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Is there a light you are looking for ?
Sorry, try this.
above the tach gauge, it looks like a guage with a pointer and an arrow pointing down
The one I highlighted or circled?
1 light over from the hi beam indicator to the left
That is a green cruise control light.
What is the arrow that points down when comes on. It is comming on without the cruise on and it defaults to a limp home mode?
ok, maybe this is a different light. Does your cluster look exactly like this one.
Yup, what would make it come on without the cruise set and go into limp home mode?
That is the strange part. That light should only come on for cruise. It is green? but you say there is another arrow?
Forget the arrow, Any ideas why it comes on without the cruise set and when it does it goes to low power?
That sounds like a glitch in the system them. Does the check engine light come on?
Yes, when you are at highway speeds and you accelerate hard it the green light comes on first then the check engine light, you stop and idle or shut it off and will reset untill you do it again
OK, that may be the fuel pressure. This is the Duramax?
There is a common issue with these engines. It is the fuel pressure relief valve. This valve is a small plug in the end of the drivers side fuel rail. When they get hot, the start to open a bit too soon and set this code. There is a cheap solution to this. A shim that will hold the pressure back. Here is a website that sells these shims. http://dmaxstore.com/index.php?main_page=product_info&products_id=93
You are welcome.