P0172
DTC P0171 / P0172: System Too Lean / Too Rich (Sensor-1, Bank-1)Wiring Diagram
Wiring Diagram:
A/F Sensor Description
A/F sensor (1), in place of the conventional HO2S-1, is installed in the center of the exhaust manifold joining section and it consists of a zirconia element (2) which causes the output current to vary according to difference in the oxygen concentration and a heater (3) which activates the element.
A/F sensor detects oxygen concentration in exhaust gas (9) (A/F ratio of the air-fuel mixture) linearly, ranging from LEAN to RICH.
Operation
ECM (5) controls the sensor heater (3) and keeps the sensor element temperature at the specified level (about 750 °C) constantly so that the A/F sensor is activated in the specified way for accurate A/F detection. When the sensor element reaches the specified temperature (it is activated), its impedance drops to the specified value (approx. 30 ohms) by its characteristic. When a certain voltage (about 0.4 V) is applied between sensor elements in this state, circuit current corresponding to the sensor element impedance flows in the sensor circuit. ECM detects this circuit current and judges whether the sensor is in the active state or not. At this time, sensor current is output linearly in the range of +0.01 mA to +some mA on the lean side and -0.01 mA to -some mA on the rich side. The variation in these ranges depends on the difference from the stoichiometry A/F ratio, that is, the amount of oxygen between the atmosphere side and exhaust manifold (7).
According to this sensor output, ECM executes A/F feedback (fuel trim) to achieve the target A/ ratio.
DTC Detecting Condition and Trouble Area
DTC Detecting Condition And Trouble Area:
DTC Confirmation Procedure
WARNING:
^ When performing a road test, select a place where there is no traffic or possibility of a traffic accident and be very careful during testing to avoid occurrence of an accident.
^ Road test should be carried out by 2 persons, a driver and a tester, on a level road.
NOTE: Check to make sure that the following conditions are satisfied when using this "DTC Confirmation Procedure".
EVAP leak check model:
^ Altitude (barometric pressure): 2400 m, 8000 ft or less (560 mmHg, 75 kPa or more)
^ The following DTCs are not detected: DTCs related to MAF sensor and A/F sensor
Non-EVAP-leak-check model:
^ Intake air temperature at engine start: -10 °C (14 °F) to 80 °C (176 °F)
^ Intake air temperature: -10 °C (14 °F) to 70 °C (158 °F)
^ Altitude (barometric pressure): 2400 m, 8000 ft or less (560 mmHg, 75 kPa or more)
^ The following DTCs are not detected: DTCs related to MAF sensor, ECT sensor, IAT sensor, barometric pressure sensor and A/F sensor
1. With ignition switch turned OFF, connect scan tool.
2. Turn ON ignition switch and print Freeze Frame Data or write them down using scan tool.
3. Clear DTC using scan tool.
4. Start engine and warm up to normal operating temperature.
5. Operate vehicle with condition as noted freeze frame data for 5 min.
6. Stop vehicle and check DTC and pending DTC.
DTC Troubleshooting
