[wwdwgs]

P0420 (insufficent cat. performance) code on and off.
I hijack this forum again, the problem is on CR-V with 190K miles.
This code appeared after filling up with gas on Gulf gas station. I doubt that that particular gas station uses 'top-tier" gas.
The scanner showed that the STFT and LTFT were too high - about 45-35% respectively. I cleared the code.
Then I filled up on my favorite station - the code didn't appear. The trims went to normal (in their teens).
Then, again, on nearly empty tank, I filled about 3 gallons (that was Turkey Hill station) and the light was on again.
Then, on nearly empty gas tank, I filled up on my other favorite station - the light was gone.

From the research I found that this P0420 code may be triggered by low quality gas (improper octane rating - an I assume by improper, they mean lower than 87), or by low fuel pressure (that causes high trims).

This had happened to me before a few years ago. So, now I can tell that the problem was (is) with the gas, therefore those questionable gas stations dilute the gas or sell low octane gas as higher (let's say they sell 85.5 as 87). Both of these questionable stations were in low-income, shitty, run down, not-so-clean neighborhoods.

 

[2011.2017.odyssey]

I only use shell gas for the fleet.

Got the P0420 code a month or so ago and ran a cup of acetone through a half tank of gas, did this procedure twice.

Had the old gal up in the air to do the strut rebuild last weekend, and noticed the flange bolts to the bank (1) cat where it joins the downpipe were disintegrated and hanging on by rust.

slight signs of exhaust escape around the flange but no noise, so heated up the rotted bolts air chiselled the rust off and tapped them out.

Replaced with new hardware.

I think this was the original cause of the P0420, with air getting in and throwing the readings off.

if you think your cat could be starting to go, acetone doesn't hurt with proper dilution.

There are some vidyas on loobtube that show removing the O2 sensor and getting a borescope/endoscope camera in the hole to see if the honeycomb element is coming apart.

a sure sign the cat is done and needs changing.

 

[WiiMaster]

You all get P0420 after filling up....meanwhile I've gotten P3400 immediately after filling up...

 

[wwdwgs]

WiiMaster, you are special!

 

[wwdwgs]

Update:
gas level went low (remaining 80 miles) and the light poped up again (same P0420).
I filled the tank with gas - the light was still on until the tank was low again.
I erased the code and filled up with gas. After 30 miles - no light.
I didn't check for short and long term fuel trims other that what was described above.

 

[wwdwgs]

Update:
full tank of fresh gas (at my favorite gas sta.) - no light. I drove until the tank is 99.9999% empty and added a couple of gallons of gas at Shell (!!!) sta. The CEL popped up immediately. I filled the tank up at another gas sta. the light is still on. Note: I use 87 octane gas (per Honda's recommendation).
STFT is in mid teens to 20-25%.
Sprayed with starting fluid on the intake, intake boot - no change in rpm's - no vacuum leak there.
If there is a vacuum leak in the system (after maf sensor), then the error code should come up right away. Am I correct in this assumption?
I will erase code and check for STFT again in a near future...

 

[wwdwgs]

Update:
1- Code erased. Checked for STFT and LTFT. STFT climbed from 0% to 25% in a few minutes. High PRM's lowered the STFT, then they came back.
2- Fresh tank of gas at Costco and 200-ish miles later code (P0420) came back.
3- Erased the code again.
4- Watched STFT/LTFT go from 0% to 27% again and within a few seconds (as shown on a video).
5- Sprayed the starting fluid to every part of intake (after MAF) that I could reach - no increase in PRM's = no air leaks.
6- Cleaned MAF with MAF cleaner - didn't help. I noted that MAF's wires have some dirt or deposits on the air filter side. The opposite sides are clean. Since there's no error code for MAF sensor, I didn't test it.

after all this "efforts" I think that:
1 - quality of gas is not the cause of this problem
2 - MAF sensor is not the cause, either.

I should check the following:
1 - the fuel pressure. I will check if Autozone or the like can rent a tester.
2 - probably, the downstream oxygen (O2) sensor (190K miles on it).
3 - look into the cat converter through the O2 sensor hole to check if it's in good shape (clean or not).

Regarding the oxygen sensors - I have a recording of live data of the primary (upstream) O2 sensor, which measures mA and the secondary (downstream), which measures V. YT videos usually show both O2 sensors with Volt measurements. I will post links for my videos later.

Note: the upstream O2 sensor is new (yes, Denso). PCV valve is also new (both 1 year old).

