Contents: Heating of sensors 🠛 Upper sensor signal voltage 🠛 Lower sensor signal voltage 🠛 Correction of the composition of the…🠛 Start of regulation of fuel mixture…🠛 Phase "opening the control loop" 🠛 Backup mode in case of oxygen sensor…🠛
Note: Engine with ECU "BOSCH ME 7.4.6" equipped with two oxygen sensors for each bank of cylinders: upper and lower.
Heating of sensors
Heating of oxygen sensors is switched on by the ECU command if:
- battery voltage below 15V;
- after a 4-second time delay has elapsed after startup.
Heating of the oxygen sensors is stopped if regulation is carried out depending on the temperature. It is maintained at 750°C.
Upper sensor signal voltage
Read the value of the parameter: "upstream sensor signal voltage" on the diagnostic tool: this is the voltage value that is transmitted to the ECU by the oxygen sensor installed before the catalytic converter. The voltage value is expressed in millivolts. When the engine is running in a closed control loop, the voltage should quickly fluctuate between two values:
- 100 mV ±100 for lean mixture;
- 800 mV ±100 for rich mixture.
The smaller the difference between the minimum and maximum values, the less accurate the information from the sensor (typically this difference should be at least 500 mV).
Note: If this difference is small, check the sensor heating.
Lower sensor signal voltage
It is necessary to read the value of the parameter: "lower sensor signal voltage" on the diagnostic device. This is the voltage value that is transmitted to the ECU by the oxygen sensor installed after the catalytic converter. The voltage value is expressed in millivolts.
This sensor is designed for diagnostics of the catalytic converter and repeated, more accurate, control of the mixture composition (slow control loop). This function is activated only after the engine has been running for some time.
When the motor is running in closed loop, the voltage should vary within the range of 600 mV ±100. When the speed is reduced, the voltage should be below 200 mV.
The voltage value read from the diagnostic tool at idle speed should not be taken into account.
Correction of the composition of the working mixture
The value of the parameter "correction of the working mixture composition", read by the diagnostic device, is the average value entered by the ECU depending on the information about the composition of the working mixture transmitted by the oxygen sensor installed in front of the catalytic converter (in reality, the oxygen sensor analyzes the oxygen content in the exhaust gases).
The average correction value is 1.
Value below 1: lean request.
Value above 1: request for enrichment.
Start of regulation of fuel mixture composition
Regulation of the composition of the working mixture begins after a time delay after starting the engine and regardless of the coolant temperature.
Article reprinted from the website renaultbook
The time delay after engine start can vary between 0 and 70 s.
Phase "opening the control loop"
When regulating the composition of the working mixture, the ECU does not take into account the value of the sensor signal voltage in the following cases:
- with the accelerator pedal pressed all the way down;
- during sudden acceleration;
- when decelerating with fuel cut-off;
- if the oxygen sensor fails.
Backup mode in case of oxygen sensor failure
If the voltage signal from the oxygen sensor when regulating the composition of the working mixture is incorrect (changes very little or not at all), then the ECU switches to the backup mode only if the fault has been determined as present for 3 minutes. Only in this case will the fault information be entered into the ECU memory. In this case, the value of the "fuel mixture correction" parameter is 1.
When a fault is detected in the oxygen sensor, if the fault information is already stored in the memory, the ECU immediately switches the engine to open-loop operation.