OK. I have an 07 Accord 4cyl 5spd MT with 92k mi that is spitting out a P0420, catalyst below threshold, code. I see there's a TSB for 06-07 that says it could be a software problem. My question is how do I know if this applies. The TSB only applies to KL vehicles. Mine is a LEV that states under the hood" This vehicle conforms to US EPA tier 2 bin 5 regulations applicable to 2007 model year new passenger cars and California regulations applicable to 2007 model year new LEV II LEV passenger cars." So do I have a KA or KL vehicle?

At this point I don't have any other codes, but the P0420 is consistent. I've tried simply resetting it, only to have it return. I know I don't have a large exhaust leak. My plan is to get under it tomorrow and look for a small leak. It has never had a coolant loss issue so I doubt coolant is fouling the cat. It does use oil, but not a ton. Perhaps it uses a quart every 2 to 3 kmi. Basically I have to add a quart once between oil changes. I hooked up a scan tool. The first O2 sensor is right where it should be, with lambda bouncing between .97 and 1.03. The second sensor bounces up and down, but will settle in eventually during a steady cruise. It did have a few misfires while I had the tool hooked up, but not anywhere near enough to be a problem. I do still have the original plug in it, but they aren't due to be changed for another 15k.

My thought was, if I don't find an exhaust leak, and if it is a KA vehicle, to change the cat and put in new plugs. But if it could be just a software issue, that would be real useful info. Thanks all.

 

Go to honda
Tell them to perform pcm update
There is a pcm update for every honda at this time
But if 0420 comes back right after you clear the code then i think its a bad cat
If it comes back after about a 1k miles i think its a software issue
Just so you know the update is not just to fix 0420 codes
They throw in other updates at the same time
You cant just pick the one update

 

Well I couldn't find an exhaust leak. I did find a small oil leak, so it may not be burning oil after all. I measured temperature of the cat and found the output about the same as the input. I think this is a good measure of cat function and it shows mine isn't doing much if anything. I may get the software update done anyway, but it's looking like it's time to replace the cat.

 

So I took it to the dealer to get the software updated. They wouldn't do it. Looked it up, found it's a KA, said the TSB didn't apply, and said they wouldn't load newer software. They said it wouldn't help the P0420 problem and could cause other problems. At least they didn't charge me for this advice. They wanted to diagnose the problem themselves, and charge me for that. I didn't go for it though. They did say that, based on what I told them, it would likely need a new cat. Oh Joy.

 

I don't understand
Once they hook up something called MVCI
And it will tell them if the PCM would accept the new software

 

Mvci is the talk between when our hds talks to the ecu.

 

Hds software is outdated and there is no new software plus its slow compared to mvci

 

Incorrect. The software IS HDS.The MVCI is simply the new HARDWARE. It is the new interface,but the software is still the Honda Diagnostic System......

 

KA is a California vehicle and the update doesnt apply......

 

He wouldn't even hook it up. They said the update didn't apply and they wouldn't update software if there wasn't a problem. They were saying the P0420 code was likely a cat problem, and wasn't a software problem.

 

If I want to insist on getting the software updated, I'll have to go elsewhere. At this point, I don't know that this is worth the time.

 

9 1/2 times out of ten it needs a cat. They won't update anything that's not specified under a bulletin unless maybe you would pay for it because Honda will not pay for it and they don't want an adverse effect if the update would also change something that should not be

 

I was planning on paying for it. I think it's listed as .6 hours including a test drive afterwards. Money wasn't the question. They just wouldn't do the job unless the TSB said is was needed.

 

The update doesn't apply to your vehicle,the update may or may not cause driviabilty issues to your vehicle,why would you insist on having it done????

 

I'm not insisting on it. But in any case, the plot thickens. I went out with the scan tool again. I wanted to look at the live data again and see if I came to the same conclusion. This time there was another code, a temporary one, present. It is P0139. The P0420 is still set as a permanent code even though the CEL is now out. P0139 is a slow responding rear O2 sensor. Hmmm. Now the P420 code sets if the rear O2 sensor bounces up and down too much. I would think a slow responding rear O2 would make it less likely to pick up a P0420. On the other hand the two are surely related. Could a bad cat have caused the rear O2 to fail? Even though it doesn't make sense to me, I'm thinking I should just replace the rear O2 because it's much cheaper than a converter. I think Denso is OEM, so I'll probably go that route with the sensor.

 

Yes,replace the rear O2 first. Then retest....