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Discussion Starter #1
So, I'm running into quite a problem right now. I've been to two separate mechanics now and I'm being told two different things. I have a 2006 Colorado Crew Cab, 2.8L automatic... Bought it brand new July 4, 2006. All work done to has been funded by myself so I know what has been done to it.

The first place I went to was Firestone. I had them do a diagnostics on my truck. According to their recommendations, I need to have my rear catalytic converter replaced.

The second place that I went to, Maximum Automotive (local here in Naperville, IL). Their diagnostics check was was that, because there's only one O2 sensors (located after the 2nd cat), that my best option would be to replace both catalytic converters. If I do end up replacing both, it would run me around $2200, something that I can't quite afford.

My question(s) are... how many O2 sensors are there on these trucks? I thought I read somewhere that there should be one O2 sensor per catalytic converter... one for the front cat, and one by the rear cat.

Can someone shed some light on this please?
 

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Damn !!! I hope someone chimes in that knows such things !!! That is a lot of change to drop not knowing for sure what the gremlin is !!! Hope you find the little bastard and choke him to death !!!:lol2:
 

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Discussion Starter #3
I'm hoping that someone chimes in too! Once I find that little bastard, I'll be sure to torture his ass just like he's been doing to me.

I just bought 4" lowering blocks, 3" lowering springs... and not to mention brand replacement leaf springs since one of mine is currently busted.
 

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What is driving you to get diagnostics checks? Are you getting a "check engine" light? If so, what are the DTCs that are set? If the exhaust system has not been modified you will have two O2 sensors. This link has a diagram of their locations (items 7&14): EXHAUST SYSTEM | Nalley Buick GMC Brunswick Shops always try to sell converters. Easy money.
 

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I recently did away with my exhaust manifold which is where the first cat is located. The only o2 sensor I have connected is the one upstream from the first cat. I took the second one out all together and still haven't thrown a code. I replaced the exhaust manifold with a JTR header, which is way cheaper then buying a replacement, and it's awesome. Sounds better and performs better. The only important o2 sensor is the one before the first cat coming out the engine. Not sure if this helps. Just my recent experience.
 

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Discussion Starter #7 (Edited)
What is the actual diagnostic code(s) being displayed on the code scanner? That's the place to start. There's an O2 sensor on each catalytic converter.
I don't have the paperwork handy right now. I just tried to find it, but when I do, I'll be sure to post the code.

If I am supposed to have 2 O2 sensors, then I'll need to check the connections with the first sensor since it's not being read and the 2nd shop didn't even know it existed. Is this hard to do?

The code that is being is P0420 - Cat Efficiency Bank 1
 

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Is the truck operating normally, except for the "check engine" light? It's hard to believe that the 2nd shop that you went to couldn't find 2 Oxygen sensors and are telling you that the first sensor is not being read. The ECM uses the signals from the first O2 sensor to set the fuel ratio. If the ECM is not reading the first O2 sensor, you will definitely get a DTC regarding that. The second O2 sensor is the one that ECM uses to determine Cat Efficiency. The ECM compares the readings of the two O2 sensors to tell whether or not the converter is operating within limits. Your problem may be nothing more than deteriorated O2 sensors. How many miles on your truck? O2 sensors are supposed to be replaced at 100,000 miles.

Did you look at the link in Post#4? Item #14 is the #1 O2 sensor. It is screwed into the exhaust manifold.
 

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Discussion Starter #9
I have roughly 180,000 miles. I'm thinking I'll I to autozone and buy the o2 sensor and replace it. Shouldn't be hard, right?

And yes, the truck runs great other than the CEL light that's stays on. I have noticed on several occasions that the light will go off for a day or two and then come back on.

Any special tools needed to replace the sensor? I noticed easy access to the sensor from above so shouldn't be too hard to get to. What's the torque for tightness when replacing?


Sent from AutoGuide.com Free App
 

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If you have the budget, you should replace both sensors. If not, at least replaced the 2nd one. It is known as Bank 1 Sensor 2 in case the store asks. I would suggest that you look at the installation of the sensors to determine what tools you will need. Quite often you will find that you need an O2 sensor socket that is sold most anywhere. I think most of the sensors are 7/8". If possible, go with brand name sensors (Bosch/ACDelco/Denso) as they are more reliable. The torque on the sensors is 31 ft/lbs. If you are going to torque them, you will most likely need a n O2 sensor socket.

Make sure the new sensors have anti-seize compound on the threads. Most do.
 

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With 180,000 miles you're long overdue for new O2 sensors. Replace both of them. You should use a 7/8" (22mm) O2 socket, but a 7/8" open end wrench works in a pinch.



The O2 socket from Harbor Freight is $7.
7/8 in. Oxygen Sensor Socket

The crows foot style o2 wrench works well...


02 sensors can be a bear to get off sometimes. Be sure and spray the old 02 sensors with some penetrating oil before you attempt to remove them.
 

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There are indeed two sensors.

Do not ever take your truck to those two shops again. Never take any vehicle to Firestone.

Alldata shows .7 hours to replace both sensors so $70 labor. Both sensors should run you less than $100 @ Rockauto.

Advance Auto parts is usually cheaper than Autozone since they always have coupon codes available.
 

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With 180,000 miles you're long overdue for new O2 sensors. Replace both of them. You should use a 7/8" (22mm) O2 socket, but a 7/8" open end wrench works in a pinch.



The O2 socket from Harbor Freight is $7.
7/8 in. Oxygen Sensor Socket

The crows foot style o2 wrench works well...


02 sensors can be a bear to get off sometimes. Be sure and spray the old 02 sensors with some penetrating oil before you attempt to remove them.
Yes, I use a small propane torch to heat the bung up before I remove the O2 sensor.......they come right out everytime.

Yes, again I agree with Rich.......at 180K, your due for new O2 sensors.

I did both of mine I think for under $100 with new DENSO sensors. If you do those and the problem does not go away gut the first cat for free. If that doesn't fix the problem replace the secondary cat.

The good thing is all of these task/job are easy to do.......I did them all in my driveway/garage
 

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Keep us posted. Even if replacing the O2 sensors doesn't correct your problem, it won't be a waste. You were way overdue anyway.
 

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Yeah I do my O2 sensors every 100k
 

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I replaced my O2 sensors at 130K.

The resulting improvement in driveability, power, and idle smoothness made me feel like an idiot that I hadn't done it long ago.

One pro mechanic told me that most O2 sensors are good for only about 60K.
As far as I'm concerned, given how simple they are to replace and no more than they cost, I'll be on it at 50 to 70K every time in the future.
 
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