Motor Vehicle Maintenance & Repair Stack Exchange
Motor Vehicle Maintenance & Repair Stack Exchange

Questions tagged [p0420]

An OBDII fault code for Catalyst System Low Efficiency

This code specifically relates the bank 1 catalyst. Related similar fault codes are available for catalytic converter in different locations in the exhaust system. Such as P0430 for the bank two converter.

Chevrolet - Catalyst System Low Efficiency Bank 1

Lexus - Catalyst System Efficiency Below Threshold (Bank 1)

Saturn - Catalyst System Low Efficiency

40 questions
13
votes
3 answers

2005 Dodge Ram: Easy way to diagnose code P0420?

My truck is reporting a code P0420, which apparently is "Catalyst System Efficiency Below Threshold (Bank 1)" which can either be the catalytic converter or the rear O2 sensor. The code came on at about 30k miles, so I doubt it's the converter. So…
dave thieben
  • 595
  • 1
  • 6
  • 10
12
votes
3 answers

Check Engine code P0420 Catalyst efficiency below threshold bank 1

After months of normal driving with no problems, my 2003 Honda Civic EX check engine light came on during a long trip. Got it scanned and it's P0420: Catalyst efficiency below threshold bank 1. They said it could be a bad catalytic converter or…
endolith
  • 1,347
  • 8
  • 24
  • 42
9
votes
1 answer

Why does the Check Engine code for emissions failure disable traction control and cruise?

I have a 2010 Forester with nearly 100k miles, and it just started giving the "emissions" check engine code (P0420, Catalytic Converter Efficiency Below Threshold). When that code is tripped in the system, it responds by flashing 'cruise' and…
Joe
  • 285
  • 2
  • 7
7
votes
3 answers

my 2011 Chevy Equinox check engine light on, reads code P0420

Check engine light been on. I checked gas cap the other day and it stayed on. I will put premium fuel in next time i fill up. It's been on for about a week. Any ideas to cause or solution?
steve
  • 71
  • 1
  • 1
  • 2
7
votes
1 answer

Erratic single fault code: P0420, P0440, P0446. Normal variance, or indicative of something deeper?

Working on diagnosing an evap/emission/fuel system problem on my Toyota 2003 Corolla. More on that in this question. On 3/2, I saw a mechanic use his handheld OBD to read a code P0420. On 3/12, without any code resets, I got my Ozzy OBD reader and…
bishop
  • 871
  • 1
  • 9
  • 23
7
votes
3 answers

2003 Toyota Corolla, 185k: erratic OBD codes, fuel smell, other symptoms

TL;DR: O2 sensor data, thermal measurements, and physical resonance tests all point to a failed Catalytic converter. Here's the back story. MIL illuminated with codes P0440, P0420, P0404. Around this time, I noticed a gentle mechanical…
bishop
  • 871
  • 1
  • 9
  • 23
5
votes
1 answer

How could the code point to a faulty cat, when the O2 signals are normal?

I'm getting code P0420 on an '03 Vibe. The rule of thumb is that this means the catalytic converter is gone. Yet the pre- and post- cat O2 signals appear to indicate that the cat is doing its job. Unfortunately Toyota/GM have designed the entire…
Calaf
  • 1,565
  • 7
  • 21
  • 32
5
votes
1 answer

1998 Honda Civic - O2 sensor or catalyst failure?

I have the P0420 code on my 1998 Honda Civic DX (catalyst system efficiency below threshold bank 1). I want to be able to properly diagnose the problem myself without just throwing new parts at it. A new catalyst is fairly expensive. I used a scan…
Robert Stiffler
  • 222
  • 3
  • 7
5
votes
3 answers

What would cause a car to lose power a few seconds after starting, then run normally?

I start my 2003 Honda Civic each morning and drive to work. A few hundred feet down the road, the engine will sometimes behave as though it is running out of gas and lose power momentarily. It doesn't completely stall, I ignore it or pump the gas,…
endolith
  • 1,347
  • 8
  • 24
  • 42
4
votes
0 answers

Nagging P0430 (and now a pending P0420 too!) 2004 Lexus ES330

I've got a 2004 ES330 (2nd owner) with roughly 315,000. We didn't pay much for the car in 2012 with 164,000 miles. So, i've never gone overboard in maintenance of it. A year ago, when it was time for 2017 annual emissions testing, I had a persistent…
MJBeaten
  • 41
  • 3
4
votes
2 answers

Can a loose radiator cap cause P0420?

The other day, I loosened my radiator cap and forgot to re-lock it. About 10 mins into my drive home, my CEL came on (and about 2 mins later, I went "DOH!") The code is the always super helpful and easy to chase P0420. I read that one of the…
bbadgett
  • 43
  • 1
  • 4
4
votes
2 answers

Does P0420 on a Vibe result from a pre- or a post- O2 sensor?

My CEL is on and the code reads P0420 on a 2003 Vibe. There are apparently three options: Pre-cat O2 sensor Post-cat O2 sensor CAT model 51274 This is most likely beyond my mechanical abilities (been bitten), but I'd like to get the part from a…
Calaf
  • 1,565
  • 7
  • 21
  • 32
4
votes
3 answers

P0420 in a Prius

EDIT #2: I rescanned, looking at the correct data, and found the rear O2 sensor was definitely bouncing up and down with the forward sensor's lambda reading. Since I have looked for leaks and couldn't find any, I decided to just go for a new…
Bob
  • 271
  • 1
  • 4
  • 10
3
votes
3 answers

06 Chevy Cobalt ls 2.2 l . Replaced B1S1 O2 sensor still having issues

I went and had my 06 Cobalt checked out because the dreeded check engine light came one and I got the P0420 threshold bank 1 code. My mechanic, who has been a good friend of mine for quite some time, told me I needed to replace my B1S1 sensor from…
John-Felipe
  • 31
  • 1
  • 1
  • 2
3
votes
1 answer

Should I replace my Catalytic converter?

My 2007 Xterra had the P0420 code pop on. My understanding is that it most likely that the Catalytic converter is going out. If this is the case, how high of a priority is it to fix? Before you answer, let me give you some insight. The truck is…
junta
  • 133
  • 3
1
2 3