ECU Reflash/P0420 (1 Viewer)

Joined
Aug 7, 2006
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944
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Northern Virginia
I have the intermittent P0420. It probably comes every 100 miles and I just clear it with my scan gauge. But I'd rather not have it.

I have new OEM O2 sensors and new cats. Those made no difference.

Anyway, today I was reading on another forum (sorry, sometimes I stray) a posting about an 01 Lexus with a recurring P0420. A tech chimed in that some toyotas of that vintage need an ECU reflash to cure it.

Any thoughts? If a reflash is relatively cheap, I'd be willing to try it.

Edit: Here's another example of a reflash curing the P0420:Toyota ECU Flash / Recalibration with the MasterTech
 
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Joined
Jul 19, 2010
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231
Location
NoVA
 
 
My CEL just came on 2 days ago and I scanned it to be P0420 as well. I'd be interested in this "reflash" procedure as well although I still don't know what it means after reading your hyperlink to Art's automotive.

BTW, where are you in Northern VA? I'm in Ashburn and my is a 95 LC as well.
 
Joined
Dec 13, 2007
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Germantown, TN
 
This may not apply here but it is worth a try. Have you tried disconnecting both terminals of the battery for a couple minutes...then reconnect. That cleared mine 6 months ago and it has not returned. If you have an alarm system have your key-fob ready on battery reconnect as it is likely to sound.
 
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Northern Virginia
From further reading, it sounds like it may have something to do with ethanol and different gas formulations that weren't considered when they did the original mapping. Even some cars from the early 2000s have this issue. One site showed a guy getting his ECU reflashed for $94. As long as they don't fry the thing, I'm not sure how it could hurt.

Skippingrocks - clearing the code isn't an issue. Or are you saying a prolonged disconnect resets the ECU?

Ftbagkicker - I'm in PW County south of Manassas.
 

landtank

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that code is typically a cat issue. Have you checked the joint between the two cats for a leak?
 
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No leaks that I can tell. The cats are aftermarket and welded in. The welds look good and I can't see or feel any leaks.

The Y pipe had a small leak a while back, but I had that fixed when I did the new exhaust. As best as I can tell, that leak is sealed.
 
Joined
Dec 13, 2007
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Germantown, TN
 
All I know is that after changing my battery which had a long disconnect time...the initial computer startup rev sequence reset everything that a mechanic could not. I haven't had a cat code since. It's a simple cost free try for fixing the symptom but not the problem.
 
Joined
Dec 10, 2007
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Not the ECU expert, but AFAIK disconnecting the battery removes the ECU's volatile memory (codes and recent sensor data), like when the power goes out at your home, you lose what you're working on (assuming no auto-save features), it's gone, but all the firmware (programs) on your hard drive are still there. The idle is funky because the ECU is collecting data again from all the sensors to use along with the programmed instructions that remained in the ECU.
 
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