Question, what is the Intake Air Bypass Thermal Valve? This is 4-cyl CRV. Can this valve play a role in regulating air volume and cause "air leak" if it "breaks"? I understand that this valve is used for faster warm ups.
Also, If I'm not mistaken, the good live data for downstream O2 sensor should look like a comb - the volt values should jump up and down.

Videos: Live Data - STFT and LTFT; Live Data - O2 sensors.

 

[2011.2017.odyssey]

probably, the downstream oxygen (O2) sensor (190K miles on it).

Have you tested each O2 sensor?
Your foxwell graph isn't much help... the voltage data is captured with ECT1 at 158F and above running temp, and engine rpm at 3000 rpm without a load.
You should be seeing 1.27 volts, based on the above test conditions.

Heated O2 Sensors (HO2S) also have a 90k mile service life (right out of the crv service manual)
Anything after that is borrowed time.

Like mentioned before, why don't you take the cat O2 sensor out and get a borescope camera in there to look at the element.
Going to wager it's starting to come apart in pieces.

If the cat is not coming apart, then try a few applications of a cup of pure acetone in the half a tank of gas, that would be my next try.

Have done it on theody a total of 6 times now, no issues and no P420 anymore.
Original cats original O2 sensors at about 140k miles.
The O2 sensor heating elements are getting tired, she runs rich when cold but no codes.

 

[wwdwgs]

No, I didn't test O2 sensors. The upstream is 1 year old, the downstream is original (190K mi).
I will post an update in a near future.

 

[wwdwgs]

Update:
with the CEL still on, I filled up at Costco. The light was still on. After driving about 100 miles light is gone.
So.. If there was a vacuum leak, that leak won't fix itself.
If the fuel pressure was low, it, too, won't fix itself (especially in cold weather).
I think that the problem was with the quality of gas, compounded with "dirty" MAF sensor.
Now, I need to check STFT and LTFT and will update this post.

 

[wwdwgs]

Update (sad update):
STFT and LTFT are through the roof again - (coolant temp, stft, ltft, rmps):
190F, 21.9%, 4.7%, 800 rpms
180, 31.3, 0.8, 800,
176, 10.9, 2.3, 2 000
181, 7.8, 3.9, 2500
183, 7.8, 4.7, 3500
194, 25, 7, 700
I also wrote down some other stats:
AF FB (ST.FT) (I assume this is Air-fuel short term fuel trim) = 1.466 (what units???). IF this value is above 1, then it means "increased FI time". OK. I agree with this.
AF BA AVE (LT.ft) (I guess - long term fuel trims) = 1.264 (i don't know the meaning and significance of this value)

next: ari-fuel ratio: (type of sensor = value @ rpms)
AF sensor = 0.72mA @ 660, 0.016 mA @ 2000, 0.0094mA@ 3000
AF Lambda = 1.037@660, 0.993@2000, 0.098@3000 (ideal is, as I understand, 1.0)
AF fuel raito = 15.3@660, 14.5@200, 14.5@3000 (ideal 14.7??)
AF Lambda CMD = 0.98@660, 0.99@200, 0.996@3000 (ideal should be 1.0??)
HO2 S2 sensor (I assume - downstream O2 sensor) = 0.39V@660, 0.7-0.63V@2000, 0.45-0..69V@3000 (it seems ok to me)

My next steps would be:
1 - check fuel pressure (autozone lends fuel pressure test kits)
2 - inspect spark plugs and cylinders with borescope
3 - pull out fuel injectors and see how they spray
4 - unscrew downstream O2 sensor and inspect the cat converter internals
5 - I did measure the cats temperature last year. I don't remember the values, but the outlet of the cat was hotter that inlet. I also saw the cat temp using the scan tool, but don't remember the exact numbers
6 - pinch all vacuum lines one by one and see if that would help to lower STFT. There is also an Air Bypass Thermal Valve that allows more air into the cylinders when engine is cold
7 - cup of acetone, as mentioned above.
8 - have my favorite drink

 

[2011.2017.odyssey]

you think any of this could be gremlins coming back to haunt from the head gasket job?

