Cavox Research Team · case log
P0420 on Toyota & Scion: the cases behind the evidence
What this page is
2,509 content rows captured before deduplication
204 page, post, video, SERP, article, or official-record rows + 2,305 individual comment rows. Every comment is counted as one content row.
At least 2,489 unique content units
188 unique source documents + 2,301 unique comments. 20 repeated captures or appearances were removed; the same comment or page is never counted twice.
Unique units by source channel
- Forums: 38 units · documents: 38
- Independent articles: 4 units · documents: 4
- Official records: 38 units · documents: 38
- Reddit: 995 units · documents: 82 · comments: 913
- SERP results: 17 units · documents: 17
- YouTube: 1,405 units · documents: 17 · comments: 1,388
A source can appear in more than one channel. The channel totals below overlap by 8 documents; the unique total above removes that overlap.
134 owner discussions reviewed · 130 had readable outcome evidence
116 still did not name a confirmed final repair, so a temporarily cleared light was not treated as proof.
16 public community cases + 12 separate federal records
Community rows passed the public quote, URL, and case-role checks. Federal complaints remain a separate counted lane.
This is a lower bound: forum captures retained as whole-thread documents are not yet split into individual replies, and comments were not fetched for every discovery candidate.
Inclusion rule
Federal: every NHTSA complaint whose narrative names P0420 on Toyota or Scion vehicles — the complete set at pull time, nothing sampled.
Community: every admitted record is either an owner account or a documented repair case for one Toyota or Scion vehicle with P0420; it has an immutable raw receipt, exact source excerpt, and public HTTPS verification link. General explainers, sources behind login or a paywall, and sources without a substantive verbatim excerpt stay out of this public layer. Counting rules: /methodology.
ODI-11235071 · filed 2019-07-26 · 75,445 mi
“I HAD THE J02 RECALL PERFORMED ON FROM FEBRUARY 8TH-13TH. 1200 MILES AFTER J02 RECALL CAR RUNS SLUGGISH GOING UP CANYON. STOP CAR AND ENGINE IS MISFIRING.…”
ODI-10550051 · filed 2013-10-29 · 191,187 mi
“WHILE DRIVING HOME ON 9/24/13 MY CHECK ENGINE LIGHT CAME ON, I DROVE RIGHT TO THE TOYOTA DEALERSHIP. I WAS INFORMED THAT THE CATALYTIC CONVERTER SYSTEM WAS…”
ODI-10735783 · filed 2015-07-22 · 244,309 mi
“7/14/2015. EVAP SYSTEM. CHECK ENGINE CODE P0446. CANNISTER CLOGGED AND VSV AND PURGE VALVES LEAKING. REPLACED CHARCOAL CANISTER. MILEAGE:…”
ODI-11659073 · filed 2025-05-05 · mileage not stated
“ALL OF A SUDDEN, ALL OF MY WARNING LIGHTS CAME ON INCLUDING: BRAKE LIGHT, CHECK VCS SYSTEM, ABS, ALL OF THE EXCLAMATION LIGHTS, ETC.. IVE BEEN VERY DILIGENT…”
ODI-10639515 · filed 2014-09-27 · 185,000 mi
“ALL TOYOTAS WITH 2AZFE ENGINES AND THEIR VARIANTS NEED TO BE RECALLED. THERE IS AN INHERENT PROBLEM WITH EXCESSIVE OIL CONSUMPTION DUE TO A DESIGN FLAW IN BOTH…”
ODI-11596407 · filed 2024-06-25 · mileage not stated
“Unknown - The airbag light has been on for a while. Check engine light is also on, and after a few repairs/replacements of diagnosed issues the light remains.…”
ODI-10251467 · filed 2008-12-11 · 87,000 mi
“MY 2004 TOYOTA MATRIX AT 87,000 NOW NEEDS A NEW CATALYTIC CONVERTER. THE CHECK ENGINE LIGHT CAME ON AND I TOOK IT IN TO BE DIAGNOSED. P0420 WAS THE CODE.…”
ODI-10359074 · filed 2010-10-04 · 127,000 mi
“2001 TOYOTA RAV4 ECM AND TRANSMISSION REPLACED IN MAY OF 2009. PAID OUT OF POCKET. REPLACEMENT WAS A REBUILT TRANSMISSION INSTALLED BY DEALER (VICTORY TOYOTA…”
ODI-10863990 · filed 2016-05-09 · 167,000 mi
“HELLO, I HAVE A 2003 TOYOTA SEQUIOA WHERE THE ENGINE LIGHT AND THE VCS LIGHTS ARE BOTH ON. I SAW ON YOUR PAGE SOME REALLY HELPFUL INFORMATION ON THIS…”
ODI-11718059 · filed 2026-02-15 · mileage not stated
“Dear Sir, On April 2026, I need to do the semiannual smog check. Right now, I face DTC P0420 error code and I can't pass the smog check inspection. Note that I…”
ODI-10850705 · filed 2016-03-21 · 128,000 mi
“TOYOTA TACOMA LIMITED SERVICE CAMPAIGN. I DROPPED MY TRUCK OFF IN NOVEMBER 2015 FOR A FRAME INSPECTION, I WAS THEN TOLD I COULD NOT DRIVE MY TRUCK OFF OF THE…”
ODI-11292428 · filed 2020-01-01 · 94,000 mi
“CHECK ENGINE LIGHT: P0420 FAULT CODE. ALSO, THERE IS A RATTLING SOUND AND EXHAUST BACK UP TO THE PRESSURE RELEASE MOUNT WHERE THE EXHAUST CONNECTS TO THE…”
posted — · mileage not stated
“So...he changed the coil pack, and it's all good now!”
