Circuit Description
Secondary Air Injection Reaction (AIR) system is controlled by PCM. System aids in reduction of first and second cycle hydrocarbon emissions. During open loop fuel control, PCM energizes AIR system. Air is injected into exhaust stream for a specified amount of time. Heat generated from post-combustion oxidation helps catalytic converter reach operating temperature sooner (converter light-off).
The following conditions determine pump operation and run time:
- Start-up ECT and IAT must be 59-230°F (15-110°C).
- If ECT sensor signal indicates an engine temperature greater than 158°F (70°C), total pump on time is 40 seconds.
- If ECT sensor signal indicates an engine temperature less than 158°F (70°C), total pump on time is 100 seconds.
PCM monitors AIR system in 2 stages, passive and active. PCM initiates a 2 part passive test (stage 1) once each ignition cycle. Part one monitors HO2S response when PCM commands air pump on. If HO2S remains proportionally lean (low HO2S signal) for a minimum of 5 seconds, part 1 passes and part 2 of passive test is initiated.
Second part of passive test monitors transition from open loop to closed loop fueling. When air injection to exhaust is commanded off, PCM monitors HO2S response. If HO2S signal switches from a lean to rich condition for a specific amount of time, part 2 passes. If part 1 and part 2 pass, further monitoring of AIR system is discontinued. If any portion of passive test fails, PCM initiates active test (stage 2).
To run active test, air pump is commanded on during warmed-up, closed loop operation. PCM monitors HO2S, and long and short term fuel trim value response to air injection. If HO2S signal remains proportionally lean (low HO2S signal), and long and short term fuel trim values increase for a specific amount of time, active test passes. If HO2S, and long and short term fuel trim values do not respond to air injection, active test fails.
If PCM detects a consecutive number of active test failures, appropriate DTCs will set. If a successful test occurs during active test stage, a pass indication results and test will not run until next ignition cycle.