Check Engine Light - Performance Forum

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Check Engine Light
Friday, June 19, 2009 1:46 PM
ok so, I have had a catback exhaust on my car since it was brand new and it currently has 80,000 miles on it, just recently I did a header install with another custom catback. Everything has been great except for that damn yellow/orangish check light with the symbol popped up today...Getting new fogs installed this coming week by GM so I guess I can have them check it out...Ok so what I'm saying is should I be worried?

Thanks You All

-Brian T.

Re: Check Engine Light
Friday, June 19, 2009 1:47 PM
Just for reference, its a 2004 ECO
Re: Check Engine Light
Friday, June 19, 2009 2:31 PM
if you have them check it out, and the car is not under warranty, then it'll cost you at least an hour's labour. go to any local chain auto parts store (advance, autozone, etc...) and they'll read the code for free. chances are, its the rear o2 sensor acting up.



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Re: Check Engine Light
Friday, June 19, 2009 2:53 PM
Dude, thats exactly what I did( Went to Autozone) and your right, put it didn't specify which 02 sensor. It said that the 02 sensor is below threshold or something...put he erased the code and said if it pops up again then take action...I wander how I can tell which o2 it might be??
Re: Check Engine Light
Friday, June 19, 2009 2:59 PM
99% sure it'd be the rear o2 (after the cat). If it pops on again, you might try searching up the mechanical O2 simulator - should take care of the issue. However in many cases (at least my experience) once you clear the code, it won't come back. I've had header + HFC + catback on my '98 with the 2.4 for a year now and I think the rear O2 code might have come on once or something like that. But each car can be different. I also had both O2 sensors replaced when I had the exhaust done since there were over 100K miles on the car and they seemed to be the original ones. Few extra $$$ but not that much.
Re: Check Engine Light
Friday, June 19, 2009 3:15 PM
O alright then, Im wondering if I should just replace both anyways...I plan on haning onto the car for awhile...Well thanks a lot for your help man.
Re: Check Engine Light
Friday, June 19, 2009 3:18 PM
Also, whats the worst that can happen by not taking action now if the rear one is going out? Lose gas mileage?
Re: Check Engine Light
Friday, June 19, 2009 3:36 PM
your cooling fan will be on constantly. thats about it. and, you wont be able to pass inspection should you need to. if you do replace them, use delco o2 sensors only. bosch are junk.



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Re: Check Engine Light
Friday, June 19, 2009 11:10 PM
my light has been on forever. After about 10,000 miles of my high flow cat it came on... if it is saying catalyst efficeny below threshold or something or if its code p402 or something like that its your rear O2 sensor. I wouldnt worry about it. Also my cooling fan isnt on constantly. but I dont know if it would pass inspection, I dont live in a place where it needs to be eco friendly.
Re: Check Engine Light
Saturday, June 20, 2009 5:43 PM
OO alright everyone! Thanks a lot Yea my light hasn't came back on either!
Re: Check Engine Light
Saturday, June 20, 2009 9:12 PM
it will come back on eventually, it just hasnt picked up the issue yet... If it came on and then you havent changed anything on your car it will come back. Probably by tomorrow. Mine stayed off for 2 days after I cleared it. It will come back if the problem isnt fixed.

Re: Check Engine Light
Sunday, June 21, 2009 5:15 PM
The code you are talking about is P0420 - Catalytic Converter Efficiency Below Threshold. Normally that is telling you one of two problems, either your O2 sensor is starting to die on you or you Cat is no good anymore. 95% of the time a high flow cat will also kick this code as it is not cleaning the exhaust as much as it needs to.



Re: Check Engine Light
Sunday, June 21, 2009 5:41 PM
exactly
Re: Check Engine Light
Sunday, August 02, 2009 2:21 PM
Brian Toney wrote:ok so, I have had a catback exhaust on my car since it was brand new and it currently has 80,000 miles on it, just recently I did a header install with another custom catback. Everything has been great except for that damn yellow/orangish check light with the symbol popped up today...Getting new fogs installed this coming week by GM so I guess I can have them check it out...Ok so what I'm saying is should I be worried?

Thanks You All

-Brian T.


I have the exact same problem! I installed my Tsudo header yesterday and got a 2.5 exhaust done with a magnaflow high flow cat. My check engine light came on just as I arrived home from the shop that welded my exhaust, which is literally a 2min drive.

