P0420 code on 2008 Prix


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guitarfish
12-05-2011, 09:01 PM
My '08 just hit 150K miles, and a little present appeared in the instrument panel, an orange colored engine light. (They should make it a green colored $ sign, because that's what it really means :rofl:).

Got it scanned tonight and it's a P0420. Did lots of searching on this board, it seems like it's the catalytic converter, or possibly the rear O2 sensor.

Not sure what I can do to troubleshoot. I'd love to hear experiences/suggestions.

Thanks!

NOTE - THIS ISSUE IS FIXED. See here (http://www.automotiveforums.com/vbulletin/showpost.php?p=6967182&postcount=69) for the result.

Tech II
12-05-2011, 10:14 PM
What would help is if you have a scan tool that can plot the pre and post O2 sensors......when the cat is functioning normally, the pre O2 sensor is like a sine wave fluctuating from 0.2-0.8 volts, constantly changing.....

The rear O2 sensor should move slowly, staying high, then switching and staying low(depending on whether the cat is storing or using O2).....but it should switch nowhere near as fast as the pre sensor...


When the cat is bad, the waveform of the rear will mirror image the front one, and change just as rapidly.....

olopezm
12-06-2011, 10:09 PM
Most of the time you can identify a bad cat converter because of a sulfur or rotten egg smell coming out from the tail pipe. Are you noticing any?

If the cat has clogged then you should be able to see it glowing red after a few moments of starting the engine; a clogged cat should also cause a lack of power...

Oscar.

guitarfish
12-06-2011, 10:46 PM
I had a baf cat once before on a different Prix, with definite noticable symptoms. It was an '02 with one of the bad factory cats, which GM replaced. This time, the only symptom I have at the moment is the SES light. Thanks for the tips though, I need to do more investigating.

GTP Dad
12-07-2011, 10:31 AM
If you have no driveability issues I would change the rear O2 sensor and see if the problem goes away. The rear sensor can go bad and will set a similar code about the cat being bad. If the problem persists I would have the cat checked.

Tech II
12-07-2011, 01:07 PM
Kind of leaning towards GTP Dad on this one.....more often than not, if you have to replace the cat, you should replace the rear O2 also......so it couldn't hurt to do so......

rkvons
12-07-2011, 01:40 PM
I was under the impression that when you start your car, two tests will be performed on the cat system. The first one happens right away and verifies that the pre and post cat sensors are reading about the same. The second test happens after the vehicle goes into closed-loop. This time the system checks to see if the readings are different between the two sensors. If they are not different enough, it fires the P0420 code. This then, points to the converter as being bad. Am I close?

guitarfish
12-25-2011, 10:47 AM
I reset the SES light by pulling the battery. It stayed off for a few days (200 mi) then came back on. Yesterday I installed a new after CAT O2 sensor yesterday and reset the SES again, will see what happens.

I noticed the CAT is bolt on. Is this a job one can do at home? Also, should I stick with a GM CAT, or is there a quality aftermarket unit that's just as good?

Thanks

GTP Dad
12-25-2011, 01:55 PM
A GM Cat is very expensive. I recommend an aftermarket cat. Try looking at Rock-auto.com for a replacement.

guitarfish
12-27-2011, 07:11 PM
Oh well, 100 mi later the SES light is back. I guess it's time to have the CAT checked. PITA.

olopezm
12-28-2011, 12:48 PM
Try erasing the codes with a capable scanner instead of disconnecting the battery (something I learned recently), maybe autozone will clear them for you.

I read somewhere they weren't doing any longer...

Oscar.

guitarfish
12-28-2011, 01:38 PM
Try erasing the codes with a capable scanner instead of disconnecting the battery (something I learned recently), maybe autozone will clear them for you.

I read somewhere they weren't doing any longer...

Oscar.

Advance Auto wouldn't clear the code for me. Not sure what the big deal is. I reset it by pulling the battery cable for a couple hours.

