I just purchased a used 03 HCH and have put about 500 miles on the car. The check engine light came on this past Saturday. It didn't seem to have any effect on performance or gas mileage. As I drove the car my mpg continued to rise. By the time I completed my road trip of about 400 miles, my mpg was showing 51.4. When I got home I hooked up the scanner. The code came up as a manufacture specific P1420. I reset the code, but it came back the next day. I have not been able to find out what that code means. Any information on this would be greatly appreciated. Thank you!!!

 

Check this post it may help. I had the same code.

https://www.greenhybrid.com/discuss/...20-code-19634/

 

I checked with my local Honda dealer. The service manager looked up the code in his computer. He said that it could have something to do with the cat, but said it was the 3-way cat, which is the one coming off the manifold. He said that there is a software update for the ECM and suggested that we do that first. The update is supposed to change the threshold and might prevent the ECM from setting a code. As long as there is nothing wrong with the cat, the software update should fix the problem. I did reset the mil and it hasn't come back on for a couple of days. If it does I will make an appointment to have the software update done and see how it goes. I will keep posting, until we resolve this issue. Thanks for your reply!!

 

That is seems to be the same problem i have i was thinking of having the ECM re programed too but i have not had the time and that might be the problem. it seems to me that when i step on the gas all the way to pass some one or to floor it to get on the highway it comes on and pops that code up about 30 secods later.

 

As it stands right now, my check engine light has not come back on since I reset it the 2nd time. When and if it does come on, I will take it to my local Honda dealer to have software updated.

 

i searched for an answer about this one and i got this. the reason may be result of hitting the so hard. the solution might be to reset the code and monitor it.

another maybe the problem is the intake constructor CTRL circuit open.
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This is an old thread, but I thought some info here. The 03 Hybrids had a factory software/programming defect. The defect causes the engine to run lean and, over time, this burns up the catalytic converters. Honda has issued a software patch for this, but once the O2 sensors or cats are burned up, they have to be replaced. There was a class action lawsuit filed against Honda, because they would not warranty the replacement of the burned up cats and O2 sensors. The result of the lawsuit was that all owners would get a gift certificate, per se, to be used against the purchase of a new Honda. Big woop. Honda also had a problem with the Hybrid CVT transmissions. They would slip and balk badly (defective start clutches). Honda reformulated the CVT fluid to try and help solve this, but if too much wear had already occurred, then the tranny would quickly exhibit the same symptoms. Again class action lawsuit and again no fix from Honda. See the pattern? I could go on with the battery packs, etc, but you get the drift.....