SENSORS IN OBD -II DIAGNOSTICS: STUDY ON EXHAUST GAS OXYGEN (EGO) SENSOR

Abstract

Increased awareness regarding the adverse effects of pollutants from automobile exhaust gases has been the main driving force for implementation of more and more stringent legislation on automobile exhaust emissions in many Countries. On Board Diagnostic (OBD), regulations in the USA for light and medium duty vehicles (I. C. Engines) are introducing to implement the air quality standard. California and the Federal Government used a driving cycle to certify 1966 and newer models which referred to as either California Cycle or the Federal Test Procedure (FTP).

 The California Air Resource Board (CARB) and the objective to reduce hydrocarbon (HC) emission caused by malfunction of the vehicles emission control systems adopted the California code of Regulations (CCR) known as OBD – II.

 The diagnosis is based on the oxygen sensor response time that is the amount of time to complete a switch from rich to lean or lean to rich transition that gives the ability to control the engine at stochiometric Air Fuel ratio. Typical values of lean mean voltage and rich mean voltage are 300 to 600 mill volts respectively. For post-cat O₂ sensor, in particular, voltage level checks and heater systems checked and done and the failure thresholds for the post O₂ sensor, diagnostic must not be set at a point beyond the failure limit where the catalyst diagnostic is affected.

 Enable Oxygen Sensor, this function checks for any condition that should inhibit the oxygen sensor diagnostic. The inputs to enable oxygen sensor are: Intrusive fuel control active state EGR map control state, fault active state, air fuel control and systems voltage.  Performance O₂ Response Tests:  Perform O₂ response tests consists of the following function:

Perform Oxy 1 – bank – 1 fast response test,

Monitor Oxy 1 – bank – 1 response,

Calculate Oxy 1 – bank – 1 response,

Perform Oxy 1 – bank – 1 slow response test.