New Catalytic converter/w 02 port

Asked by Curtis May 07, 2022 at 09:41 AM about the 2003 Pontiac Grand Am GT

Question type: Maintenance & Repair

I replaced my catalytic converter and new downstream O2
sensor. The original cat didn't have an O2 port. It was
behind the cat. I used the O2 port and the service light went
out on my way home from work. This morning while on my
way to work the service engine light came back on. The car
is running rough and I smell something like diesel exhaust.
Should I remove the O2 sensor, plug the port, and add a 02
pipe on the back of converter?

155,195

james answered about a year ago

The downstream oxygen sensor needs to be behind the catalytic converter in the exhaust system. In other words, between the catalytic converter and the tailpipe. The only thing it does is monitor the catalytic converter's performance. The upstream oxygen sensor should be ahead of the catalytic converter in either the exhaust system or the exhaust manifold(s). This oxygen sensor is responsible for helping to maintain the proper air to fuel mixture of the engine. It sounds like you have them transposed or you have the wrong catalytic converter or the parts store gave you an upstream oxygen sensor instead of the downstream oxygen sensor. If you bought a universal converter the original converter gets cut out of the exhaust system and the universal converter will be installed in its place. What you're smelling is the catalytic converter overheating because the engine is not running right. Most likely because of the oxygen sensor problem. Hook the downstream oxygen sensor up where it was originally. Hope that helps! Jim

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