Diagnostic trouble code: P0171 “Self adapting of closed loop control for air fuel
ratio exceeding the upper limit”
(Note: the following diagnostic procedures are applicable only under the
circumstances that the trouble codes of intake air pressure sensor, carbon canister
control valve, oxygen sensor and so on do not appear simultaneously, in case that such
trouble codes appear at same time, overhaul shall be carried out based on the
following procedures after dealing with other malfunctions firstly.)
Item
No.
Operation procedure
Inspection
results
Follow-up
procedure
1
Connect the diagnostic tester and adaptor,
and turn the ignition switch to “ON”
position.
Proceed to next
step.
Yes
Proceed to next
step.
2
Start up the engine, run at idle speed until
the temperature of coolant reaches the
normal value.
Under the full load working condition,
observe the value of “Oxygen sensor
voltage” on the diagnostic tester to verify
that the indicated value is maintained at
100 mV without significant change for
long time under certain working
conditions.
No
Refer to diagnosis
help.
Yes
Proceed to next
step.
3
Connect the fuel pressure gauge to the
feeding pipe of fuel supply system to
observe whether the fuel pressure is
maintained at 350kPa under full load
working condition.
No
Check and repair
the fuel system.
Yes
Repair and replace
the wiring harness.
4
Verify that the circuits between 36# and
18# pins of ECU and A# (corresponding to
the grey connecting wire of oxygen sensor)
and B# (corresponding to the black
connecting wire of oxygen sensor) pins of
the sensor connector are short to ground.
No
Proceed to next
step.
5
A. Verify that there is quite serious leakage
in the air intake system;
B. Verify that there is blockage in the fuel
injector;
C. Verify that the clearance of spark plug is
excessive large;
D. Verify that the resistance of distributor
circuit is excessive large;
E. Verify that the valve clearance is
excessive large; and etc.
Yes
Carry out service
based on the
diagnostic results.
G-32