The normal oxygen sensor signal voltage is constantly changing around 500 mV, and the front sensor signal frequency is at least 5 Hz at 2500 min-1. As a result of the catalytic converter, the rear oxygen sensor signal frequency is lower than the front oxygen sensor signal frequency. If the frequency of the signal of the rear oxygen sensor for a long period of time coincides with the frequency of the signal of the front oxygen sensor, this indicates a decrease in the efficiency of the catalytic converter or a malfunction in the engine power system.
Pic. 2.247. Oxygen concentration sensor
Pic. 2.248. Scheme of connections of the oxygen concentration sensor with the ECU
Conditions for storing fault codes
The ECU stores a fault code and the engine control system malfunction indicator lamp lights up when an open or short circuit is detected in two driving cycles «mass» in the injector circuit.
Code P0130
In each driving cycle after the engine is started, the ECU checks the front oxygen sensor once within 5 seconds. If, in two driving cycles, the front oxygen sensor signal voltage is not between 0 and +380 mV while the rear oxygen sensor signal voltage is above 350 mV, the ECU issues a fault code and turns on the engine control system malfunction indicator lamp. This code indicates that the ECU has detected a malfunction of the front oxygen sensor.
Code P0136
After the system enters the closed loop control and 3 minutes of engine operation, the ECU checks the signal voltage of the rear oxygen sensor. If the rear oxygen sensor signal voltage is not between 400 and 500 mV for two driving cycles, the ECU issues a DTC and turns on the engine management system malfunction indicator lamp. This code indicates the presence of abnormal readings from the rear oxygen sensor or the ECU after the engine has warmed up for 3 minutes.
Code P0131
3 minutes after turning on the heating of the front oxygen sensor, the engine control unit continuously measures the signal voltage of the front oxygen sensor at intervals of 0.5 s. If the front oxygen sensor signal voltage is below 50 mV for 0.5 seconds for two driving cycles, the ECU will set code P0131 and the engine control system malfunction indicator lamp will turn on. The output of this code indicates that the front oxygen sensor or ECU determines a strong lean mixture.
Code P0131
After the system enters a closed control loop and after 3 minutes of engine operation, the ECU checks the signal voltage of the rear oxygen sensor for 0.5 seconds. If the rear oxygen sensor signal voltage is below 50 mV for two driving cycles, the ECU will set code P0137 and the engine management system malfunction indicator lamp will turn on. The output of this code indicates an extremely low signal voltage of the rear oxygen sensor.
Code P0132
3 minutes after turning on the heating of the front oxygen sensor, the engine control unit continuously measures the signal voltage of the front oxygen sensor at intervals of 0.5 s. If the front oxygen sensor voltage exceeds 1.058 volts for 0.5 seconds for two driving cycles, the ECU sets code P0132 and the engine control system malfunction indicator lamp comes on. The output of this code indicates an excessive enrichment of the fuel-air mixture.
Code P0138
After the system enters a closed control loop and after 3 minutes of engine operation, the ECU checks the rear oxygen sensor signal for 0.5 seconds. If the rear oxygen sensor signal voltage exceeds 1.058 volts for two driving cycles, the ECU outputs code P0138 and the engine control system malfunction indicator lamp comes on. The output of this code indicates an excessively high signal voltage of the rear oxygen sensor.
Code P0133
The engine control unit memorizes the code P0133 and the engine control system malfunction indicator lamp lights up if the parameters listed below are not detected by the computer in two driving cycles.
1. Within 2 minutes, the ECU should determine the compensation ratio of the fuel component of the mixture is greater than 85% or less than 95%.
2. The ECU must make some correction of the fuel-air mixture when:
- crankshaft speed is within 1600–3200 min-1;
- engine load is in the range of 1.35–3.4 ms;
- the temperature of the catalytic converter is above 372°C;
- the system is in a closed control loop.
The output of this code indicates that the ECU does not properly correct the composition of the fuel-air mixture according to the signals of the front oxygen sensor or does not correct it at the required frequency after the engine warms up or during normal engine operation.
Code P0134
After 3 minutes of engine operation, the ECU checks the signal voltage of the front oxygen sensor. If the front oxygen sensor signal voltage is not between 400 and 600 mV for 5 s during two driving cycles, the ECU generates a code and the engine control system malfunction indicator lamp lights up. The output of this code indicates that after the engine has warmed up, the signal voltage of the front oxygen sensor is not within the required limits.