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Discussion Starter · #1 · (Edited)
OK so recently I bought a 1997 Honda prelude SH and shortly after purchasing it is the ECU went bad. Thankfully I was able to get an ECU with the whole immobilizer set up and key off of eBay for like $260. Got my car back from the shop yesterday and it starts just fine and is running just fine. No noticeable issues at all. Just as flawless as when I bought it.

However.....

The shop pointed out to me that ever since installing the new ECU and immobilizer, the check engine light is now on and it is throwing the codes P0453 and P0450. These codes are both EVAP/emissions codes related to the fuel tank pressure sensor.

Now my question is, is this something to do with the ECU that was put in my car? The fact that it is out of a 2000 model SH and mine is a 1997 SH? Or did my car all of a sudden developed an EVAP leak/FTP sensor failure while it was sitting idly not running for three weeks while the shop was trying to get to fixing it? I just find that a little hard to believe considering before the ECU failed the check engine light never came on in my car. Granted I had not had it for very long, but my mechanic friend had checked it out before the ECU failed and he said the ECU did not show a check engine light being on in the last 90 days.

Is there some ECU incompatibility or difference in emissions standards parameters from the 1997 SH to the 2000 SH that would cause the new ECU to throw these codes or is there really an FTP sensor issue with my car? Either way I'm going to get it looked at soon as I recuperate financially from this most recent repair. But I am just curious as to if any of you could offer some insight. Thank you!!
 

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As far as I know the 1997 (49state model) doesn't have the same emissions setup as the later models.

The 97 used a evap canister that was stand alone without any purge valve or switch physically mounted onto it, rather they are connected via vacuum hose and the canister is much smaller than on the later model years which also integrate the solenoid/switch into the top of the canister.

The later models (and the California version of the 97) also had some extra things mounted on the firewall sort of above the canister, mainly a fuel tank pressure sensor and a couple other things that where different then on the 97 models. Whereas the 97 49st model only has the evap purge flow switch above the canister.

Basically what I think is happening is that your new 2000 model ECU is looking for things (sensors and such) that aren't there (your 97 model doesn't have them). This is just a guess however.

Consult chapter 11 of your FSM if you want to learn more (it has great pictures that show the differences between the various years). I have spent the last couple months trying to chase down an evap problem on my 97 (49st version) learning way more about the 5th gen lude evap system than I ever wanted to know. Let me know if you have any more questions.
 

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Discussion Starter · #3 ·
As far as I know the 1997 (49state model) doesn't have the same emissions setup as the later models.

The 97 used a evap canister that was stand alone without any purge valve or switch physically mounted onto it, rather they are connected via vacuum hose and the canister is much smaller than on the later model years which also integrate the solenoid/switch into the top of the canister.

The later models (and the California version of the 97) also had some extra things mounted on the firewall sort of above the canister, mainly a fuel tank pressure sensor and a couple other things that where different then on the 97 models. Whereas the 97 49st model only has the evap purge flow switch above the canister.

Basically what I think is happening is that your new 2000 model ECU is looking for things (sensors and such) that aren't there (your 97 model doesn't have them). This is just a guess however.

Consult chapter 11 of your FSM if you want to learn more (it has great pictures that show the differences between the various years). I have spent the last couple months trying to chase down an evap problem on my 97 (49st version) learning way more about the 5th gen lude evap system than I ever wanted to know. Let me know if you have any more questions.
Thank you so much for the helpful insight!! That makes sense and explains a lot. I now remember reading a while back that the ECU from the 99 and forward would work in a 97, however there are small difference in the emissions and whatnot that could give a false check engine light, which I am guessing is going on with mine.

With that said, I wonder how hard it would be to get mine to stop throwing those codes. Would it be difficult or even possible to change my EVAP canister to 99-01 cannister and add the FTP that my ECU is looking for? I know it's not causing any mechanical issues, but I was wondering for the sake of being able to get my car inspected as my inspection sticker expired the end of this month.
 

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Thank you so much for the helpful insight!! That makes sense and explains a lot. I now remember reading a while back that the ECU from the 99 and forward would work in a 97, however there are small difference in the emissions and whatnot that could give a false check engine light, which I am guessing is going on with mine.

With that said, I wonder how hard it would be to get mine to stop throwing those codes. Would it be difficult or even possible to change my EVAP canister to 99-01 cannister and add the FTP that my ECU is looking for? I know it's not causing any mechanical issues, but I was wondering for the sake of being able to get my car inspected as my inspection sticker expired the end of this month.
I'd have to look at my friends 98 but I think there is probably extra wiring for the extra sensors. I suppose there might be some way to wire it all in there, unless the car already has it just tucked away somewhere. I feel like the easiest way would be to find a 97 49st ecu, not the most cost efficient probably in your case though :(
 

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Discussion Starter · #5 · (Edited)
I'd have to look at my friends 98 but I think there is probably extra wiring for the extra sensors. I suppose there might be some way to wire it all in there, unless the car already has it just tucked away somewhere. I feel like the easiest way would be to find a 97 49st ecu, not the most cost efficient probably in your case though :(
Yeah that's kind of what I'm thinking as well. But being that I went through such an ordeal getting the one that I bought put in because of how backed up the shop was, and even though I saved a lot of money it still cost me a pretty penny with the labor and all, I think I'm just going to roll with the one I have for now

I don't foresee this causing any mechanical issues, since the computer is just looking for something that never existed in my car to begin with. In the meantime if I do happen to come across an ECU and key/immobilizer set up for a 97 SH for a decent price I will go ahead and pick it up and swap it out when I get a chance.

However if you do happen to find in your friends 98 that there are wires already in there for the extra sensors then definitely let me know! That would be kind of awesome. Haha

Thank you for your help.
 
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