Posts Tagged: Catalyst Monitor

Catalyst Monitor — What does it tell you

Learn what the catalyst monitor means and what it’s telling you 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 its job, the ECM should see an almost flat line from the downstream oxygen sensor. To test the efficiency of the catalytic converter, the software will command a series of rapid fluctuations in air-fuel mixtures, from rich-to-lean and lean-to-rich. It … Read More