Tech II
12-28-2011, 02:22 PM
Disconnecting a battery does not clear a code.....There are code readers out there for 20-40 bucks when on sale....also you can buy a scan tool that will plot the pre and post O2 sensors for around 150(also reads data, codes, and clears codes).....Amazon.com has some good deals...

guitarfish
12-28-2011, 02:23 PM
Disconnecting a battery does not clear a code.....There are code readers out there for 20-40 bucks when on sale....also you can buy a scan tool that will plot the pre and post O2 sensors for around 150(also reads data, codes, and clears codes).....Amazon.com has some good deals...

Well, on my car disconnecting the battery for a couple hours resets the SES light, which is what I needed.

olopezm
12-28-2011, 08:09 PM
Well, on my car disconnecting the battery for a couple hours resets the SES light, which is what I needed.

I used to believe the same, it works in my Ford cars but not on the GP and this is how I found it out. I had been getting a p0441 DTC since a long time, I replaced all rubber parts in the EVAP system and even the gas cap. Disconnected the battery a couple of times because I did other repairs and tested the car after each, and every time the CEL came on with the same code I was tired of looking for problems and since I don't have a smoke machine (nor I know a shop who has one) I decided to leave it alone until a couple of weeks ago when the same discussion about resetting the light came up, the guys wrote that disconnecting the battery would reset the CEL but wouldn't erase the codes stored in the PCM. That was when I hooked up my scanner, deleted the code and drove the car and voila! No more DTC's; unfortunately I still have a problem with the steering XD (and a bad cat converter).

Anyway, I hope my quick story helps understand the CEL thing ;) .

Oscar.

GTP Dad
12-29-2011, 11:01 AM
I have to agree that not using a code scanner to delete the code will not clear it totally. You should find someone with a scanner and properly delete it from the computer. If it comes back on after that then a true issue exists and further diagnosis will be required.

guitarfish
12-29-2011, 11:07 AM
It sounds like what you guys are saying is that if the battery is disconnected to turn off the SES light, the light may come back on from a code previously stored in the computer, even if the problem that triggered the code is gone? That just doesn't make sense to me (which wouldn't be a first by any means when dealing with cars!) This hasn't been my experience in the past, anyway.

After clearing the SES light caused by the P0420, I drive about 5-7 trips and 150-200 miles before the light came back on. And then did this again after replacing the O2 sensor. My conclusion is that the light came back on because of a new fault event. In my case, I'm assuming the efficiency of my CAT is dropped below spec on occasion, as it is going bad.

olopezm
12-29-2011, 06:22 PM
It sounds like what you guys are saying is that if the battery is disconnected to turn off the SES light, the light may come back on from a code previously stored in the computer, even if the problem that triggered the code is gone?


That's correct; after reading the service manual I found out that DTC's are stored in an EEPROM (Electrically Erasable Programmable Read-Only Memory) and even when you disconnect the battery, the codes don't go away until the PCM performs the required routine to erase the codes (use of a capable scanner in this case). That's the difference between this memory and KAM (keep alive memory) on Fords for example.

Are you getting any rattling noise, sulfur smell or perhaps your car is overheating?. One or more of could indicate a failed/clogged cat converter.

Oscar.

guitarfish
12-29-2011, 06:35 PM
That's correct; after reading the service manual I found out that DTC's are stored in an EEPROM (Electrically Erasable Programmable Read-Only Memory) and even when you disconnect the battery, the codes don't go away until the PCM performs the required routine to erase the codes (use of a capable scanner in this case). That's the difference between this memory and KAM (keep alive memory) on Fords for example.

Are you getting any rattling noise, sulfur smell or perhaps your car is overheating?. One or more of could indicate a failed/clogged cat converter.

Oscar.

I have no symptoms other than the code. I'm the original owner, the car is well cared for, tuned up, never any issues that would normally contribute to a CAT going bad.

olopezm
12-29-2011, 07:13 PM
I'm the original owner

I wish I could say that with one of my cars! LOL.

In that case I don't think you would have anything to worry about.

Just find a shop that will erase the code for you or, if you want, you can have the exhaust pressure checked and sniffed at the dealer to make sure everything is OK. Other than that and a bad sensor I have no ideas...

Using the attached PDF you can backprobe the sensor and measure voltage with a DMM across both high and low signals. It should slowly alternate between 0.2-0.8V.

