, namely, the fault
information will not enter the fault memory, and
also the diagnostic unit will not read the fault. In
addition, faults of Class2, Class3, Class4, Class5,
Class6, Class7, Class11, Class12, and Class13
belong to those fault types that have been defined
by the system in a uniform manner.
Class2: fault is inputted into the fault memory upon
taking place; DFP fault types relating to misfire are
usually defined as Class 2. As for the misfire fault
resulting in damage of catalyst, the MIL lamp will
flash in no time to prompt the driver. As for the
misfire fault resulting in deterioration of emission, if
the misfire fault of corresponding extent has been
fully detected in three consecutive driving cycles, the
MIL lamp will be activated, and also the fault will be
displayed on the diagnostic unit. If the fault fails to
be confirmed or eliminated in 40 driving cycles
(namely, in a warm-up cycle, E_xxx＝1, but Z_xxx
＝0), the fault information will be deleted from the
fault memory. if the fault disappears before the fault
confirmation and never occurs within 40 driving
cycles, the fault information will be deleted from the
fault memory; If the fault disappears after being
confirmed, the fault information cannot be deleted
from the fault memory until it does not occur within
40 warm-up cycles, and the fault priority is defined
as 20. After the fault confirmation, SVS lamp is off.
If the fault disappears after the fault confirmation and
never occurs within three driving cycles, it means
that the fault has been corrected.
Class3: fault is inputted into the fault memory upon
taking place. After the fault confirmation, the MIL
lamp is activated, and the fault confirmation needs
three driving cycles, with fault being displayed on the
diagnostic unit. If the fault fails to be confirmed or
eliminated within 40 warm-up cycles(namely, in a
warm-up cycle, E_xxx＝1, but Z_xxx＝0), the fault
information will be deleted from the fault memory; if
the fault disappears before the fault confirmation and
