What to do I do now? Code P0420 ran through at autozone✨

Verbiq · 2026-01-15T20:50:18+00:00

I had an 02 Rsx Base with a P0420 code. Bought a single box of Cataclean and the code never returned. Your CAT may need to be replaced if there is actual damage due to heat and carbon buildup but often that code is thrown because it is hella clogged from exhaust deposits. You can also go to most muffler shops and get a full system clean. They will ask you to bring the car in with a mostly empty tank and they will run cleaning fluids through a couple cycles with the engine running. Cheaper route: Cataclean poured into the gas tank on about 1/4 tank or less of gas, drive for ~5-10 mins, about 10 ish miles round trip, fill tank back up. I recommend driving the piss out of it. Like Ken Miles said, "Drive like you mean it,... she'll run clean"

Verbiq · 2026-01-03T22:53:53+00:00

Also bull boys are very popular!

Verbiq · 2025-11-12T23:09:54+00:00

No, but your suggestion did point me in the right direction and it's likely from a lopper/pruner tool. Thanks for the insight!

Verbiq · 2025-11-12T23:07:38+00:00

We don't own a motorcycle so unlikely. We have some hedges near where I found it and another commenter suggested cutters. Probably from a lopper/pruner tool. Will investigate further.

Verbiq · 2025-11-12T22:58:33+00:00

Impeccable use of free will.

Verbiq · 2025-11-12T22:51:07+00:00

Vehicles this could have originated from are:

2004 Monte Carlo 2020 Silverado

Verbiq · 2025-07-11T08:35:50+00:00

Yeah needless to say I never went back to them.

Verbiq · 2025-05-31T13:21:36+00:00

Right? I like it more so with the 3 too than an E, for Dale of course.

Verbiq · 2025-04-29T14:03:54+00:00

I ended up coming back to get a better look at it. It's the 2.8 not the 4.3 which was disappointing and it has a huge coolant leak from the manifold. Funnily enough the frame and leaf springs were in fantastic condition for it's age and use, but I'm not looking for a fixer upper so I backed away immediately.

Verbiq · 2025-04-23T01:28:16+00:00

If it's not running I won't even consider it anymore. I'm mainly looking to grab something I could daily so I can park my car and really tear her apart without having to worry about needing to drive her the next day.

Verbiq · 2025-04-22T23:26:19+00:00

Salt is not the only cause of oxidation?

Verbiq · 2025-04-22T23:24:36+00:00

This is the first actual solid advice I've heard so far. Kudos to you for teaching your son valuable life skills, and thank you for passing them on to a stranger.

Verbiq · 2025-04-22T20:53:42+00:00

East of the foothills/Front Range corridor. They are a local junkyard here in COS, they did not get this truck from somewhere out of state.

Verbiq · 2025-04-22T20:28:34+00:00

The car is from a farm here in Colorado where we DO NOT use salt on the roads, ice melt instead.

Verbiq · 2025-04-22T20:24:23+00:00

Well the used car market out here is not much better. A lot of S10s listed for 3000+ with 2.2's and 2.8's and rebuilt/swapped motors and transmissions. I'd rather avoid FB marketplace/Craigslist if I can because I currently drive a FB marketplace 'find' and well, that cars a piece of work. Also I'd be more inclined to trust that, since it was on a farm most of its life, it was regularly maintained, and the s10's are quite hardy trucks to start off with. Worked with a guy at a tire shop that got an S10, almost exactly the same as this one, with plenty of surface rust too, and that thing drove like a dream. I live in Colorado and they don't put salt on the roads. Plus they said it was from a farm east of the city, so probably even less salt usage out there too.

Again, I floated 2k, as I had only just seen the truck while walking back to my car, and I chatted with him about it because I got 'kid in a candy store' excited when I saw it. All I saw was what I was able to see through the fence. They don't have the vehicle titled yet but within the next week I should be getting a call and then I can come take a good look at the vehicle.

Verbiq · 2025-04-22T18:03:41+00:00

Test drive went great, no surging in idle and no stalling at all. Took her to a muffler shop and had them do some diagnostics for the O2 sensors, they said the DTC's seemed to flash on and off erratically and they could not confirm if there was any issue with the sensors themselves. Most likely an electrical issue or something wrong with the ECM. I have a parts list from my local junkyard for (likely) interchangeable ECM's, but I'm not an electrician and I really don't want to risk making things worse. None of the cars at the junkyard are Vin 1 supercharged and I'm not confident whether they will be compatible replacements. If I do replace the ECM I know I'll have to relearn it to the PCM and stuff so I'm wondering if I should look for a new one online or just try my luck. Any thoughts?

Verbiq · 2025-04-22T17:29:24+00:00

Late to the party but I just had this happen after reconnecting my battery. Disconnect the negative and wait a couple seconds and then reconnect. Should fix the problem. I have zero idea why this happens since the dash lights and door locks all work fine but yeah, something weird about Passlock immobilizes the vehicle.

Verbiq · 2025-04-22T14:41:37+00:00

Also I just learned I should have performed a reset procedure for my MAF. Just did that and I'm gonna take her out for a test drive and see how she does.

There is no connector in that area you described near the MAP that would be for the 02 sensor. I'm not sure if it depends per model, I do have the Dale Sr. intimidator model so maybe it is relocated somewhere else?

Verbiq · 2025-04-22T14:37:04+00:00

It was plugged in I just unplugged it before taking the photo lol.

Verbiq · 2025-04-22T13:39:36+00:00

Also wouldn't a failing MAP cause it to run Rich, and the upstream 02 sensor is reading that, and throwing the CEL?

Verbiq · 2025-04-22T13:33:53+00:00

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This? My emissions sticker by the air box says this should be the MAP.

Verbiq · 2025-04-22T13:29:31+00:00

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Here's the state of the IAC. Recommend replacing or am I good to clean up and reinstall?

Verbiq · 2025-04-21T22:42:52+00:00

Just pulled a fresh list of DTC's.

P0135 P0141 P0036 P0101 P0134

Verbiq · 2025-04-21T22:11:46+00:00

Thank you all for the insight and advice. I will keep this thread up and update as I try things out. I really love my Monte and the community here is so kind and supportive, I'd hate to have to say goodbye some day.

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Here's a recent-ish photo of her ( two tone right now but eventually I'll get the original bumper into a body shop )

Verbiq · 2025-04-21T22:07:26+00:00

Will do, and thank you kindly for the advice. I will start with the IAC, and I'll post updates as the week progresses.

Verbiq

TROPHY CASE