Oscar.

guitarfish
12-29-2011, 07:18 PM
I wish I could say that with one of my cars! LOL.

In that case I don't think you would have anything to worry about.

Just find a shop that will erase the code for you or, if you want, you can have the exhaust pressure checked and sniffed at the dealer to make sure everything is OK. Other than that and a bad sensor I have no ideas...

Using the attached PDF you can backprobe the sensor and measure voltage with a DMM across both high and low signals. It should slowly alternate between 0.2-0.8V.

Oscar.

I called a local Midas, about the only muffler place around. I told him I had a P0420 and I changed the O2, and they immediately quoted me a price for a CAT. I asked if they needed to do any tests first, and they were like, "nahh."

Sigh.

I'm still up in the air with this.

GTP Dad
12-29-2011, 08:42 PM
Guitarfish,

There have been a lot of suggestions sent your way on how to resolve this issue. As has been suggested have the code cleared, using a scanner, and see what happens. The P0420 code points to the cat but unless you have the code cleared it won't change anything and you may never know if the sensor fixed the issue or not. If the light comes back on after being cleared properly you will need to replace the cat. Otherwise you are going to either need to live with the light or sooner or later the car will have driveability issues and you will need to replace the cat to cure the problem.

rickisrad
12-29-2011, 08:45 PM
I called a local Midas, about the only muffler place around. I told him I had a P0420 and I changed the O2, and they immediately quoted me a price for a CAT. I asked if they needed to do any tests first, and they were like, "nahh."

Sigh.

I'm still up in the air with this.


replace the cat with a high flow one from zzp. it is around $230 for the post 06 and you will gain much more power in the mean time. http://shop.zzperformance.com/store/p/249-ZZP-Downpipes.aspx there are a few drop down options you have to choose. 4 bolts and done. I worked at Midas for 7 years and I gaurantee they will rip you off. They have to have at a minimum of 50% markup on an exhaust part alone. What was their quote? I would say with labor they probably quoted you around $4-600 depending on the manager.

rickisrad
12-29-2011, 08:49 PM
also the light will go off itself if the issue was fixed. when the computer senses the issue is resolved after the drive cycles it will turn off the ses light but may still store the code until deleted with a scanner.

guitarfish
12-29-2011, 08:55 PM
Midas quoted me $611. I hate that place. I'm not even considering it, I just wanted to see if they'd actually test it. I see mine's a bolt on, is this something I should be able to do in my garage without too much insanity?

rickisrad
12-29-2011, 09:01 PM
Midas quoted me $611. I hate that place. I'm not even considering it, I just wanted to see if they'd actually test it. I see mine's a bolt on, is this something I should be able to do in my garage without too much insanity?

I figured, we made 14% commision on the entire job so the more money the better in our situation. Unfortunately I had to sell my jobs and I hated it. you will be able to replace it in less than an hour. It is really simple four bolts, the top two you will need an extension to get to it easily. the back ones may be a little rusty but should come off with out cutting. buy the gaskets from zzp also. You will be happy with the little extra added performance and saved money.

Tech II
12-30-2011, 07:57 AM
Yeah, the manifold bolts sould come out fairly easy......the bolts after the cat could be a problem......if you have a torch, you may have to get the flange(the side with the threads) "cherry" before trying to remove them, or you will snap the heads off the bolts......

rickisrad
12-30-2011, 08:14 PM
with his being an 08 the bolts should be able to come off a little easier. they should come off with a wrench and ratchet. in our climate though, you never know.

Tech II
12-31-2011, 10:21 AM
If you live in a salt area like I do, it doesn't take long......have see bolts that look pristine that break.....it was just a heads up......

guitarfish
12-31-2011, 10:33 AM
OK, welling, planning ahead...if the bolts break, what's next? Drilling them out or what?

rickisrad
12-31-2011, 09:10 PM
yeah I live 2 miles outside of Cleveland ohio so no stranger to salt and rust. if the bolts break no big deal a 3-4 lb hammer and a chisel with a point will knock them out. A small propane torch would help. Regardless, I think you will be just fine replacing it yourself.

guitarfish
01-07-2012, 06:58 PM
Well I installed my new CAT today. Pretty straightforward. Hardest part was breaking the nuts loose. I sprayed the ones back by the resonator and let them sit overnight. I still needed a breaker bar but got em free.

