Like many car owners facing engine performance issues and the dreaded check engine light, I started my troubleshooting journey with the OBD2 scanner. Two codes popped up on my 2004 Chevy Cavalier: P0172 (running rich) and P0420 (catalyst efficiency below threshold). Sound familiar? If you’re searching online, maybe even on YouTube, for “2004 chevy cavalier obd2 plug no power site youtube.com” trying to diagnose similar problems, you’re in the right place. While my OBD2 plug was working fine, leading me to these codes, the real issue was a bit of a rabbit hole, and I’m sharing my experience to hopefully help you out.
My initial thought, based on online forums and videos (like you might find on YouTube), was the MAP sensor. The P0172 code is often linked to MAP sensor failures causing a rich fuel mixture. Accessing the MAP sensor on the Cavalier isn’t the easiest task, but I decided to give it a shot before considering more drastic measures. I ordered a new MAP sensor, thinking this might be the quick fix.
However, things took a turn for the worse. Driving home, my Cavalier started losing power dramatically. I ended up limping along the shoulder with hazard lights on, barely able to reach 30MPH. Back home, a quick inspection under the hood revealed nothing obvious – no smoke, no burning smells, and the coils weren’t excessively hot. Another OBD2 scan confirmed the same P0172 and P0420 codes. Revving the engine was met with sputtering and a complete lack of power above what felt like 2000-3000 RPM.
Frustrated, I decided to try something a bit unorthodox based on a hunch. I disconnected the upstream oxygen sensor and started the engine again. The change was immediate and dramatic. The engine ran incredibly smoothly. (Important note: running your car with the O2 sensor disconnected, especially at high RPMs, is not recommended for extended periods and can be noisy!). Even with the hood closed, the newfound power was undeniable. I cautiously took it for a test drive up a nearby hill, and the car pulled with a force I hadn’t felt in ages. In third gear at 55MPH uphill, it wanted to accelerate even more.
This test pointed to a clogged catalytic converter. The faulty MAP sensor, by causing the engine to run rich for an extended period, had likely damaged or clogged the catalytic converter. Oddly, the converter wasn’t glowing red hot, which isn’t always an indicator of blockage.
So, while my initial search and code readings led me to the MAP sensor, the root cause, exacerbated by the faulty sensor, was the catalytic converter. I’ve ordered a new Magnaflow catalytic converter and will also replace the MAP sensor as originally planned.
If you’re experiencing similar issues with your 2004 Chevy Cavalier, especially if you’re seeing P0172 and P0420 codes, don’t immediately dismiss a clogged catalytic converter. While checking the MAP sensor is a good first step, consider the possibility of a restricted exhaust flow, especially if you’ve been experiencing rich running conditions. Hopefully, sharing this experience helps someone else avoid similar troubleshooting headaches and gets their Cavalier back on the road.