Symptoms stated: check engine light came on
Cost cited: $400
Thread status: a resolution was reported in the thread
Outcome words: “So...he changed the coil pack, and it's all good now!”
posted — · mileage not stated
“Hello, I recently purchased a 2007 4runner SR5, V6 with about 180,000 miles. This is my first 4Runner and I like it a lot. But I'm also getting some DTC codes…”
Symptoms stated: P0420 code; P0430 code
Attempts mentioned: dealer replaced Bank 1 O2 sensor 2
Thread status: no verified final outcome was posted
posted — · 282 mi
“My 282k miles 2006 Toyota Prius is throwing code P0420 and I want to check what could be the culprit. Indeed changing the catalytic converter probably will…”
Symptoms stated: P0420 code
Thread status: no verified final outcome was posted
posted — · 35 mi
“So I went on ebay and found a company from Canada (First Choice Exhausts). Their 2nd Generation cat went for $108, plus $9.99 shipping and freaking 8% tax for…”
Cost cited: $128
Thread status: the attempted repair did not hold
Outcome words: “So I went on ebay and found a company from Canada (First Choice Exhausts). Their 2nd Generation cat went for $108, plus $9.99 shipping and freaking 8% tax for”
posted 2023-07-02 · mileage not stated
“O2 sensor was replaced (code went away) and drove the car for a month no code. Now all the sudden the code has come back”
Thread status: the attempted repair did not hold
Outcome words: “O2 sensor was replaced (code went away) and drove the car for a month no code. Now all the sudden the code has come back”
posted 2024-09-28 · mileage not stated
“I have a 2002 Toyota Sequoia that has had a P0420 for about 6 months. The radiator cracked and started smoking about 1 year ago. It had a bad misfire right…”
Symptoms stated: bad misfire
Thread status: no verified final outcome was posted
posted 2025-04-17 · mileage not stated
“Our 2011 Toyota Matrix with the 1.8L with over 300,000km or 182,000 miles. It's been giving us some issues starting and rough idle. It gave us a P0300 code so…”
Symptoms stated: rough idle; P0300 code; P0301 code; P0302 code; P0420 code
Attempts mentioned: Replaced plugs
Thread status: no verified final outcome was posted
posted 2025-08-23 · mileage not stated
“I had a P0420 code show up on my 2003 Toyota corolla. I checked the live data using a obd scanner to see if its the oxygen sensors. The bank1 sensor1 were…”
Symptoms stated: P0420 code
Thread status: no verified final outcome was posted
posted 2026-02-28 · 240 mi
“Hello, I have a code for the catalytic converter p0420 and p2423 (Toyota hcac). I know the cat is probably bad but I want to make sure before buying a new…”
Symptoms stated: 240k miles
Thread status: no verified final outcome was posted
posted 2014-11-04 · mileage not stated
“2004 Toyota Prius. We had the check engine light come on. Took it to the shop to get the codes read. The code was "P0420 - Catalyst System Efficiency Below…”
Symptoms stated: no other outward symptoms
Thread status: no verified final outcome was posted
posted 2015-11-21 · 230 mi
“A couple of weeks back, after getting a P0141 code (this was the only code at the time), I replaced the oxygen sensor on my 2003 Toyota Matrix. I drove it for…”
Thread status: no verified final outcome was posted
posted 2017-07-25 · mileage not stated
“Hello, I'm trying to test my vehicle for faulty o2 sensors before thinking of replacing the catalytic converter. I rev the warmed up engine at 2,500 rpm for 20…”
Thread status: no verified final outcome was posted
posted 2021-02-22 · mileage not stated
“I have a 2003 Toyota Matrix XR. She is throwing a P0420 code when scanned. The cat is not clogged...she accelerates just fine and loses no power going up…”
Symptoms stated: P0420 code
Thread status: no verified final outcome was posted
posted 2021-04-26 · mileage not stated
“Back again with this car that refuses to be happy. First I had a P2238 error, and replaced the Bank 1 Sensor 1 O2 sensor. Then I had a P0174 code, and turns…”
Symptoms stated: P0420 code
Thread status: no verified final outcome was posted
posted 2022-06-06 · 150 mi
“I have a Toyota Prius 2007 model and I got a check engine light recently. Went to autoZone and the dude diagnosed it as a P0420 code, which is related to a bad…”
Symptoms stated: check engine light; P0420 code
Thread status: no verified final outcome was posted
posted — · mileage not stated
“Hello all- Posted this under the Gen 3 & 4 forums accidentally, sorry for the redundancy, but wanted to get it in the right forum. Just last night, my 2003…”
Thread status: no verified final outcome was posted
Signal tags & bias
Signal tags are machine-applied with a code-specific, versioned wordlist (v1.0). In the federal lane: converter / catalyst named 8 · cost named 3 · exhaust leak / gasket 0 · inspection / readiness 5 · misfire / flashing light 2 · oxygen sensor named 1. The same chips orient community records but are not counted there. Quoted excerpts are checked against immutable source receipts. Structured symptom and attempt lines render only when the exact phrase is also present in that receipt.
Federal bias: federal complaints are self-selected — owners file when a problem is expensive, unresolved, or felt as a safety issue, so this set skews toward bad outcomes and says nothing about how often the code sets in the first place. Implausible odometer entries are kept verbatim; they are treated as possible typos in prose, never silently corrected.
Community bias: public discussion records are self-selected — they are richer on what was tried, what reportedly changed, and what it cost than on incidence. A record can be an owner account or a documented repair case; neither proves fleet prevalence.. Threads can disappear; when an archive snapshot exists the row links to it, otherwise it is marked live-only.
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