Thread: P0420 and O2 drama

2005 GP with Gen3 3800 @ 170k mi. It uses 1 qt. of oil every 3k mi. since about 100k. I JUST replaced the LIM due to failure, but I have done the water pump and coolant elbows a few times in the last few years. Everything FINALLY looks good to go with the coolant system, but the damn thing still smells like coolant. Hope there isn't a small head gasket leak or something.

Anyway, last year I replaced the upstream O2 sensor with a Bosch along with NGK iridiums and quality wires as part of regular maintenance. It ran perfect for about 6 mo., then I got a CEL that indicated an O2 sensor issue, though I don't recall the exact code. I'm almost positive it pointed to the front sensor as I sent the "new" O2 sensor back to O'Reilly via my wife for a replacement and they stated that they couldn't find that p/n associated with any similar GM vehicles. Not sure where they pulled it out of their butt from last time, but they sent home a different Bosch sensor. After coming up empty handed on the internets, I called Bosch and had them confirm the part number issue, and again I don't really recall the specifics, (it's been a crazy year for motorcycle, vehicle, and home maintenance) but I THINK they were generally worthless. It was enough encouragement to go ahead and use this new p/n, however. I'm not one to just throw the wrong part in, so I must have been satisfied with this sensor when I last slapped it in.

Well, that was about 6 mo. ago and today it threw a P0420 Bank 1. I either have the wrong sensor again, something it making it fail every 6 mo., the downstream sensor now needs replaced, or that 1 qt. of oil every 3k mi. has finally damaged the cat and or sensor. I run a can of Seafoam through the brake booster line every 50k or so, and 1 can in the gas tank every 20k or so. I JUST did this process via brake booster about 4k mi. ago along with the LIM.

I'm thinking about replacing the downstream sensor and going from there but wanted to run this issue by you guys. I'm not even positive which bank is 1 and which is 0, or 2.

Bosch is Junk. Go with ACDelco or Denso.

P0420 is a downstream code so either the cat is shot or the sensor or both.

I'm advised by a VERY reliable source that Bosch is the ONLY way to go with O2 sensors, and to replace them every 60k mi. for ideal performance. Not trying to argue though, but you definitely lost me with the AC Delco thing. IMO, ACD is junk across the board with the exception of the coolant elbows. I do like me some Denso plugs though. I did come here asking for opinions though and appreciate yours.

I will start with the O2 sensor. Somehow I have yet to have to purchase ramps, (all 4x4 trucks, really) so I'll prob. wuss out and pay the Ford stealer to swap it during this oil change. If that doesn't get it, I'll probably get a Magnaflow Spun Cat from PlanetMagnaflow to slap in there, unless the O2 bung is in the middle of the cat instead of aft. Does anyone know the pipe diameter for an NA Gen 3? Should I consider an alternative cat?

AC Delco is stock oem so you will be better off with them

Originally Posted by Jackal

I'm advised by a VERY reliable source that Bosch is the ONLY way to go with O2 sensors, and to replace them every 60k mi. for ideal performance. Not trying to argue though, but you definitely lost me with the AC Delco thing. IMO, ACD is junk across the board with the exception of the coolant elbows. I do like me some Denso plugs though. I did come here asking for opinions though and appreciate yours.

I will start with the O2 sensor. Somehow I have yet to have to purchase ramps, (all 4x4 trucks, really) so I'll prob. wuss out and pay the Ford stealer to swap it during this oil change. If that doesn't get it, I'll probably get a Magnaflow Spun Cat from PlanetMagnaflow to slap in there, unless the O2 bung is in the middle of the cat instead of aft. Does anyone know the pipe diameter for an NA Gen 3? Should I consider an alternative cat?

HAHAHHAHAHA!

I knew you were going to be a Bosch lover. Uneducated people think "oh, Robert Bosch invented o2 sensors so I'm gonna get a bosch cause they are the best" lmao.

Bosch is junk on GMs. GM uses Delco, Delphi, and Denso for their o2 sensors because they will last 100k miles provided the owner maintains the car properly. If your "reliable" source says bosch is the best and recommends changing every 60k miles for best performance, that source is a jackass. Also if he was so reliable, you wouldn't be second guessing and asking questions on here.

You wouldn't need to change a Denso, Delco, or Delphi that soon for "best performance". Bosch is not the "ONLY" way to go with o2 sensors.

I'm sure you'll be offended by my post but remember you said you wanted "opinions". Delco, Delphi, and Denso are the way to go on this platform.


Why would you go to a ford dealer?

changing an o2 sensor is extremely easy and so is an oil change.

in most cases high flow magnaflow cats cause a P0420 code so like Ice said, get the code tuned out or do the anti-fouler trick.

