Service manual

Chapter Two Fundamental Principle for Failure Diagnosis of
Electronic Fuel Injection System
1. Failure Information Records
The ECU monitors sensor, actuator, related circuit, malfunction indicator and
battery voltage etc., and even EUC itself continuously. At the same time, the ECU
inspect the reliability test on sensor signal output, actuator driving signal and internal
signal (e.g.: closed loop control, knock control, idle speed control and accumulator
voltage control etc.). ECU will set the malfunction record on RAM malfunction
memory immediately once the malfunction or the unlikelihood signal is detected. The
failure information records are stored in the form of diagnostic trouble code (DTC) and
are displayed in the precedence order of occurrence of the failures.
Failures can be divided into “stable state failures” and “random failures” (for example,
caused by transient open circuit of wires or poor contact of inserted parts) by failure
frequency.
2. Failure State
Once duration of occurrence of an identified failure exceeds the given stabilization time
for the first time, ECU will account it as a stable failure and then store it as a “stable
state failure”. If this failure disappears, it will be stored as a “random failure” and
“non-existent”. If this failure is identified again, it will still be a “random failure”, but a
“existent” early failure that will not affect average service of the engine.
3. Failure Types
Short circuit to positive pole of power supply
Short circuit to ground
Open circuit (for the case where there are pull-up resistors or pull-down resistors during
input stage, ECU will recognize failure of open circuit at input port as that of short
circuit to positive pole of power supply or that of short circuit to ground)
Signals can not be used
4. Failure Frequency Counter
For every identified failure, a separate frequency counter numerical value (Hz) will be
set.
This numerical value (Hz) for frequency counter determines the time this failure