Oxygen Sensor Monitoring (Linear Upstream / Binary Downstream)
6. OXYGEN SENSOR MONITORING (LINEAR UPSTREAM / BINARY DOWNSTREAM)6.1 Upstream Oxygen Sensor Monitoring (linear)
Upstream Oxygen Sensor - Short Circuit Monitoring
Monitoring function:
The oxygen sensor circuit monitoring detects the malfunctions by evaluating the error information received from oxygen sensor microcontroller:
- Short circuit of sensor signal to battery voltage
- Short circuit of sensor signal to ECM ground
If one of the above mentioned malfunctions is detected, the corresponding fault code is stored.
Flowchart
Upstream Oxygen Sensor - Open Circuit Monitoring
Monitoring Description:
This function determines, if an open circuit in any of the four electric lines (Reference Voltage, Virtual Ground, Pumping Current and Trim Current) is present in the WRAF Sensor.
This function shall be triggered only if one of the following diagnosis has completed (to set the readiness bit), which are 'Upstream Oxygen Sensor - Signal Monitoring During Fuel Cut-off' and 'Upstream Oxygen Sensor - Heater Monitoring' and the WRAF sensor activity check. The function shall go to the state = "active" only if one of the above diagnosis detected a fault.
(Reference Voltage)
If a heater error exists and sensor voltage is too low, while the internal resistance measurement is turned off, an open circuit in the line 'Reference voltage' occurred. Before the internal resistance measurement is turned off, the sensor temperature-failure is stored.
(Virtual Ground) or (Pumping Current)
An open circuit in line Virtual Ground or in the line Pumping current can be detected if the sensor signal sticks near lambda 1. The sensor non-activity can be detected by the Oxygen Sensor Signal Monitoring During Fuel Cut-off (signal voltage below e.g. 2.1 V) in fuel cut off or WRAF sens activity check.
(Trim Current)
If the sensor shows an augmented gain, i.e. the sensor signal is higher than the nominal characteristic line, the plausibility test during the fuel cutoff phase shall detect this symptom (signal voltage above e.g. 5.6 V) during fuel cut off) and an Open Circuit is assigned to the line Trim Current.
Flowchart:
Upstream Oxygen Sensor - Signal Controller Monitoring
Diagnostic Overview:
Sec (e) (7.2)
This function will detect an error during the initialization and/or operation of a WRAF sensor controller through SPI communication. Information communicated from the Basic Software (BSW) is used for initialization and communication between application software (ASW) and the controller. This is used to determine if the function is working properly.
Monitoring Function:
Sec (e) (7.2.1)
After an ECU reset, the WRAF sensor controller is started and the diagnosis checks if the initialization has been performed in the allowed time. If not successful, then a DTC will be stored. If this is successful, then the last and current values of the communication error counter are compared in every diagnosis cycle. If differences are found too often, then the communication between CPU and sensor controller has a problem and the corresponding fault code is set.
All of the above checks are performed internal to the ECU. (See flowchart)
Flowchart:
Upstream Oxygen Sensor - Sensor-in-Air Check
Monitoring description:
The oxygen sensor in air check monitors if the sensor is attached to the exhaust pipe and whether the exhaust is sampled correctly (no leakage). A malfunction is detected if the oxygen sensor voltage is above a threshold (shows too lean mixture in part load or full load) for a specified time.
Flowchart:
Upstream Oxygen Sensor - Swapped Sensors Check
Monitoring Description:
This function will detect if the Oxygen Sensor wire harness has been cross connected, i.e., Bank 1 with Bank 2. This is performed by the use of the output of the fuel correction (lambda controller) of each bank. If this control is on opposite limits at bank 1 and bank 2, the sensors are swapped and the corresponding fault code is stored.
For a successful detection of the error, the symptom must have been detected in both high and low valve lift mode.
Flowchart:
Upstream Oxygen Sensor - Active Signal Check (Shift to lean / rich)
Monitoring Function
Sec (e) (7.1.1) (e) (6.2)
This monitor is an enhancement of the Downstream Oxygen Sensor - Active Signal Check (Stuck lean / rich) and the Trim Control Plausibility Monitoring. Its purpose is to help determine the root cause of a sticking downstream sensor signal or a implausible high I-share of the fuel trim controller.
The monitor will only be enabled if a fuel correction fault has been detected and a malfunction code has been stored or if the rear sensor signal check has detected, that the rear sensor signal is very rich or very lean and the corresponding malfunction fault code has stored.
If one of the listed fault codes exists, this diagnosis will be enabled to determine if the root cause of the malfunction is due to a stuck signal or characteristic line shift of the upstream O2 sensor or due to a stuck signal of the downstream O2 sensor or another system malfunction, i.e. vacuum leak, injector, etc...
If it has been determined that the upstream O2 signal was the root cause of the fuel correction fault, the appropriate DTC will be stored along with the fuel correction DTC or with the downstream sensor stuck DTC.
Sensor Monitoring - characteristic shift up to lean
Sensor Monitoring - characteristic shift up to rich
