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Discussion Starter #1
My trans went out(big surprise) and about 2 weeks before the tranny gave up I get this 420 code for cat efficiency below threshold bank 1 but the engine ran great. Normally I almost never let anyone work on my stuff but pulling the trans my self was a bit more than I'm capable with what I have to work with(I figure its a tad heavier than the one in my Jetta which I've had out 3 times. Not having $3000 to spend I took a chance on a friend of a friend who fixes all the folks vehicles at their church who said they could do it for half that(cue ominous music). The trans works fine, However here's the issue, The idle was bouncing from 1500 to 2000, sometimes staying about 2000. He replaced the Idle air control valve because a code came up and told me the MAP sensor code also came up and that if I replace that it should be fine but I don't like just throwing parts at vehicle Hoping it fixes the problem, especially $80 parts. I'm gonna try following the factory manuals test of the Map sensor tomorow but like I said the van ran great before.
So my question is has anyone had a similar issue after a trans issue that might be the problem or just any ideas? Would an O2 cause this kind of fluctaution? After driving it store codes 0420 and 0505. The EGR passage was clear when I checked right before the trans quit. I consider myself a decent mechanic so I should be able to answer any questions that might help find the problem. Thank You
 

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A P0420 is as you said - low cat efficiency. Basically, it indicates that the cat cannot burn off all of the remaining fuel in the engine exhaust. But the rear sensor is just a monitor, and nothing more. Unlike the front sensor that actually feeds back to the ECM to adjust fuel mixture, the rear sensor is simply a tattle-tale. For purposes of diagnosing the idle issue, ignore it.

I believe that P0505 is your culprit - that has more to do with idle speed control??? That could be the IAC, or just as likely a vacuum leak somewhere. In the tranny service, were any vacuum lines disconnected? Look for a cracked hose or damaged barb. You also mentioned doing the EGR - another place with vacuum lines and intake manifold gaskets that might not be properly sealed.

'Back in the day' transmissions had vacuum modulators as well as mechanical and some electronics to govern shifting. Another place to check for a vacuum leak.

I'm not big on doing this myself, but do you know how to use an unlit propane torch for looking for a vacuum leak?
 

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About an hour after I read your suggestion I was talking with a coworker and he suggested the same thing.When I got home I was all out propane so I used some starter fluid and what do you know, there was a vacuum line off on the Intake Air Diverter Valve(I think thats right I'm not home to check). This unit has a vacuum line running from each side if the intake and required the removal of the upper part of the manifold so I could reattach it.I'm not even sure how the guy got it off in the first place but no matter, the van runs great and hasn't faulted any codes over the last couple hours of driving. Thanks a bunch for the help, not knowing where to look is the worst and it helps when someone else confirms that I'm looking where they would.
 

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Hey, I just love a happy ending! Glad I was able to help.
 
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