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On Board Diagnosis Logic
NHEC0173
With the Air/Fuel Mixture Ratio Self-Learning Control, the actual mixture ratio can be brought closely to the
theoretical mixture ratio based on the mixture ratio feedback signal from the heated oxygen sensors 1 (front).
The ECM calculates the necessary compensation to correct the offset between the actual and the theoretical
ratios.
In case the amount of the compensation value is extremely large (The actual mixture ratio is too rich.), the
ECM judges the condition as the fuel injection system malfunction and light up the MIL (2 trip detection logic).
Sensor Input Signal to ECM
ECM func-
tion
Actuator
Heated oxygen sensors 1 (front)
Density of oxygen in exhaust gas
(Mixture ratio feedback signal)
Fuel injec-
tion control
Injectors
Malfunction is detected when fuel injection system does not operate properly, the amount of mixture ratio
compensation is too large.
(The mixture ratio is too rich.)
Possible Cause
NHEC0488
I Heated oxygen sensor 1 (front)
I Injectors
I Exhaust gas leaks
I Incorrect fuel pressure
I Mass air flow sensor
SEF215Z
DTC Confirmation Procedure
NHEC0174
NOTE:
If “DTC Confirmation Procedure” has been previously conducted,
always turn ignition switch “OFF” and wait at least 10 seconds
before conducting the next test.
WITH CONSULT-II
NHEC0174S01
1) Start engine and warm it up to normal operating temperature.
2) Turn ignition switch “OFF” and wait at least 10 seconds.
3) Turn ignition switch “ON” and select “SELF-LEARNING CONT”
in “WORK SUPPORT” mode with CONSULT-II.
4) Clear the self-learning control coefficient by touching “START”.
5) Select “DATA MONITOR” mode with CONSULT-II.
6) Start engine again and let it idle for at least 10 minutes.
The 1st trip DTC P0172, P0175 should be detected at this
stage, if a malfunction exists. If so, go to “Diagnostic
Procedure”, EC-304.
7) If it is difficult to start engine at step 6, the fuel injection sys-
tem has a malfunction, too.
8) Crank engine while depressing accelerator pedal.
If engine starts, go to “Diagnostic Procedure”, EC-304. If
engine does not start, remove ignition plugs and check for
fouling, etc.
DTC P0172 (BANK 1), P0175 (BANK 2) FUEL INJECTION SYSTEM FUNCTION
(RICH)
On Board Diagnosis Logic
EC-300
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