GM 120 Point inspection for used car certification? [Archive] - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

: GM 120 Point inspection for used car certification?

01-20-2007, 03:08 PM
Does anyone have a list or know where to find a list detailing the items that GM/CHEVY checks on their "120 point certification inspection"? The reason I ask is that less than a month ago I bought my 05 TB Lt and from the very beginning I have been getting around 11.5 mpg calculating at the pump. The OBD agrees with this as well and read an average of 11.9 mpg over the last several tanks. I want to know if any fuel system issues or tuning for it to run less rich is part of that inspection. I traded in my 4runner because it was getting below 13 mpg and I was told at the dealer and by several friends who drive 05-06 TBs that they were (even in the winter) getting 15+ mpg around town. So now I replaced my old truck and am actually getting worse mpg?! I know we dont drive our TB's for gas efficiency, but only being able to get to around 250 miles on 22 gallons of gas sucks a a lot.

I just want to know what I can demand from the dealer to look into this and solve it if there is an actual problem causing this. The car is still under factory warranty and I did buy the extended warranty as well.

Funny thing is that I asked them to look into this when they were finishing the inspection (about a week and a tank of gas after I bought it) and they did not, then about a week later after I ran another tank or so through I called and talked to the sales guy there who said he was going to work it out with the service dept. to get it looked at and he never called back.

01-21-2007, 01:58 PM
I take others people's gas mileage claims with a grain of salt. Is their definition of "around town" the same as mine? Is part of that freeway driving or is a large portion sitting idling in traffic.

Were you drive and HOW you drive makes a difference too. Weather conditions, different brands of gasoline and gasoline blends all contribute to your gas mileage or lack thereof.

If you look around, we have had NUMEROUS discussions about gas mileage on the freeway in this forum. Some claim as low as 15, others 28! (Yes I said 28) Too many variables to pin point - including the exaggeration factor.

I bought mine new so I have no idea what the "120 point certification inspection" includes. Sorry, maybe someone else will know the answer to that question.

You didn't say how many miles is on your vehicle - many of us noticed that these SUV's seem to get better mileage with age. Especially after about the 15 - 20K point. Mine 05 EXT has about 31K on it, and is currently getting about 12 - high 14 around town, just under 20 on the freeway. The 12 comes from taking the kids to school and sitting in traffic a lot!

01-21-2007, 02:47 PM
:( Hey, don't be dissapointed! I also believe that the gas mileage will get better with time. Don't go by what the dealer, or the sticker says.

The GM check...they don't look at gas mileage, they just check the physical aspects of the vehicle. The OBDII system verifies that the vehicle is running correctly, and if not, the system will kick on the check engine light.

Driving conditions are a big factor, and you will learn the vehicle the longer you own it. I've go just over 3K on my 06LT I6, and my around town is between 11.5-13.0mpg. the shorter trips will bring these numbers under 11.0mpg! Since new, I've only seen a top mpg of 16.5-17 on the hwy. I kind of expected that when I bought the TB. Keep in mind it's a I6 with almost 300hp driven by only a 4 speed auto.

Part of the check should have been the condition of the air cleaner, which will affect mileage! Check it yourself and verify it's condition. Keep in mind, the tech may reccommend services when checking the vehicle, but the used department don't like spending the $$:duh: !!

Doc Brown
01-22-2007, 09:59 AM
I live in Milwaukee. I think you guys are stuck with the same gas we are. It's winter. I took a trip to Janesville over the weekend. I only got about 15 on the freeway. I'm getting only about 12 in day to day mixed freeway/street driving. In warmer weather I get about 17.

01-22-2007, 12:12 PM
Thanks everyone! My 05 TB has 33k on it. For fuel economy reasons my wife and I both drive it like Grandmas. Rest-assured I did look at the other fuel economy threads before I posted this one, but did not see anyone reporting 11.5 or below which was why I was concerned and wanted to bring that particular mpg issue to light as it relates to the dealers responsibility for the delivery of the car. It sounds like in the winter with the winter grade I am of course not the only one getting extremely subpar mileage. I always factor in that there will be a difference in the winter, just not as big a difference as there seems to be.

Doc Brown - Is the 17 mpg you report in normal (non winter) weather mostly around town (read as "very little - no highway") ? That is what a friend of mine was reporting and what I was expecting when I bought the TB, however he has also since informed me that his 18 around town is lower now around 13-14 in his 06 LS

01-22-2007, 12:45 PM
The official EPA numbers, which are generally overly optimistic on SUVs, are 15 City and between 20-21 highway for an I6 equipped 4x4 SWB model. Consumer Reports averaged 15mpg in their economy mix, that includes a short highway/suburban run....the XL/EXT models faired worse at 13mpg in their test. Don't know their test conditions, but I do know that short trips or stop & go with a cold engine kills the fuel economy in my Envoy. Admittedly less so now then when it was new, between the motor breaking-in (which ranges from 3,000 to 30,000 miles - some are tighter than others), the exhaust, intake and tune its up noticeably. I remember my first couple of tanks averaging around 12 mpg in the same driving that now yields around 16 on average.

