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I have a 2005 Z71 Colorado Crew Cab with 148,000 miles on it. I have taken good care of the care with all tune ups on time and I run Mobile 1 oil only. The gas mileage has taken a nose dive and the engine is running rough. Also my engine light and ABS light is on. Before I take it to the dealer for service has anyone had the same problems? I always take it to a dealer for service but I want to get an idea of what I may be getting in to so I don't get my wallet cleaned out. Its a great truck and I want to keep it until it no longer runs. This is my 3rd chevy that I have put many miles on and it seems like these problems always happen at high miles. I have been looking at different forums online and I can do a few things first like change filters and plugs and clean the mass airflow sensor. I'm going to do that and see what happens. Next will be the auto parts store for a code scan and see what comes up if there is no change.

I called GM and spoke to a customer service rep named Gina. She told me about a known issue with the exhaust valves and GM issued a dealer bulletin about it. GM extended the warranty on the parts to 100,000 miles. I never received this information at home. It would have been nice to know this 48,000 miles ago. I was told to take the truck to the dealer and have a diagnostic test performed to see if this is the problem. She then told me if there is a problem with the head GM and the dealer may be able to work out something to help me. If GM knows there is a problem with a component of their vehicle it should be taken care of as a recall. I made this statement to rep and I was told that she understood what I was saying but thats the best they can do.

So now the adventure begins and I'll keep posting my progress.
 

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Could be a bad cat. If the light stays on then its a emission issue, if the light blinks on and off then its a engine/trans issue that needs immediate attention before damage occurs. I'm betting on a bad cat.
 

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Hey Steamer, since you're going to be replacing your own plugs you can do a compression check at the same time & this will tell you if your engine has the "exhaust valve" issue that the GM rep was talking about, & you will know ahead of time if they're going to be getting into your wallet a little or a lot. X2 on replacing your own filters. A dirty/plugged air filter will definitely bring your MPG way down.
 

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OK. I went to the autoparts store and plugged in the OBDII reader. I got several codes associated with emissions. They are - EVAP vent solenoid valve control system, Evaporative emission system leak detected, idle speed low.

The guy at the store cleared the code and the engine light went out. After about 70 miles its back on. How do I locate a leak and what could be leaking?
 

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Evap system leak is usually the gas cap seal gone bad. Remedy is a new gas cap.

If you have replaced the plugs and filters (air and fuel) and cleaned the MAF but still get bad fuel economy, try replacing your upstream o2 sensor.

I have a 2005 with 169k miles and still get good mileage.
 

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I concur on the Gas Cap being the source of your EVAP codes. I had the same issue on my 04 Crew Cab I-5. Also, your low idle code is probably caused by a dirty throttle body. I have this issue all the time with mine due to the conditions we operate the truck in. It is not something a fuel additive will prevent. You have to remove the resonator box from the throttle body and clean the throttle shutter and the TB where the shutter closes. I use a good non chlorinated carb cleaner and a lint free rag to do mine. For some reason the TB builds up carbon around the throttle shutter and causes it to not fully close at idle. I will bet that if you watch your tach when the engine is running rough you will see that it is below 700rpm. The I-5 has to idle at 750 or above to stay smooth. You probably only have the rough condition when you are NOT driving above 25mph right? I was having all sorts of issues with mine and after speaking with my dealer, cleaning the TB cleared them all up. I have to clean mine about every 3 months and my mileage stays around 21-23mpg with 181,000 miles on the truck.
 

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I changed the plugs for my own sanity but I cleaned out the throttle body and the truck runs like new. Such a simple thing and yet its so important!! I took the truck to Florida and driving on I-95 at 70+ I still got 20 to 21 miles oer gallon. I'm happy how the truck runs, I know have 170,370 miles on it and its going strong. I have been using Mobil 1 oil since new and I am wondering if I should stay with the current 5W30 oil or go with a heavier grade. No smoke and the truck does not burn it either.
 