I used RTV gastket to seal one seciton of the header, and i've heard that when that stuff melts off on the inside, it can foul up the secondary O2 sensor.

The car drives fine, and sounds great, so is it safe to drive for awhile? At least until i get a new sensor? (prolly off ebay, so I'll have to wait on shipping)

Also, will a new O2 sensor fix the problem (get rid of the light) if it is the P0420 code. Or am I doomed to having that ugly light on my dash because the cat is a "high flow"?
Re: Check Engine Light
Sunday, August 02, 2009 2:35 PM
is there any type of computer reset or anything you have to do when you unplug your O2 sensor that would make it throw a code?? I had to remove my cam cover too, but that wouldn't throw a code.......i don't think....
Re: Check Engine Light
Saturday, August 08, 2009 8:52 AM
Thread too dead?
Re: Check Engine Light
Monday, August 10, 2009 12:45 PM
Mo Joe wrote:is there any type of computer reset or anything you have to do when you unplug your O2 sensor that would make it throw a code?? I had to remove my cam cover too, but that wouldn't throw a code.......i don't think....


Now unless you unplugged it and started the car.. and the valve cover wouldn't throw a code..


Ever think about sea foaming your car? clean the carbon build up off and the cat out a little bit?



Re: Check Engine Light
Monday, August 10, 2009 2:17 PM
SS-J wrote:Now unless you unplugged it and started the car.. and the valve cover wouldn't throw a code..


Ever think about sea foaming your car? clean the carbon build up off and the cat out a little bit?



I did drive to the exhaust shop with just the one sensor plugged into the header. Could it be as simple as clearing the code? The second O2 sensor was uplugged from the wire harness .
Re: Check Engine Light
Monday, August 10, 2009 2:20 PM
my cat is brand new and when i took off my valve cover is was pretty clean underneath.

You think sea foam is a good idea at 115 000 kms?
Re: Check Engine Light
Monday, August 10, 2009 3:32 PM
Mo Joe wrote:The second O2 sensor was uplugged from the wire harness .


this is your issue. plug it back in, and disconnect the battery for 30 minutes.



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Re: Check Engine Light
Tuesday, August 11, 2009 8:35 PM
Rich Grayo Jr. wrote:

this is your issue. plug it back in, and disconnect the battery for 30 minutes.


I plugged it in as soon as my exhaust was installed.

I finally got my hands on a obd2 code reader. I cleared the code and it came back on about an hour later when i was at a stop light. It's still the o2 heater circuit.

I was reading the voltages , live, off of my O2 sensors. Sensor 1 sits at a constant 0.450-0.455 v at idle, but sensor 2 was totally erratic. 0.850 - 0.060v. Does this verify that it IS in fact my second O2 sensor?

I just don't want to buy a sensor for nothing. although i do have 100 000+ kms......hmmmmmm. decisions decisions........

Re: Check Engine Light
Wednesday, August 12, 2009 3:00 PM
Its the high flow cat, mine set off the same code, have to live with the light on or maybe hptuners can make it turn off permanently, the light will come back on because you never solved the problem.
Re: Check Engine Light
Thursday, August 13, 2009 8:48 AM
Jason Brantner wrote:Its the high flow cat, mine set off the same code, have to live with the light on or maybe hptuners can make it turn off permanently, the light will come back on because you never solved the problem.



So you drive around with the light on? All the time?
Re: Check Engine Light
Thursday, August 13, 2009 5:29 PM
yep, I just stop at autozone like once a month or so and use the code reader for free to make sure no other codes pop up, It doesnt bother me anymore like it used to but there is really no way to get around it with a high flow cat on or like I am now without a cat
Re: Check Engine Light
Saturday, August 15, 2009 8:27 PM
Jason Brantner wrote:yep, I just stop at autozone like once a month or so and use the code reader for free to make sure no other codes pop up, It doesnt bother me anymore like it used to but there is really no way to get around it with a high flow cat on or like I am now without a cat


I refuse to believe that there is no way to get rid of the light. And like I said before, I am burning way too much gas for this to be a good thing. I'm still in the process of troubleshooting, but I'll let you know when I fix the problem.

There are people who have high flow cats and no light, so I know it's possible.
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