The SES light is out, if I make it 300 miles and it's still out, I'll call it a success. Thanks all for the help with this!

rickisrad
01-08-2012, 04:13 PM
keep us posted!!! What cat and downpipe did you use?

guitarfish
01-08-2012, 07:23 PM
I ended up going with a MagnaFlow Direct Fit Catalytic Converter (http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product__10083748-P_145_R%7CGRPEXHAAMS____). I had a $50 coupon from Advance Auto Parts, so I got it for $189. I was happy with what I read about it on Walker's website, and it fit perfectly.

guitarfish
01-09-2012, 08:43 PM
Well I'm striking out on this one guys!! Argh!! The SES light is back. Got it scanned again today, it's still P0420 Bank 1. I've replaced the CAT and also the after CAT O2 sensor so far.

Looking through the GM service manual, I found this:
"Important: A new converter with less than 100 miles on it may set DTC P0420 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition."
My SES light came on at about 175 miles, after about 7 drive cycles, so I don't know if that applies.

I also found this:
Heated Oxygen Sensor Resistance Learn Reset Notice
Notice: When replacing the HO2S perform the following:

• A code clear with a scan tool, regardless of whether or not a DTC is set

• HO2S heater resistance learn reset with a scan tool, where available

Perform the above in order to reset the HO2S resistance learned value and avoid possible HO2S failure.

I'm not really sure what to do next.

GTP Dad
01-10-2012, 10:09 AM
This is a tough one. Replacing the cat and the sensor should have eliminated the issue unless you have other issues up stream like a rich condition from one or more cylinders that is dumping raw fuel into the system. You could have a bad injector causing this a good way to check this would be to pull the plugs and check for a wet plug. Otherwise I am at a loss on what to do next.

guitarfish
01-10-2012, 10:10 AM
What about replacing the upstream/before cat O2 sensor?

roman1978
01-10-2012, 10:36 AM
I have read before that some aftermaket converters may cause the light to stay on. The issue could be in the converter.

guitarfish
01-10-2012, 10:39 AM
I have read before that some aftermaket converters may cause the light to stay on. The issue could be in the converter.

I'd read that also, which is why I went with Walker. They are a long time established manufacturer. On their website they discuss the SES light and why one should replace their converter when necessary to clear it. I may call them today and see if they have any ideas.

roman1978
01-10-2012, 10:40 AM
Good luck

rkvons
01-10-2012, 01:35 PM
Since your Cat is bolt-on, you could take it off and have a look at it. If it is carboned up, you could fill a bin, or bucket with hot soapy water and soak it in there. Sometimes the inner surface of the Cat material gets a coating and stops working. It's worth a try.

GTP Dad
01-10-2012, 03:20 PM
Replacing the upstream sensor would decrease the possibility of too much fuel and a rich condition. You may have to purchase an O2 emulator from ZZP to eliminate the light entirely if you are unsuccessful in finding the issue causing the light to come on.

guitarfish
01-10-2012, 03:26 PM
Replacing the upstream sensor would decrease the possibility of too much fuel and a rich condition. You may have to purchase an O2 emulator from ZZP to eliminate the light entirely if you are unsuccessful in finding the issue causing the light to come on.

Man, this is crazy. I'm going to replace the upstream sensor tonight.

Thanks for the input.

guitarfish
01-10-2012, 08:33 PM
This is turning into a freaking Greek tragedy.

First, I don't have a Walker cat like I thought. Brain fart. The one I installed is a Magnaflow p/n 24205 (http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_Direct-Fit-Catalytic-Converter,-Stainless-Steel-MagnaFlow_10083748-P_145_R%7CGRPEXHAAMS_____) from Advance Auto Parts.

I bought an upstream O2 tonight, and the wiring connector wouldn't fit. Guess why? My car has a CALI-FREAKING-FORNIA emissions package installed. Nevermind that I bought it new in Pennsylvania where I live. I read the entire window sticker looking for anything about Cali emissions before buying parts, because that's where I expected it would be. FAIL. I just found a little sticker under the hood, the car complies with California PZEV blah blah blah.

