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Discussion Starter #1
I just bought the car, so do not know if there are mpg issues or anything like that. It has 203K on it, and it doesn't look like the previous owner was too much into preventive maintenance like replacing parts without codes.

Here's what I have so far:
The Codes:
P0420: Rear bank catalyst efficiency issue. Lexus tech in another thread says 99% of time, this code is a short in the O2 sensor heating circuit. New sensors are $100 for front and $30 for rear, so $260 for whole set.
p0443: Evaporative Emission Control System Purge Control Valve Circuit Malfunction (new valve is $50 to $100). Could also pull valve and test to see if valve and hoses hold vacuum.
p0497: EVAP System Low Purge Flow. I read somewhere that this could be due to dirt in hose from canister

I'm waiting for a friend who is a shade tree mechanic to take a look at it and narrow down the possibilities, but I wanted to know what you guys thought. From my experience, cars tend to develop similar issues, so other's experience is helpful.

My gut feeling was to replace all O2 sensors, since they probably need it anyway. On the other hand, I hooked up my odb2 dongle and looked for o2 sensors with torque app. The downstream O2 sensors moved between 0.3 and 0.6 or so over a period of 10 seconds or so. They were not real steady, but did not bounce around quickly like they might with functioning O2 sensors and a dead cat. I could not get anything useful out of the upstream O2 sensors (air fuel mixture sensors?). I'm not sure how to interpret those.

Might the Evap system issues be linked or do people think that these are different issues?
 

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Look up Scotty Kilmer on Utube he has a video on cleaning catalytic converters. I would try that first before replacing parts. Good luck.
 

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Discussion Starter #4
Another thing I noticed, but forgot to mention is that the short term fuel trim is +8 to +13 or so. It stayed up while revving.
My understanding is that this indicates that the upstream O2 sensor (air fuel mixture) is reporting a lean condition, and that the engine is compensating by trying to add more fuel than it should.
Eastern Catalytic has an interesting page where they state:
***Running too lean – High positive fuel corrections can be traced to MAF and O2 sensor faults, vacuum leaks from intake gaskets/hoses, unmetered air (intake snorkel leak), clogged or dirty fuel injectors, fuel delivery issues, and exhaust restrictions such as a clogged catalytic converter.***

The only thing that makes sense to me about laquer thinner is that it might clean a fuel injector, which could presumably result in a positive fuel trim and maybe a cat code. Otherwise, it gets combusted, so how is it going to clean build up on a cat? Doesn't make much sense to me.
 

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2007 Nimbus Grey Metallic RTL
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Swap out all the O2 sensors, run through a few tanks of premium fuel mixed with some high-quality fuel injector cleaner (Techron or Seafoam) and maybe try getting a new gas cap. I had a few sensors get tripped because I had a bad seal on my original cap.
 

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One of my trucks had the same code a couple of years ago when it first got cold outside. I reset the light and drove it like normal. It came back about a week later. I reset it again. I haven't seen it since. P0420 isn't a code that is going to make your truck engine explode or even get bad gas mileage.
 

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Discussion Starter #8
Thanks Chris. For better or worse, I live in an area that requires an emission test, which means that all emissions tests have to pass the car's internal tests. I'm also concerned that the fuel trim indicates a problem.
Interestingly, the engine light went out, and the P0420 code went away when it got really cold. The p0443 persisted, even though the check engine light went off. I put in 93 octane costco gas, and will buy a new gas cap and go from there.
 

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Thanks Chris. For better or worse, I live in an area that requires an emission test, which means that all emissions tests have to pass the car's internal tests. I'm also concerned that the fuel trim indicates a problem.
Interestingly, the engine light went out, and the P0420 code went away when it got really cold. The p0443 persisted, even though the check engine light went off. I put in 93 octane costco gas, and will buy a new gas cap and go from there.
93 octane Kirkland (Costco) gas is all I use. If I'm in a pinch, I'll pay a bit more to fill up at the BP that's close to my house, but no matter what I'm always using top tier fuel. No Sunoco, no Get-Go, no mom n pop gas stations for me. The Costco 93 octane is usually right about the same price as every other station's 87, so it just makes sense to use the Kirkland gas.

I hope your issues are simply sensor and age related. It sounds like the truck is running fine other than the thrown codes, which is a good thing.
 

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I have a friend :wink: that did the "non fouler trick" and the P0420 hasn't come back in over three years. I don't know what the legal ramifications are, but it does work and is a pretty simple (about 30 minutes) fix!
 

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Discussion Starter #12
An update:
Have run 2/3 of a tank of costco 93 octane gas through the truck. The cat code disappeared briefly, but came back. The evap code persists. On that tank, I got 15.3 mpg, which I think is bad but not terrible. Fuelly has the average at about 17. It was a 50/50 mix of around town/highway. I have realized that it has the same fuel cap as my element, so I will swap those to check that easy fix, and then I'll have the vacuum lines tested if that doesn't work.
 

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An update:
Have run 2/3 of a tank of costco 93 octane gas through the truck. The cat code disappeared briefly, but came back. The evap code persists. On that tank, I got 15.3 mpg, which I think is bad but not terrible. Fuelly has the average at about 17. It was a 50/50 mix of around town/highway. I have realized that it has the same fuel cap as my element, so I will swap those to check that easy fix, and then I'll have the vacuum lines tested if that doesn't work.
It's going to take at least 2-3 tanks of premium for the the truck to "learn" that it has premium in it. Give it a little time. As long as the truck still feels fine, you don't have much to worry about yet. If anything, you may want to look into the idle learn procedure (ILP). It's a simple thing that doesn't take much time to do and can be helpful. It may do absolutely nothing, but at least you tried. Directions for the ILP can be found here:

http://www.ridgelineownersclub.com/...ttern-learn-procedures.html?40994=#post588480
 

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Discussion Starter #14
Thanks Ian. I am supposed to get it to pass emissions by the end of December, and I don't drive that much. I'll see if I can get my wife to commute with it a bit to get the miles in. Interestingly, my region now has physical emission testers on the road in various places. I drove by one a few times today, and am curious to see if it passes as is. I'll look into the idle procedure.
 

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Discussion Starter #15
Another update:
The truck passed the roadside emissions test. They look for HC (unburned hydrocarbons), CO (carbon monoxide), and NO (nitrogen oxide). They had two observations, and both were well below the emission limits. So, despite the catalyst performance and evap codes, the catalyst seems to be working well enough. This will give me some time to see if the car autocorrects, and work on it in the spring when it warms up.

HC, ppm: 3 & 0. Limit was 74.
CO, %: 0.12 & 0.17. Limit was 0.41
NO, ppm: 34 & 41. Limit was 500
 

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^^ That's great news and a solid indication that everything mechanical/chemical is working the way it's supposed to. It's got to be a faulty sensor or something of that nature throwing off a code. Rest assured that you'll be fine for awhile, like you said. In the meantime, can't hurt to get a new fuel cap. It likely won't solve anything because you'll usually the "check fuel cap" message upon startup when the cap is actually an issue. Nevertheless, it's cheap and an easy way to rule out any vacuum leaks from the gas cap seal.
 
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