My si has 102k miles on it and I finally got my first check engine light:

P0420 Catalyst system efficiency below threshold (Bank #1)

I'm wondering if it's the cat or one of the o2 sensors. Which one usually goes out first?

Help needed...

 

usually the o2 sensor's go first, but they usually throw a low voltage oxygen sensor code.

by the description of that code it seems like you'll need a new cat.

 

I'm not near my car information, but I know the emission parts have a different warranty than the rest of the car. You might be covered. I'll post later if someone doesn't confirm this first.

 

yeah, I was reading the chilton manual and it cleared things up for me.

since it's an OBDII car, there are two o2 sensors:

1. PHO2 - primary heated O2 sensor
-----used to determine rich/lean conditions based on amount of O2
-----100-300mV = lean
-----700-900mV = rich
-----the output of the primary should look like an oscillator
-----the ecu uses this data to set the fuel injector duty cycle


2. SHO2 - secondary heated O2 sensor
-----this one is not used for the air/fuel calculation
-----used to monitor the efficiency of the PHO2 and the cat.
-----the output of this one should not fluctuate like the PHO2 sensor
-----if it does, the cat is bad.

they don't start working until they reach a temp of 1100F. the reason why they're 4 wire is because 2 of the wires are simply to drive a heating element so that the sensor starts working sooner. H = Heated. the other wires are simply for the O2 signal and ground.

those cats are like $500 from honda!! yikes. now I hope it's one of the sensors and not the cat.

 

I'm thinking it's just one of your O2 sensors. Could be the cat. If so don't get another one from honda if it is 500 bucks. Lemme check I think I have my stock 1999 si cat I will let go for cheap.

 

I called honda and they quoted me on a new cat: $1200

I also asked about the warranty and they said it's not covered. Buzzbomb, let me know when you get a chance...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by chris_B16A2 &raquo;</TD></TR><TR><TD CLASS="quote">those cats are like $500 from honda!! yikes. now I hope it's one of the sensors and not the cat.


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those o2 sensor's aren't cheap either. IIRC they're $320 or near there.

Mine originally blew at 55k miles (typical according to some research)

I threw another CEL on my cross-country trip, but it went away after driving on the east coast for 1 week. I think it was the octane (east of the shanendoah valley Premium is 93 octane, west is mostly 91 octane) -- i think that was why it blew, but it just simply went away. I threw a p031 or whatever is the primary o2 sensor low-voltage CEL code.

 

R_star, ok thanks

 

Sijray21, yep, seems like all that emissions stuff is too expensive.

 

Here's what I have availible. A gs-r cat from a 94-97 acura integra gs-r. Unknown milage but was working when pulled out from car. Come's with O2 sensor. They are the same size I believe. You will have to do some minor fab with this only to extend the O2 sensor's wires.





-Sorry I already sold the si one. The gs-r one is the only other one I have.


<FONT COLOR="green"> * Also forsale is stock 1999 Honda Civic Si header. </FONT> make offer

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by chris_B16A2 &raquo;</TD></TR><TR><TD CLASS="quote">I called honda and they quoted me on a new cat: $1200

I also asked about the warranty and they said it's not covered. Buzzbomb, let me know when you get a chance...</TD></TR></TABLE>

I just checked my warranty information and the cat is covered by an 8 year / 80,000 mile warranty. Whichever comes first. Since your car has over 100K miles, it's not covered.

You should be able to find a used one for pretty cheap.

 

Wow, thats alot of miles!! And still going strong!! yeah baby!

 

https://honda-tech.com/zerothread?id=1284376

These guys might still have a CAT. PM then and find out.

 

why dont you consider just egtting a carsound high flow cat and installing an o2 bung?

 

d00d just buy the one I have.

 

I ended up taking it into the local honda/acura specialist today to get the timing belt, water pump, seals, drive belts, valves adjusted.... and I mentioned the code to them.

The mechanic said that it could be that my cheap plugs were worn out. He took one out and sure enough... So I ended up with some new Desno Platinums.

If they light turns back on I may have to buy the cat. Hopefully is stays off...