Cat codes in cold weather

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I just got my 211K mile Honda Pilot back from my trusted local independent mechanic last week. Had timing belt, water pump, and tensioner done, plus spark plugs and valve adjustment. Valve adjustment was more labor than the timing belt, since the intake manifold comes off. Also had him throw on an ATF Temperature Sensor on the transmission, since it shifted late/high RPM when cold, and sometimes ignored 4th and 5th altogether until warmed-up. That was another hour due to: two engine mounts and pull a coolant line. Well the good news, purrs like a kitten, lifter tap sound is gone, and the temp sensor fixed the cold shift problem. So-So news is same fuel economy. The scare came near the end of running morning chores, involving one medium-short and 2 short trips, I got a CEL. Stopped in at my mechanic who was just opening shop, he read codes P0420 and P0430, and then cleared them, said come back if they come back. No other codes. Since then I've been reading up on these codes. Here's what I (think I've) learned. They mean front and rear Cat performance under par. It takes two failed runs in a row to throw the code. They happen more often in cold weather. They usually don't mean the sensors are bad, since the before-cat and after-cat O2 sensors have to agree in lock-step that the same amount of oxygen is going by. Usually these codes mean it is time for new Cats. Can be caused by intake leaks and diagnosed by fuel trims. Some more info: These short trips occurred in 5F-9F morning weather. The Cats are missing their Heat Shields, because they 1/2 rusted off and the flapping, buzzing remains were removed. Codes have not come back (yet). Vehicle is well-maintained and does not have any fuel delivery issues. I throw in a bottle of PAO injector cleaner twice a year. Vehicle did consume a few quarts of oil for about 30K last year until I figured it out and replaced the clogged PCV valve. Current oil consumption is about 1/2 quart per 7500 OCI. My thinking Working hypothesis #1- short trips, crazy cold and no heat shields mean Cats never got up to operating temp twice in a row when it moved from Open To Closed loop. Working hypothesis #2- My mechanic, while awesome is only human, and left an intake leak when he replaced the manifold (he did use new gaskets) Working hypothese #3- Cats are going bad. Obviously I am rooting for #1. I do have a cheap BAFX ELM327 and Torque, but I've heard there is a procedure to check fuel trims, it's not just done at idle in the driveway? What would be the easiest way to check this? Any other easy diagnostics? (that is, not pulling the exhaust and looking up the pipes). Any flaws in my reasoning, or other hypothesis?
 
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cold could be a factor as my new to me 2011 frontier with 20,xxx on it threw that code during a cold spell. i cleared it with my actron scanner + its not returned in 500 miles.my cats are there with before + after sensors but i installed a higher flowing cat back system, so chalking it up to extreme Pa cold!!
 
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I check my FT's at idle, HVAC off, with car warmed up and in closed loop. If they are high at idle (>10%), but revving to 2500 RPM or so brings them down a good bit, then you likely have a vacuum leak. You have an old car with what I presume are the original cats. Could just be a fluke cold weather occurrence. I personally wouldn't worry unless it happens again in warmer temps. Then, I'd change out the O2 sensors and see if that fixes it.
 

HangFire

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Correct, 2005 Pilot. Thanks. There's a lot of debate on just changing out O2 sensors when there are no sensor codes. Of course, since I'm of the opinion they should be changed out with the Cat, it wouldn't hurt to do them first, and see what happens. If it comes back, of course. I'll start playing with Torque this afternoon.
 
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Newer cars since the 1990s use heated O2 sensors and most will use an upstream wideband heated O2 sensor(AKA AFS) and the catalyst monitor is looking at the waveform of the HO2S signal downstream from the main O2/AFS to see if the cat has lit off and doing its job. It doesn't take too much to take out a cat - a misfire event or any ignition/fuel system issue that dumps raw fuel into the exhaust or spikes the EGTs up is all it takes. You can access fuel trim as live data on Torque with a ELM327. But if you really want to see if the AFS/O2 sensors are up to snuff, you really need a oscilloscope, the Honda HDS and a compatible VIM, or a high-end graphing scanner.
 

HangFire

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Originally Posted by mclasser
I check my FT's at idle, HVAC off, with car warmed up and in closed loop. If they are high at idle (>10%), but revving to 2500 RPM or so brings them down a good bit, then you likely have a vacuum leak. You have an old car with what I presume are the original cats. Could just be a fluke cold weather occurrence. I personally wouldn't worry unless it happens again in warmer temps. Then, I'd change out the O2 sensors and see if that fixes it.
Yes. original cats. I just did this test with a fully warmed-up engine and A/C off. The two short-term fuel trims were right around 10% at idle, at a steady 2500RPM they bounce and then settle down right around 10% again. After running at 2500 RPM (no load) for a couple of minutes ~10%. I dropped back to idle again, then idle trims were 15% then after a minute it settled down to 10% again, and stayed there.
 
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Originally Posted by slacktide_bitog
You should replace the o2 sensors when replacing the car anyway smile
*cat not car, sorry for the typo
 

HangFire

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Originally Posted by slacktide_bitog
Originally Posted by slacktide_bitog
You should replace the o2 sensors when replacing the car anyway smile
*cat not car, sorry for the typo
Absolutely, if I ever do need to replace the cats, I will also replace the before and after o2 sensors on both. And thanks for the correction, I was ignoring it as I thought it was a snide remark about my old car.
 
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Originally Posted by HangFire
Originally Posted by slacktide_bitog
Originally Posted by slacktide_bitog
You should replace the o2 sensors when replacing the car anyway smile
*cat not car, sorry for the typo
Absolutely, if I ever do need to replace the cats, I will also replace the before and after o2 sensors on both. And thanks for the correction, I was ignoring it as I thought it was a snide remark about my old car.
Yeah, I just spotted the typo when I made that correction! ontome
 
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Originally Posted by HangFire
Correct, 2005 Pilot. Thanks. There's a lot of debate on just changing out O2 sensors when there are no sensor codes. Of course, since I'm of the opinion they should be changed out with the Cat, it wouldn't hurt to do them first, and see what happens. If it comes back, of course. I'll start playing with Torque this afternoon.
This. Far cheaper to try first if headed that direction anyway.
 
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replacing the cats should be a last resort as they are $$$$, if your ride is older + you can afford it dump it after clearing codes as cat-s can run from 1 to 3G installed especially in bigger hi zoot areas!!
 
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ON, Canada eh?
I was at my uncles on the weekend (dad's brother) and they have a Nissan Pathfinder (late 2000's) and my aunt was telling us that her check engine light was coming on only on really cold days. It's storing codes for the catalyst being below efficiency for both banks. We are going to investigate further once it's a little warmer. Just thought I would add to the discussion. I'll let you know how it turns out. Hers only has about 160,000km on it (100,000 miles)
 

HangFire

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No recurrences so far. While no Cats last forever, I'm thinking this was just a failure for them to light off in the extreme cold weather.
 
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