P0136

DTC P0136 HO2S-2 CIRCUIT MALFUNCTION





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 three 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.
1) 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 oxygen sensor-1 increases and a rich signal is sent to ECM.
2) Upon receipt of the rich signal, ECM decreases the amount of fuel injection, which causes oxygen concentration in the exhaust gas to increases and the electromotive force of the oxygen sensor 1 to decrease. Then a lean signal is sent to ECM.
3) 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).





DETECTING CONDITION





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, on a level road.

NOTE: Check to make sure that following conditions are satisfied when using this DTC CONFIRMATION PROCEDURE.
- Fuel level : higher than 1/4 (fuel level meter indication).
- Intake air temp.: -14°C, 6.8°F or higher.
- Atmospheric pressure (Altitude) : 540 mmHg, 72 kPa or more (2790m, 9150 ft or less).

1) Connect scan tool to DLC with ignition switch OFF.
2) Turn ON ignition switch and clear DTC, pending DTC and freeze frame data by using scan tool.
3) Start engine and warm up it completely.
4) Increase vehicle speed to 56 km/h (35 mph) or more.
5) Keep driving above vehicle speed for 5min or more (Change of vehicle speed is permitted in this step).
6) Increase vehicle speed to 80 - 96 km/h (50 - 60 mph) (engine speed: 2.500 - 3,000 r/min).
7) Keep driving above vehicle speed for 1 min (Throttle valve opening is kept constant in this step).
8) Release accelerator pedal and with engine brake applied, keep vehicle coasting and then stop vehicle.
9) Check pending DTC and DTC by using scan tool.





TROUBLESHOOTING