So, I've installed a 49-state Cat and downstream sensor on the car.

Now, I call my guy at Advance Auto Parts, where I bought the Cat. He says the Cat and the downstream sensor I already put in are OK, it's only the upstream sensor that matters. Replace that, he says, and the light should go out. Does this make any sense??

I still have my old cat and old downstream sensor, just in case.

My brain is roasted right now, I don't know what to do next. So far I've spent $300 and wasted hours and accomplished nothing.

guitarfish
01-11-2012, 08:04 PM
Update: I called Magnaflow. They said the federal cat I installed isn't certified for the state of CA, BUT, it will handle the load from a PZEV vehicle and I shouldn't get any codes. I spoke to a friend of mine tonight who is a superb mechanic (too bad he lives halfway across the country), and he pretty much said the same thing. He also said he would've changed the upstream O2 sensor before doing the cat. Well, you know what they say about hindsight, right?

I installed the upstream O2 tonight, and will see what happens. I'm holding my breath and hoping this is finally fixed.

GTP Dad
01-12-2012, 11:18 AM
Just a note on the California issue. Several years ago PA adopted the CA emission rules for all new cars sold in the state. If you have a vehicle 2004 or later better check to see if you have California emissions before replacing parts. I may be wrong about the year but it can't hurt to check before spending money.

guitarfish
01-12-2012, 11:21 AM
Just a note on the California issue. Several years ago PA adopted the CA emission rules for all new cars sold in the state. If you have a vehicle 2004 or later better check to see if you have California emissions before replacing parts. I may be wrong about the year but it can't hurt to check before spending money.

That's good to know going forward. They don't do emissions testing in the NE part of the state where I live. Even if they did, according to Magnaflow, the cat should perform as required.

I've driven about 300 miles and a dozen trips since resetting the SES light. Still walking on eggshells, but hopeful.

PA adopted these for 2008, btw:
Pennsylvania Adopts the California Emissions Standards for Automobiles (http://apps1.eere.energy.gov/states/news_detail.cfm/news_id=10285)

jpb53
01-12-2012, 12:31 PM
Article in the link. Aftermarket Catalyst Terminology by Mike McCarthy.
http://repairnet.aircare.ca/documentation/newsletterpdfs/2009-1.pdf
This explains some of the myths about converters.

rickisrad
01-15-2012, 11:41 AM
Replacing the upstream sensor would decrease the possibility of too much fuel and a rich condition. You may have to purchase an O2 emulator from ZZP to eliminate the light entirely if you are unsuccessful in finding the issue causing the light to come on.



the o2 emulator will not work on our generation. buy a reprogrammed pcm from zzp or elsewhere and have them program out the code! $129 no code and faster car.

guitarfish
01-16-2012, 06:17 PM
Well I seriously give up. After 700+ miles of driving with no SES light, it popped on after I started my car tonight at work. Scanned it again, the P0420 is back - catalyst efficiency below threshold. With new O2 sensors pre and post, plus a new cat, what's left?!?!

rickisrad
01-16-2012, 07:08 PM
do yourself a favor and get the reprogrammed pcm with the code p0420 and or evap codes deleted from zzp or one of the other performance stores http://www.automotiveforums.com/vbulletin/showthread.php?t=976388. there has been issues with aftermarket cats with our generation grand prix. this is the best fix if you are not having any drivability or power/ fuel mileage issues. I believe they are available for the 2008 model? e-mail them and ask

guitarfish
01-16-2012, 07:11 PM
do yourself a favor and get the reprogrammed pcm with the code p0420 and or evap codes deleted from zzp or one of the other performance stores http://www.automotiveforums.com/vbulletin/showthread.php?t=976388. there has been issues with aftermarket cats with our generation grand prix. this is the best fix if you are not having any drivability or power/ fuel mileage issues. I believe they are available for the 2008 model? e-mail them and ask

I think that's the best option Rick. If I were having engine performance problems, I'd think it would show up somewhere - oil loss, misfires, poor mileage - something.

rickisrad
01-16-2012, 07:14 PM
I think that's the best option Rick. If I were having engine performance problems, I'd think it would show up somewhere - oil loss, misfires, poor mileage - something.

