Questions tagged [p0420]

An OBD11 fault code for Catalyst System Low Efficiency

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33k views

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 ...
11
votes
3answers
103k views

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 ...
5
votes
3answers
59k views

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'...
7
votes
1answer
2k views

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, ...
7
votes
3answers
2k views

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 ...
4
votes
1answer
2k views

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 ...