Oxygen Sensor: Description and Operation

The exhaust gas passes from the exhaust manifold to the catalytic converter assembly, where reactions take place to reduce the levels of pollutants at the tail pipe. The heated oxygen sensors (HO2S) (29,and 30 upstream of the catalysts, 31 and 32 downstream) compare the level of oxygen in the exhaust gas to that in the atmosphere and produce an output signal-which is used by the engine closed loop fuel strategy to make fuelling corrections, and thus help control overall emission levels. Also comparison of upstream and downstream signals allows determination of catalyst conversion efficiency. The sensors contain integral heaters (under ECM control) to allow them to reach optimum operating temperature in a short time after engine start.

Fig. 1 EMS System Schematic:

1. Intake Air Temperature Sensor
2. A-Bank Air Cleaner
3. B-Bank Air Cleaner
4. Throttle Position Sensor
5. A-Bank Idle Air Control Valve
6. B-Bank Idle Air Control Valve
7. A-Bank Evap. Emission Purge Control Solenoid Valve
8. B-Bank Evap. Emission Purge Control Solenoid Valve
9. Evap. Emission Purge Control Canister
10. A-Bank Manifold Absolute Pressure Sensor
11. A-Bank Fuel Filter
12. B-Bank Manifold Absolute Pressure Sensor
13. B-Bank Fuel Filter
14. Camshaft Position Sensor
15. Engine Position Sensor
16. Engine Speed Sensor
17. A-Bank Fuel Injectors
18. B-Bank Fuel Injectors
19. Fuel Pressure Regulator
20. Fuel Tank
21. Main Fuel Pump
22. Secondary Fuel Pump
23. Fuel Level Sensor
24. Engine Coolant Temperature Sensor
25. A-Bank Ignition Amplifier
26. B-Bank Ignition Amplifier
27. A-Bank Ignition Coil
28. B-Bank Ignition Coil
29. A-Bank Upstream Heated Oxygen Sensor
30. B-Bank Upstream Heated Oxygen Sensor
31. A-Bank Downstream Heated Oxygen Sensor
32. B-Bank Downstream Heated Oxygen Sensor
33. Secondary Air Injection Pump
34. Secondary Air Injection Switching Valve
35. Vacuum Solenoid Valve
36. A-Bank Secondary Air Injection Check Valve
37. B-Bank Secondary Air Injection Check Valve
38. Ignition Supply
39. Engine Control Module
40. Malfunction Indicator Lamp / Instrument Pack
41. Battery
42. Cranking Signal
43. Security and Locking Control Module
44. PDU / Generic Scan Tool
45. Transmission Control Module (5 lines)
46. Air Conditioning Control Module (4 lines)
47. Park Neutral Switch
48. Power Steering Pressure Switch