C.3 Oxygen Sensor Voltage Typical displays to view OS voltage are either 001–004 (basic) or 026/033. You may see some combination of the following parameters: • O2SENSOR(V) • O2SENSOR1(V) • O2SENSOR2(V) • O2SENSOR(BANK1)(V) • O2SENSOR(BANK1,AFTERCAT)(V) • O2SENSOR(BANK1,BEFORECAT)(V) • O2SENSOR(BANK2)(V) • O2SENSOR(BANK2,AFTERCAT)(V) • O2SENSOR(BANK2,BEFORECAT)(V) • O2SENSOR(BK1-SNS1)(V) • O2SENSORAFTERCAT(V) • O2SENSORAFTERCATBK1(V) • O2SENSORAFTERCATBK2(V) • O2SENSORBEFORECAT(V) These parameters indicate the amount of oxygen in the exhaust gas. High oxygen levels indicate a lean air/fuel mixture, while low oxygen levels indicate a rich air/fuel mixture. When the O2Ss are at operating temperature and the system is operating in closed loop, the ECM constantly adjusts the air/fuel mixture to achieve a 14.7:1 ratio. The ECM uses OS signals to determine how rich or lean the engine is running and to correct the mixture. C.4 Early Vehicle Oxygen Sensor Reading Many early vehicles, model years 1990–93, with limited display groups may not read OS or O control. However, you can use Expert Mode and select display group 000. O2V reads in binary
163 Fuel Control Learning Adaptation Values Late Model Oxygen Sensor Reading format (0–255). There is no consistency, but Channel 5 often reads the O signal. Look for this number to be constantly varying up and down by at least 14 digits. If Channel 5 is not active, it maybe an application that only displays an O short term FT factor. In this case, check channel 4. The O control factor will also output a binary 0–255 number with 128 as the midpoint. Numbers less than 128 indicate a rich mixture correction. Numbers higher than 128 indicate a lean mixture correction. Look for fast fluctuations at different RPM and load conditions which indicate an active OS (use DVOM to test OS directly. Above is for those vehicles with display group 000 only. On vehicles with additional display groups but still not displaying O2V directly, look at the O Factor which reads 1.0 as the base point. Higher numbers indicate correction fora mixture too lean and lower numbers indicate a correction fora mixture too rich. Atypical normal range is 1.0 The following sections are display examples for late model OBD-II OS and CAT tests. C.4.1 Example Motronic 2.9 (1993–1995) The following example concerns reading engine data display Group Display group 000 has 10 channels or display fields, listed below. 1. Coolant temperature 2. Engine load 3. RPM 4. O2 factor 5. Idle Adapt 6.