Oxygen Sensor Monitoring
Oxygen Sensor MonitoringThe Lambda control consists of a linear oxygen sensor upstream catalyst and a 2 point oxygen sensor downstream catalyst
O2S front open circuit diagnosis manager
To detect open lines at the O2S front, an open circuit diagnosis manager (internal ECU software) handles the logical information from the following diagnostics.
- Functional check heater
- Signal activity check
- Intrusive check temperature measurement
Combinations and outcome of these diagnoses lead to the different failure location for open circuit.
Open circuit (UN)
If the functional check heater failed and the intrusive check temperature measurement failed, an open circuit in the line for Nernst voltage exists.
Open circuit (VM)
An open circuit in line Virtual Mass can be detected if the functional check heater failed and the signal activity checks failed.
Open circuit (IP)
If the sensor signal activity check failed and no failure for the heater is detected, an open circuit in line Pumping current exists.
Open circuit (IA)
The signal activity check during fuel cut-off detects a malfunction, if the oxygen sensor signal is above a defined range. The open circuit diagnosis manager identifies an open line for adjustment voltage.
O2S front Functional check heater
The purpose of this function is to detect oxygen sensor heater failures.
After engine start the diagnosis monitors the time required to reach O2S readiness. Is the time threshold exceeded and no other O2S failure exists, the heater is defective and the failure management is triggered.
After O2S readiness, the ceramic temperature is continuously monitored for an upper and lower threshold. If the ceramic temperature exceeds one of the thresholds and no other O2S failure exists, the heater is defective and the failure management is triggered. If other O2S failures exist, the diagnosis result is handed over to the open circuit diagnosis manager.
O2S front Signal activity check
The purpose of this function is to detect an insufficient deflection of the O2S signal. For a time period the lambda deflection is accumulated and has to exceed a threshold. If the threshold is not exceeded, the diagnosis result is handed over to the open circuit diagnosis manager.
O2S front Signal activity check (fuel cut off)
The oxygen sensor signal monitoring during fuel cut-off detects if the oxygen sensor signal is below a defined range. The diagnosis result is handed over to the open circuit diagnosis manager.
O2S front Intrusive check temperature measurement
If the functional check for the heater has detected a failure, the oscillator of the O2S controller (ATIC 42) used to measure the sensor internal resistance is disabled in order to allow a more detailed error detection. Does the O2S signal falls below a threshold for a certain time during the defined diagnosis period it is an indicator for a broken VN-line. In any case the result of this test is handed over to the open circuit diagnosis manager either to enter the failure in the error management or to proceed with further diagnostics.
O2S front Signal range check
The purpose of this diagnosis is to determine that the O2S front signal is in the proper working range. Exceeds the signal voltage under non-idle conditions the threshold, a malfunction is detected.
O2S front rationality check high/low
The purpose of this diagnosis is to determine character shift down or up of the O2S front. If the O2S rear indicates rich conditions and lambda controller deviates to rich side but O2S front signal remains on the lean side then a character shift down malfunction of the O2S front is detected.
A character shift up malfunction of the O2S front is detected, if the O2S rear indicates lean conditions and lambda controller deviates to lean side but O2S front signal remains on the rich side.
O2S front Response check
The purpose of this diagnosis is to determine if the dynamic behavior of the O2S front signal is in range for proper function.
O2S rear oscillation check
Does the O2S rear signal voltage not oscillating at reference for a defined period of time the lambda set value is significantly shifted to rich/lean under open loop conditions. The reaction of the O2S rear signal voltage will be evaluated against thresholds for malfunction.
O2S rear Signal range check
The purpose of this diagnosis is to monitor the required range for proper operation. If the signal voltage, under fuel cut off conditions, does not fall below the threshold for a specified mass airflow integral, a malfunction is detected.
O2S heater out of range
The purpose of this diagnostic is to determine insufficient power of the heater for the downstream O2-sensor. It is monitored whether the resistance of the rear O2-sensor is below a threshold. If not, the heater has insufficient power.