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Steamer, I would not change viscosity on your oil. Even with some wear in the engine, the passages and oil galleys in the engine are designed for a certain fluidity and a heavier viscosity oil will change the flow characteristics. Stay with the 5W30 and if you feel the need (I use full Syn oil in mine also) use an oil additive with it. My Dad was an Engineering tech for GM and was involved with the development of the I-5 engine so I have a little inside knowledge of that engine platform. ;)
 

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205,000 + miles and running well. Only issue is my engine light comes on for coolant temperature yet the truck is always in the same range from when it was new. Any thoughts?
 

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224,175 miles and doing fine. I hear a rumble under the car above 30 mph. I've changed the U Joints, and it's the fourth time, and atill hear it. It seems to oscillate at 55 to 60. Could the drive shaft be out of balance? Anyone have any ideas or similar problem?
 

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At 230,380 the truck still runs well and I still hear a rumble under the truck. Not sure what it is yet. I changed the alternator a few weeks ago and that was not fun at all. I think I invented a few new words! I hope the new colorado has it in a better place. I also change the thermostat this week and guess what? It's next to the alternator! Still happy I have the truck!!
 

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Let's see some pics of this truck if you can post some up here that would be great. @Steamer
 

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242,290 mikes as of this morning. Time for a tune up. I had a problem a few weeks ago, my right front wheel bearing failed but I was still able to get to a gas station and have the mechanic make the repairs. I haven't had many repairs done, mostly breaks and the usual things that wear out, but it seems the local guys do a more thorough job and a more complete repair. The 2 times I have taken the truck to a dealer for repair didn't work out very well with things just not right afterward. I'm still very happy with the truck and have seen the new models, it may be time to pass this one down to my son for his first car and by myself a new one!
 

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The I6 engine has that problem, one of the fixes was a new GM software update. It change the temps at which the cooling fan starts and stops.

EDIT: sorry @Steamer this post was to answer your cooling code problem, I answered not realizing that there were posts on page two.
 

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image.jpg
250,000 miles this week and the truck is running well. The serpentine belt was making noise and I just changed it. It was original equipment. Taking on vacation to Cape Cod and hope to do some over sand driving. Next stop 300,000 miles!! Go Chevy!!!
 

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Nice, my 2005 in has 430 000 km and still running pretty well I also had the engine light issue awhile back. Replaced the fuel cap which worked for a short time. Also had my mechanic replace the solenoid vent valve on exhaust system. Found out after it also needed the purge valve replaced, at that point I called it quits and said I'd run at the decreased fuel economy rather than dump more money into it. I suspect it had to do with a "cheap" oil undercoating I had a buddy do, followed by travelling down plenty of gravel roads.
 

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You guys give me hope. My 2005 beater work truck is currently at 232,xxx miles. It is still running really well!

 

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I have a 2005 Z71 Colorado Crew Cab with 148,000 miles on it. I have taken good care of the care with all tune ups on time and I run Mobile 1 oil only. The gas mileage has taken a nose dive and the engine is running rough. Also my engine light and ABS light is on. Before I take it to the dealer for service has anyone had the same problems? I always take it to a dealer for service but I want to get an idea of what I may be getting in to so I don't get my wallet cleaned out. Its a great truck and I want to keep it until it no longer runs. This is my 3rd chevy that I have put many miles on and it seems like these problems always happen at high miles. I have been looking at different forums online and I can do a few things first like change filters and plugs and clean the mass airflow sensor. I'm going to do that and see what happens. Next will be the auto parts store for a code scan and see what comes up if there is no change.

I called GM and spoke to a customer service rep named Gina. She told me about a known issue with the exhaust valves and GM issued a dealer bulletin about it. GM extended the warranty on the parts to 100,000 miles. I never received this information at home. It would have been nice to know this 48,000 miles ago. I was told to take the truck to the dealer and have a diagnostic test performed to see if this is the problem. She then told me if there is a problem with the head GM and the dealer may be able to work out something to help me. If GM knows there is a problem with a component of their vehicle it should be taken care of as a recall. I made this statement to rep and I was told that she understood what I was saying but thats the best they can do.

So now the adventure begins and I'll keep posting my progress.

I know this is old, but the throttle body cleaning is straight up the issue. Best to just take the throttle body off and clean it entirely.
 
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