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Discussion Starter #1
17 Terrain 3.6. 58k. Yesterday when i went out to start it up in these frigid Chicago temps i noticed it was running like crap on initial start up. Missing or something. Then saw the check engine light on and the Stabiltrack. Did a onstar diagnostic and it said something with the emissions. The stabiltrack i believe was on because of some snow/ice buildup on the wheels. Had a terrible front wheel shake after running it thru the the car wash last night. Stablink attention thing popped on but today no shake and no stablink light but the check engine light is still on. I know there a threads on this but any ideas what it could be
 

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scan for misfires on each cylinder.
I always recommend a bottle of Chevron Techron Concentrate PLUS
 

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I should also add it seems to come on with initial start up when it is cold and goes away when driving and warmed up. I also notice the coolant resovoir is a little low. Now the coolant isn't just magically disappearing on it's own and i see no spots on the ground. I was reading that the code being a misfire could have something to do with small pin hole in the cylinder or something causing the loss of coolant
 

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I should also add it seems to come on with initial start up when it is cold and goes away when driving and warmed up. I also notice the coolant resovoir is a little low. Now the coolant isn't just magically disappearing on it's own and i see no spots on the ground. I was reading that the code being a misfire could have something to do with small pin hole in the cylinder or something causing the loss of coolant
I don't believe there's any history of this kind of thing with that 3.6L engine at that low a mileage number (58k), but it almost sounds like you've got a gasket leak with some coolant going into your cylinder(s) after you turn the engine off. Then when you start it up later, the pooled coolant fouls the spark and throws the code. But it burns it out, and everything's fine while the engine's running ... until you stop again, and the cycle repeats. Weird thing is - you'd think you'd be getting a code for a specific cylinder, not the generic P0300 ... but it could still mean there's a leak on two cylinders.

Is it really only happening after the vehicle has sat still for a good amount of time ... like overnight?
 

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Every GM vehicle will display the StabilTrac off warning when the CEL comes on.
Cold misfire that clears up when warmed up could be a leaky injector that leaks down when parked. RB is spot on with cleaner, run it a few times.
Full high end code scan is needed, all 4 code families, to see if a ECT or MAF is running on the edge of it's range for example.
 

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Discussion Starter #6
I don't believe there's any history of this kind of thing with that 3.6L engine at that low a mileage number (58k), but it almost sounds like you've got a gasket leak with some coolant going into your cylinder(s) after you turn the engine off. Then when you start it up later, the pooled coolant fouls the spark and throws the code. But it burns it out, and everything's fine while the engine's running ... until you stop again, and the cycle repeats. Weird thing is - you'd think you'd be getting a code for a specific cylinder, not the generic P0300 ... but it could still mean there's a leak on two cylinders.

Is it really only happening after the vehicle has sat still for a good amount of time ... like overnight?
Yes. Only after it sits. And then once warmed up it is good to go
 

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Discussion Starter #7
Every GM vehicle will display the StabilTrac off warning when the CEL comes on.
Cold misfire that clears up when warmed up could be a leaky injector that leaks down when parked. RB is spot on with cleaner, run it a few times.
Full high end code scan is needed, all 4 code families, to see if a ECT or MAF is running on the edge of it's range for example.
I will definitely try a bottle of cleaner
 
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