The Maggie Spun Cats are actual converters, supposedly more efficient, but I didn't believe it till I replaced all 4 on my 01 F-150 with longtubes and 2 spun cats w/o tuning them out. I like them because they are small, light, cheap, and stainless...and weld right in. Open to inexpensive suggestions though. Are the stock cats even known to fail this "easily"?

Going AC Delco certainly would take the guess work out wouldn't it... How do they compare in price? Seems like the Bosch sensor for this was about $75.

Also, it's best to replace both o2 sensors at the same time since they work together and doing that will give you optimal performance.

Originally Posted by HighOctaneRacing

HAHAHHAHAHA!

I knew you were going to be a Bosch lover. Uneducated people think "oh, Robert Bosch invented o2 sensors so I'm gonna get a bosch cause they are the best" lmao.

Bosch is junk on GMs. GM uses Delco, Delphi, and Denso for their o2 sensors because they will last 100k miles provided the owner maintains the car properly. If your "reliable" source says bosch is the best and recommends changing every 60k miles for best performance, that source is a jackass. Also if he was so reliable, you wouldn't be second guessing and asking questions on here.

You wouldn't need to change a Denso, Delco, or Delphi that soon for "best performance". Bosch is not the "ONLY" way to go with o2 sensors.

I'm sure you'll be offended by my post but remember you said you wanted "opinions". Delco, Delphi, and Denso are the way to go on this platform.


Why would you go to a ford dealer?

changing an o2 sensor is extremely easy and so is an oil change.

in most cases high flow magnaflow cats cause a P0420 code so like Ice said, get the code tuned out or do the anti-fouler trick.

Well, you called me uneducated so you can pretty well go fk yourself, but I'll take some time to respond I suppose. This guy is THE Ford modular tuning guy and has been consulted by Rousch a time or two, and has even been brought in to train their techs. I don't expect you to buy it though, don't care really. Just stating my reasoning for doing so. It's just a sensor that reads a "precise" voltage, so I think a quality sensor is a quality sensor regardless of Bosch or Denso manufacture. I would, however, prefer a Denso plug as I stated, over a gimmicky Bosch plug. I didn't come here to debate sensor or plug brands though, so you're wasting your breath trying to sell me on your preference. I use Ford dealers because all of the local GM shops are known to be **** and I'm a Ford guy anyway. I also really like Motocraft, including their oil and filters. I get a discount so I can't buy the **** myself and waste my own time cheaper than just taking it to them to deal. It's the only thing I trust a dealer for other than inspections and tire changes.

I just paid 30$ for an ac delco o2 sensor on amazon. only did the front one, didn't realize I was supposed to do both at the same time.

Originally Posted by HighOctaneRacing

Also, it's best to replace both o2 sensors at the same time since they work together and doing that will give you optimal performance.

They actually work independently. Each sensor providing vdc to the ECU to interpret. Christ, UNEDUCATED people. I forgot to mention, he recommends 60k replacement on the upstream only, and downstream as they fail...the downstream only reflects cat performance while the upstream, of course, helps dictate AFR.

Originally Posted by SgtMarshal

I just paid 30$ for an ac delco o2 sensor on amazon. only did the front one, didn't realize I was supposed to do both at the same time.

You aren't, but that's just my uneducated opinion. Seems like these Denso sensors are CHEAP. Maybe that's why our ACD/GM Obama supporting fanboy like them so well?

Hahaha...alright I'm done.

Originally Posted by Scottydoggs

i wouldn't say uneducated, but you sure dont know your grand prix very well yet.

these cars just dont like anything but oem sensors. aka delco stuff. has nothing to do with the aftermarket parts in a whole. your gp will just not like em.

i dare you to go use anything other then a delco maf. most the cars never run right, or runs good for a week then craps out. and your out that money cause you bought a aftermarket sensor for a car that hates them.

search rockauto for your new sensor. cheapest place ive found for ac delco parts.

I suppose I can see that, thanks for taking the time. You are right, I do as little as possible with the GP as it's my wife's beater.

That explains everything, You're a ford guy. Roush is a joke. If he cared about winning like Hendrick, he would run Chevy's and pay better to keep drivers.

You sure sound like you don't really know how to work on cars but that's cause you're a ford guy lol.

Sure I could go f uck myself but I'm not going to hence why I'm not buying bosch crap.

I don't need to "sell" you my preference. I don't give a rat's ass what you do to your car because it's your car. I was just giving you real world information on these cars and what o2 sensors they prefer.

Here's my new preference to you. Buy Bosch and keep f ucking yourself.