Catalyst Monitor – What does it do? The catalyst monitor checks the efficiency of the catalytic converter by monitoring the upstream (pre-cat) and downstream (post cat) oxygen sensors. The ECM expects to see large fluctuations in the upstream oxygen sensor. But if the catalytic converter is doing it’s job, the ECM should see an almost flat line from the downstream oxygen sensor. To test the efficiency of the catalytic converter, carmakers will command a series of rapid fluctuations in air fuel mixtures. It will then watch the results of both … Read More
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