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Will the CEL turn on if I delete the cats?


Topic starter

Hello Mr. Scotty, I have a 2005 Gmc Sierra 1500 Stl. It over 200,000 miles on it, but she still runs well. The couple of questions I had are 1st, I had the catalitc converters removed, but I think it is causing my engine light to come on. I have the sensors in the exhaust where they were located... But I just wanted to know if I should put some back on. Secondly, the a/c doesn't come on properly. The panel will show it is on...but it comes on when it gets ready. And when it does, it's hot air. It has been blowing cold in the past. I was recently in a collision with it, so I am assuming that they had to unplug the battery. Also I think the battery may be weak. Could a new battery help with the problem? Thanks for your help in advance. 👍🏾

3 Answers

Of course removing the converters will turn on the check engine light. The downstream O2 sensor(s) will see there is no functionality and trigger a catalyst inefficiency code.

As far as the battery is concerned have it load tested along with your alternator.

If your collision involved the front end it would likely have damaged the AC condenser. Aside from that, proper diagnosis of your AC system is needed as shown in one of Scotty's videos today.



Yeah obviously.

P0420 cat efficiency bellow threshold.

Together with probably other fun ones!


Yes, deleting the cats will turn on the CEL. You need to have the ECU tuned to turn off O2 sensor reporting to turn off the CEL.