11. DTC: P0171, Air Fuel Ratio Closed Loop Control Self-adaptation Upper Limit Break (see Table (1-24) (Note: If the DTC related to intake air pressure sensor, canister control valve, oxygen sensor is produced, please remove these troubles at first, and then go to the following steps.) Table 1-24 51 S/N Operation Test Results Actions 1 Connect the diagnostic instrument and adapter, and turn the ignition switch to ON. Next step 2 Start the engine, and keep idle speed until the coolant reaches the normal temperature. Check the “oxygen sensor voltage” on the diagnostic instrument. At this moment, does it keeps around 100mV for a long time under certain working conditions?
Yes Next step No Diagnosis help 3 Connect the fuel pressure gauge to the intake end of the fuel system. Check if the fuel pressure keeps around 380kPa. Yes Next step No Check and repair fuel system 4 Check for short to ground between pin 36#, 18# of the ECU and pin A# (to the grey connection line of the oxygen sensor), B# (to the black connection line of the oxygen sensor) of the sensor with a multimeter. Yes Repair or replace harness No Next step 5 A. Check the intake air system for serious leakage; B. Check if the fuel injector is blocked; C. Check the spark plug for over-sized gap D. Check the distribution line for overhigh resistance; E. Check the valve for over-sized gap.
Yes Check and repair as per diagnosis No Diagnosis help