 

[wwdwgs]

I don't know. Do you think I screwed up and the air is seeping thru the gaskets (either head, or intake)? I didn't get P0420 code immediately after the HG job. About half a year had passed between this job and current problem my car has. Assuming that I didn't have this problem for a long time, even prior to the HG job.
Intake manifold on this 4-cyl engine is in front and I could only spray (the starting fluid) at the top and sides, the bottom was impossible to reach (with that spray can).
I din't even think that I would need to check STFT and LTFT after the head gasket job. I don't have any records of fuel trims.
What I can do is to review the old pictures of live data that I took a year ago, and even earlier, and see if there is any of then that show the fuel trims.
now, I'm going to have nightmares, thinking about what if the problem originated a long time ago.

 

[wwdwgs]

Update:
No test were performed. With current conditions, I filled with gas again. The light stays on. Drove about 150-170 miles (in a week), the light turned off for and came back in about 60-70 miles during normal suburban driving.
The new code is P0171 - fuel system too lean.
Observation - in the last couple of months the gas mileage lowered about 2-3 mpg., which is, partially, due to smaller tire size.
The can tool gives me possible causes for this code:
1 - vacuum leaks - possible somewhere...I'll have to check every hose again...
2 - improper valve adjustment - NO
3 - faulty injectors - could be - didn't check them yet, I'll check them with fuel pressure test.
4 - clogged air filter - NO
5 - faulty fuel pump or fuel pressure regulator - the fuel pressure test will tell, which was not done yet
6 - faulty evap canister purge valve - i don't know
7 - faulty A/F sensor (sensor 1) - that translates to upstream oxygen sensor, which is 1 year old, so, probably - NO

I'll take a little pause on diagnostic work and will update in a near future...

 

[wwdwgs]

Update:
CEL was not reset.
no test were done yet.
I filled up with fresh gas (Costco), the light turned itself off. Used up all gas and filled up again (other gas sta), drove 10 miles - no light.
I didn't check for error codes yet. Will do that tomorrow-ish.
This behavior bothers me.. I honestly suspect bad gas.

 

[jiantao]

It might not have anything to do with gas, and it's something completely different. Maybe the cat or O2 sensor, as you mentioned.

Here's my experience with P0420 on my Camry:
2017, around 135K miles - CEL comes on, P0420. Cleared the code, stayed off for awhile. Took to inspection at 137K, passed, good sticker for 2 years.
2018 around 138K, CEL comes back, erased code, comes back months some later around 140K.
2019 around 147K, due for 2 year inspection again so erased code, drove for a little bit, passed inspection. Shortly after, CEL back again. Now the code says oxygen sensor (it was P0420 - catalytic converter for years).
2021 around 155K, due for inspection again but this time clearing the codes doesn't work. CEL comes back before the readiness monitors reset. Replaced the offending oxygen sensor which is causing the CEL (I think it was P0136). FIXED - CEL does not come back.
Fast forward to 2024, around 175K, the CEL is back again and is once again P0420 (7 years after it first came on). Developed an exhaust leak about a week after the light came on this time, not sure if it's related or not. I've tried clearing it a few times since and it always comes back. At 178K now.

Going to try cataclean next.

 

[2011.2017.odyssey]

It might be temperature related, you posted this in October its now February.

Maybe the colder months might be masking this isue?

Inversely my old g2 ody the p420 would come on in the colder months not warmer, when it would run rich at cold start.
would clear the light and it wouldn't come back until the next winter.

 

[wwdwgs]

light and it wouldn't come back until the next winter.

Hm...

 

[wwdwgs]

Update:
I just started the car, and smelled the exhaust gas - it smelled like unburnt gas. When engine is at operating temp. the exhaust gas has no smell.
The STFT and LTFT are at their high - 25 and 33 percent respectively.
Error codes are: P0420 and P0171 (fuel system too lean, faulty fuel pump/regulator (pressure), faulty EVAP canister purge valve, faulty injectors, clogged fuel filter, improper valve clearance, vacuum leaks).
After cleaning the codes, STFT and LTFT went up 22% and 0% in 30 seconds and, in 2 minutes, got to 20% and 2%.
I guess, I must fix something after all and stop blaming on gas quality.

 

[wwdwgs]

Update:
Checked the fuel pressure: almost 60 psi when priming, 42 psi after priming. repeated 4 times - same result. I tried one more time and the resting pressure started to drop.
Pulled out the FI rail (to check if they leak - but my car doesn't show any signs of leaking FI), but couldn't repeat the test - I heard the clicking sound and not pump - so, no pressure.
The normal pressure range for this CRV is 44-57 psi.
Verdict: for now, I think that the pressure regulator (located probably by the fuel pump) is faulty.