Oldblue

Please let us know what cures the problem

Stockerhhr

So finally got around to try and fix the over posting code I changed the bypass valve to the forge replacement and now have a cool sound but still over boosting running about 20lbs for about 3-4 seconds then cuts out and goes into limp mode

RJ_RS_SS_350

If I understand it correctly, the bypass valve could cause an underboost, but not an overboost. It seems quite often the problem has been the wastegate solenoid, AKA boost control solenoid. I just went thru this myself. I had to find a solenoid, because you can't get the part as a standalone.

I got a good deal on a used turbo, with the solenoid still attached, but my backup plan was HERE look at post #8. Problem solved. Another cause that I found others had was the electrical connector for the solenoid had been heated up by engine heat and had become brittle and fell apart. The solenoid is attached to the turbo by a T30 torx screw, it has 3 vacuum(pressure) hoses and the elec. connector.

Stockerhhr

Thank you ! One more area it could be and hopefully that's the issue!

HHR5678

If he has a Trifecta Tune with infiniboost option boost pressures exceeding 20ish PSI with OEM senders will trigger the overboost gate stuck open code. Stocker, When you press the CC steering button, do you see Cruise Control show on the DIC? if no, You may have the same tune.
Here is what I did to live with it, picked up a Turbo smart Compaq BOV and disabled the code from appearing again(software assist), note: avoid turbo surge by adjusting the BOV to mid soft allowing the charge pressure to push the piston and allow recirculate of the gas into the turbo. you can turn the tune on and off via the CC button.

RJ_RS_SS_350

He did say it was bone stock.

HHR5678

Even with a bone stock SS you would not know the Trifecta tune was installed unless you were told it was. Some guys(me) bypassed the GMTU because of all the issues reported. "Stockhhr's symptoms seem to match what I saw happening. The only difference is I know I had a tune installed whereas he is not sure. A simple test of the CC button would reveal if this a Trifecta tune is installed. I believe they are the only ones with this specific feature.

Stockerhhr

So I bought the car seemed to be bone stock can't tellnof it has a tune or not but when I press the cc button nothing comes up on the dic... How would I find out if it had a tune ? Could I just do the sensors and get rid of the codes ?

Dbeluscak

Well...it's either Stealth tuned, or cruise control isn't working properly. Do you notice a difference in performance after pressing the CC button? The difference should be night and day. As far as the overboost goes, changing to 3Bar MAPS will only allow the ECM to see actual boost pressures. Trifecta has been known to work around them by using an algorithm to allow for higher than normal pressures. They make the ECM think it's seeing less boost. The problem is your ECM/tune, if it doesn't like what it's seeing...you end up with ENG PWR REDUCED.

Not to say that your tune or ecm is bad. I don't belive the sensors are going to solve your problem. Inspect all your vacuum lines carefully. There's a lot of useful info over at the cobalt forum. You could even have a "boost multiplier" I'm not sure what they actually call it but it's another way to fake the ECM. I've seen guys use .035 welding tips to restrict flow to the bypass valve, allowing higher than usual boost. Once you reach a certain point, the ECM no longer cares how hard you press the pedal or how fast you want to go. It takes care of the engine first and foremost.

Check out that boost control solenoid mounted on your turbo. Also, who was the previous owner? Or, does it seem like they'd tune it? Tuning isn't for everyone.

Cat Man HHR

The Trifecta tune can be programmed to the traction control button also.