P0131

WIRING DIAGRAM

CIRCUIT DESCRIPTION
It is necessary to keep the air/fuel mixture close to the theoretical air/fuel ratio (14.7) to obtain efficient performance of the 3-way catalytic converter and high clarification rate of CO, HC and NOx in the exhaust gas. For that purpose, ECM operates as follows. It first compares the signal from the heated oxygen sensor-1 with a specified reference voltage and if the signal is higher, it detects that the air/fuel ratio is richer than the theoretical air/fuel ratio and reduces fuel. On the other hand, if the signal is lower, it detects that the air/fuel ratio is leaner and increases fuel. By repeating these operations, it adjusts the air/fuel ratio closer to the theoretical air/fuel ratio.
- When oxygen concentration in the exhaust gas is low, that is, when the air/fuel ratio is smaller than the theoretical air/fuel ratio (fuel is richer), electromotive force of the heated oxygen sensor increases and a rich signal is sent to ECM.
- Upon receipt of the rich signal, ECM decreases the amount of fuel injection, which causes oxygen concentration in the exhaust gas to increase and electromotive force of the heated oxygen sensor to decrease. Then a lean signal is sent to ECM.
- As ECM increases the amount of fuel injection according to the lean signal, oxygen concentration in the exhaust gas decreases and the situation is back to above 1).
This control process, however, will not take place under any of the following conditions.
- At engine start and when fuel injection is increased after engine start
- When engine coolant temperature is low
- When highly loaded and fuel injection is increased
- At fuel cut
- When heated oxygen sensor is cold
- When engine is running at high speed (higher than about 4000 r/min).





DETECTING CONDITION AND POSSIBLE CAUSE

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 with 2 persons, a driver and a tester.

1. Turn ignition switch OFF. Clear DTC with ignition switch ON, check vehicle and environmental condition for:
- Indication of fuel level meter in combination meter: 1/4 or more
- Altitude (barometric pressure): 2400m, 8000ft or less (560mmHg, 75kPa or more)
- Ambient temp.: -10°C, 14°F or higher
- Intake air temp.: 50°C, 122°F or lower
2. Warm up engine to normal operating temperature.
3. Drive vehicle at 30 - 40mph, 50 - 60km/h for 2 min.
4. Stop vehicle and run engine at idle for 2min.
5. Check DTC in "DTC" mode and pending DTC in "ON BOARD TEST" or "PENDING DTC" mode.





INSPECTION