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Automotive Emissions and Onboard Diagnostics

by John West & Mark Stachew

Start ý Why Onboard Diagnostics? ý Major Components ý Catalytic Converter ý Oxygen Sensor ý EGR ý Fuel System Adaptive Learning ý Misfire Detection ý The Need for Speed ý New Regulations ý 0 to 100 KB in 6 Seconds ý Sources and PDF

MAJOR COMPONENTS

To comply with OBD II, new vehicles contain and monitor the operation of the following emissions components:

• Catalytic converters
• Oxygen sensors located upstream and downstream of the catalytic converter (most of which are heated)
• EGR (exhaust gas recirculation) valve that is electronically operated
• Fuel system adaptive learning
• Evaporative emission control systems (canister purge and vent solenoid)
• Misfire detection (both hardware and software)
• Secondary air system

The primary components in emissions control are the catalytic converter and oxygen sensors. These devices are among the most expensive emissions components in a vehicle, containing such precious metals as platinum, palladium, and rhodium (two to seven times the price of gold (US $).

In addition to these components, OBD II has driven the evolution of the engine control unit (ECU). Todayýs automotive microcontrollers, the main processor of the ECU, contain 1 MB of flash memory and 32 KB of RAM, operate at speeds greater than 40 MHz, integrate floating point units, and have timing and communications coprocessors. Some of todayýs ECUs contain multiple microcontrollers, 5 to 10 MB of external flash memories, and complex digital and analog ASICs.

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