I agree. you will be happy with the added performance also.

guitarfish
01-16-2012, 07:15 PM
How does it help as far as performance?

rickisrad
01-16-2012, 07:18 PM
it has adjusted timing and a bunch of other modifications. works even better if you have a CAI. here are some changes done to the pcm....

FEATURES:
•Speed limiter removed
•Raised rev limiter
•Raised shift points
•3-1 and 4-2 skip shifts
•Programmed for race pellet added timing
•Transmission line pressure increased
•185F fan turn on
•90 second fan on at key-off (this feature activates when engine coolant is 180 degrees or greater)
•MAF calibration is year specific
•WOT fueling richen to reduce KR
•Removes lag by changing downshift tables
•Correct VIN number programmed in (if put in note section)
•Part throttle KR issue fixed
•Torque abuse modes are modified to eliminate bog at launch
•Shift KR is remapped for modified vehicles
•Power enrichment tables modified for cars running increased boost
•P0128 code removed for running drilled or 160 Tstats on newer cars
•Torque converter lockup tables modified to improve transmission life and eliminate converter lockup hunting
•Fiero PCMs have all codes deleted for use in the Fiero, 1.0 features, security disabled, ABS disabled, etc (use the year of your engine on the drop down and all 9's for a vin)
•Sand rail PCMs have all transmission settings disabled, all codes deleted that need to be, security & ABS disabled (use the year of your engine on the drop down and all 9's for a vin)

guitarfish
01-16-2012, 07:22 PM
What's a CAI?

rickisrad
01-16-2012, 07:28 PM
What's a CAI?

sorry Cold Air intake

guitarfish
01-26-2012, 02:03 PM
Things are finally starting to make sense.

The Magnaflow cat I bought, 24205, is considered a “standard” converter, as opposed to the Magnaflow 49227 which they call an “OEM” grade. The 24205 simply doesn't have the required precious metals to handle the load of a CA emissions vehicle, which explains the recurring P0420s I've been getting.

The 49227 is technically a 49-state cat, however they do specify that it is the correct cat for a vehicle with CA emissions, as long as the car isn’t registered in CA. Because many cars outside of CA now have CA emissions, but don’t require the certification, they sell the same cat, without certification, for less money.

For comparison purposes, I also looked at the Walker 54752, which they call an “ultra” converter. Walker says it's also the right converter for a car with CA emissions, as long as it’s not registered in CA.

The Walker has a 25K emissions warranty, and runs about $240. The Magnaflow has a 50K emissions warranty and runs about $380. I asked Walker how long I could expect their relatively inexpensive cat to last, and the rep said, “well, the warranty pretty much tells you how long it will last.” By comparison, he said the GM cat warranty is 80-100K, which is why it costs so much more (about $850).

Here’s what I find most interesting: in all the reading I did, all these companies are saying “CATs don’t fail by themselves!” and that you have to find the underlying reason why they failed, or they’ll keep failing in your car. Yet, it sounds like they know a cheap $225 cat is going to die in 25K miles, but the ones with the longer warranty will usually last longer. This pretty much shoots holes in what they’re saying about cats not failing by themselves.

I've been driving around for the last week with an ODB-II scanner hooked up to my car, watching all kinds of parameters. I'm pretty confident my car is running as it should, bad converter aside.

Well, now that I finally understand this, I’m planning to purchase the Magnaflow 49227. I need to keep the car for another 75K miles, so it’ll be interesting to see how long it lasts.

DeltaP
01-26-2012, 05:11 PM
Beware of aftermarket cats. Alot of em, especially the cheapos wont work for very long and you'll find yourself back at square one. They cant handle the volume. The OEM's are the best. Or look into a quality one made by Walker,Magnaflow,etc. Best to change both O2's when replacing the cat. They do wear out. HTH

rickisrad
01-26-2012, 05:14 PM
get the zzp downpipe and high flow cat with the corrected o2 for 2006 and up and be done with it. and or see if they can get a pcm programmed for you to eliminate this.

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