[shawnner]

We have the same car - 2006 w/ L4 - and engine light problem. My mechanic has tried several times to repair and couldn't - then took to to the Pontiac dealer & still no repair.
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I took my car to the garage to have front wheel bearings replaced and check why the "check engine" light was on...Since my car was running perfectly, I thought maybe due to hitting 60k that it wanted routine maintenance.

Garage said my computer "quit communicating" so he re-programmed it. Since picking it up, my mileage and power are both down 25%...then the engine light went back on. Took it back, he reset it and cleaned the fuel line (rail?). But, same problem w/ mileage & power.

I have a 2006 G6 w/ 4 cylinder... used to get up to 34 @ 65mph down a flat highway and 26 mixed driving. Now 18 mpg in mixed driving.

 

[shawnner]

After several trips to the dealer and the light continues to come back on (saying misfire code). My light has now gone out and has been out for a week - but still poor performance and poor mileage (25% reduction in both).

The dealer now says I have a bad cat conv and can be replaced under the 80k warranty for free. I doubt this will fix my problem, but at least it's free.

 

[shawnner]

thinkin it could be the cat conv

The more I think about how the engine "feels" and sounds when accelerating it could be a restricted cc. Hoping that helps & will post results here. Now, it's been on order for over a week with the dealer...so, just waiting. It does give me an excuse to ride the Harley pretty much everyday tho.

 

[shawnner]

The dealer replaced the Cat Convertor for free under their 80k warranty and BAMMM... I'm back in business! It worked... mileage back to 32 hwy / 28 mixed & runs strong - these L4's have the feel of a V6... happy again! Actually quite surprised....

Now, just to make it more confusing, I'm not sure what to believe. The dealer claimed that my first problems (read above) were the original problem with the car and the CC went bad in the process of those repairs... I think he wanted to be sure I'd pay for $600 worth of "other" repairs. My guess is that the CC was casing problems all along since nothing else they did made any difference.

 

[shawnner]

check post on 06 g6 big problems for update

by the way my cat was not clogged just malfuntioning so the o2 sensor was reading the wrong signals making bad adjustments, no warranty but new cat was free so im assuming a few cars have has this problem(when i mentioned bad running g6 they instantly said cat lol) they also told me it was clogged lol but babying it over to the dealer.... after 4 miles of barely gassing it at 20 it started to get better, alot better, but another 2 miles of flooring it it started getting less and less power and gradually acting up more. went back and forth a few times like this till i got there, by the way it wasnt like turning on a light switch power gain was gradual and loss was gradual it just depended on if i drove it 1/3 trottle or laid into it a bit

i just read this again & had to tell you...my problem felt very similar (almost ok when babied, but straight to heck when pushed evn a bit)

 

[shawnner]

UPDATE on engine light...
The Cat Converter was replaced & the car has been running well... BUT NOW the check engine light has now come back on, very slight engine stutter from time to time, but only a slight difference in fuel economy. The lights goes on & off every 500 miles. I'm not going back til something falls off this thing... don't know what to think