As far as the 110 point CPO checklist (its 110 for Chev, GMC, Pontiac & Buick), you can find it here: (Click on the dot for Checklist under the center of the Envoy pic)

Other things to keep in mind are that some brands of gas perform differently, especially if they're 10% Ethanol, which yields less power and economy. The winter grade stuff isn't great for economy and the ethanol junk is worse. A whole lot depends upon the driving conditions, tires as well as pressure (some roll easier than others), gearing (the 3.73 & 4.10 give better city mileage than the 3.42s btw) and a host of other things you may not be able to control. First thing I'd try is to switch brands of gasoline, try a Top-Tier brand for a couple of tanks and see if it helps. (GM as a published list of Top-Tier gasoline, easiest to find is usually Shell).

01-22-2007, 12:51 PM
Don't know about the gas types, I have never seen 11.5 even pulling a 2000 lb. trailer. Worst I ever saw was 15. Something's up!:confused:

01-22-2007, 02:54 PM
i know you said youre driving like grandmas- but how?
I ask because I was with my GF... she has a 98 Civic. she tends to tap on the gas alot....
when she drove my Trailblazer- I nodded off- and in my slumber- I could feel my head bobbing back and forth- after a bit of this bobbing- I opened my eyes and said- WHY ARE YOU DOING THAT?
she looked at me..... I said- theres no need to keep keep pressing on the gas like that- all your doing is wasting gas cause you just bring the RPMS up and literally accelerate, slow down. accelerate. slow down....
I told her to use Cruise or just keep steady pressure on the gas pedal... told her its a no- no to keep tapping it like that... well its a no-no that will empty your pockets.
This past weekend I was trying to teach her how to drive to get best mileage in city- (since she plans on getting a V6- Impala)....
I dont remember if I mentioned- but did you leave your recirculate button on?

01-22-2007, 04:08 PM
Give your TB a little more time to 'learn' your driving style. It took my envoy about a month and gradually went from 13 mpg (what my 97 suburban was getting) up to 18 mpg currently. I bought mine from my company, Enterprise Rent-A-Car, so it was a prior rental with hundreds of people driving it so the computer never really learned a driving style to adjust it's settings to. Chances are your TB was a prior rental (what they call program cars) and is going thru the same learning process.

As for certification, what we do is a similar process, and what it is designed to do is ensure that the customer can get thru the next few service intervals (oil changes) with out having to do any other maintenance. So not only is everything legal and safe, it also has some decent life remaining. Our cert. is backed by GM so chances are their's is similar.


01-22-2007, 04:13 PM
hey guys- you thinks its possible for him to disconnect battery so that the computer forgets driving style ? and relearns his 'gas saving style?'....
just like disconnecting battery erases those learned settings for the throttle body?

01-22-2007, 04:48 PM
If the battery is disconnected, it is possible that the gas mileage will get worse before getting any better:no: . If it's already "learning" his driving habits, this would be a step backwards. But it may help, if the previous owner drove very differently:undecided . A GM tech could probably tell you by comparing the short term fuel trim to the long term fuel trim; among other parameters

01-22-2007, 05:26 PM
hmmmm interesting.
well, he could make it forget. and then drive it like if it were 'new' and have it learn his style....
if it was a rental. and you know some people abuse the cars...

01-22-2007, 06:07 PM
More like beat the Crap out of rentals...good point.

Hey Cutup8144, did you run a carfax on the TB to see who owned it before?

Doc Brown
01-23-2007, 01:32 PM
Doc Brown - Is the 17 mpg you report in normal (non winter) weather mostly around town (read as "very little - no highway") ? That is what a friend of mine was reporting and what I was expecting when I bought the TB, however he has also since informed me that his 18 around town is lower now around 13-14 in his 06 LS

Its a combination, but keep in mind, my freeway driving speeds vary from 25-75mph. Thats due to 5pm traffic. Like Blueblazed said, its going to be different for each individual driver. When I drive harder (faster and more agressive) my mileage sucks. When I glide a lot and drive at moderate hwy speeds (60-65) I get pretty good mpg. Right now, at $1.95 gal, I'm not being as careful as I could. So getting only 12 is mostly due to that. Last winter I was getting 15 without trying hard. Again, not mashing the pedal and letting it glide whenever possible.

01-23-2007, 03:02 PM
1.95..... were still at $2.40 here in Los Angeles

01-23-2007, 11:59 PM
More like beat the Crap out of rentals...good point.

Hey Cutup8144, did you run a carfax on the TB to see who owned it before?

Yup, sure way I would have bought it without it!

I talked to the dealership and supposedly they are going to get back to me about a time to bring it in once they determine how to address the problem...they say they have never seen 11.5 mpg on a TB. They said they are looking for a way to test it and see what is wrong...I think they are stalling...I am gonna keep in touch almost daily until they get it in there.