Stabilitrack and traction control lights

[wsteele]

@tights24

P0300 is a Random Misfire... not a hard/dedicated misfire.

That alone will cause the Stabilitrac and Traction Control lights to come on... which scares a lot of people into thinking there is more wrong/going on then there actually is.

P0455 is a Gross Leak on the EVAP system which is really no big deal as far as running is concerned.

I would start off simple.

When is the last time the spark plugs and wires were changed???

I would have to disagree.

A P0300 is Random/Multiple misfire. An occasional misfire in random cylinders may or may not light up the Stabilitrack/TC errors, but a hard misfire in two cylinders will produce a P0300 and the ST/TC error. Actually a single cylinder hard misfire will also produce that ST/TC condition (kind of sorry I know that).

His mechanic has stated they tested the compression and he had two cylinders at zero compression and one very low. It would be nice if they had done a little more research on that front, but a P0300 and two cylinders not firing at all, certainly fits all the data provided so far.

He may have bad plugs and wires (and they very well could be responsible for the misfires) but again, given his explaination of how the symptoms manifested themselves as well as the compression test results, he probably should get to the bottom of the obvious stuff before starting to change plugs and wires.

At least, that is the way I see it.

 

[tights24]

@tights24

P0300 is a Random Misfire... not a hard/dedicated misfire.

That alone will cause the Stabilitrac and Traction Control lights to come on... which scares a lot of people into thinking there is more wrong/going on then there actually is.

P0455 is a Gross Leak on the EVAP system which is really no big deal as far as running is concerned.

I would start off simple.

When is the last time the spark plugs and wires were changed???

This was certainly not a matter of it not running. I could barely drive it. When it was dropped off at the garage, it wouldn't run for them at all. So they started their digging and eventually found no compression on 2 cylinders and a third that was super low. He thinks it's the lifters(?) and the cam, but can't be sure there's not something else wrong until he digs into it. I suppose the risk is to have them dig into it and get so far into replacing parts with labor and parts cost that it would have been cheaper to just get a reman with a warranty and call it a day...

 

[CaptainAmerica1]

Sounds like your afm lifters took a dump do an afm delete $2500ish if you have to pay someone to do it. Drive it till the rings or bearings die…
The mechanic can pull the valve covers and verify. If that’s not it, your rings are toast. I’d buy a used low mileage LMF ($1800ish plus R&R)and tune the afm out.

 

[kbuskill]

I would have to disagree.

A P0300 is Random/Multiple misfire. An occasional misfire in random cylinders may or may not light up the Stabilitrack/TC errors, but a hard misfire in two cylinders will produce a P0300 and the ST/TC error. Actually a single cylinder hard misfire will also produce that ST/TC condition (kind of sorry I know that).

His mechanic has stated they tested the compression and he had two cylinders at zero compression and one very low. It would be nice if they had done a little more research on that front, but a P0300 and two cylinders not firing at all, certainly fits all the data provided so far.

He may have bad plugs and wires (and they very well could be responsible for the misfires) but again, given his explaination of how the symptoms manifested themselves as well as the compression test results, he probably should get to the bottom of the obvious stuff before starting to change plugs and wires.

At least, that is the way I see it.

I get what your saying and would normally agree BUT...

If you have two completely dead cylinders, with zero compression, why wouldn't you have two codes for hard misfires on those two cylinders instead of random misfires?

I'm not saying the shop was lying but it takes longer to run a compression check on all eight cylinders than it does to pull both valve covers and watch the rockers to see if they are all moving. Seems like if they were already that far in wouldn't that be the next logical step in order to give the customer a definitive answer?

I can literally have my drivers side valve cover off in 2 minutes. Pull the 5 bolts that hold the coil pack brackets and lay them off to the side and pull the 4 bolts in the valve cover and your in.

I guess I am just naturally skeptical of mechanics shops. I have seen way to many people taken advantage of because they didn't know any better.

With 206k miles on this engine, with the way some of these LS engines like to drink oil, if it hasn't had the plugs changed in a long time they could definitely be fouling out and causing random misfires.

Any way, it was just a suggestion, if you like it try it, if not throw it away... lol

 

[wsteele]

I get what your saying and would normally agree BUT...

If you have two completely dead cylinders, with zero compression, why wouldn't you have two codes for hard misfires on those two cylinders instead of random misfires?

I'm not saying the shop was lying but it takes longer to run a compression check on all eight cylinders than it does to pull both valve covers and watch the rockers to see if they are all moving. Seems like if they were already that far in wouldn't that be the next logical step in order to give the customer a definitive answer?

I can literally have my drivers side valve cover off in 2 minutes. Pull the 5 bolts that hold the coil pack brackets and lay them off to the side and pull the 4 bolts in the valve cover and your in.

I guess I am just naturally skeptical of mechanics shops. I have seen way to many people taken advantage of because they didn't know any better.

I don’t know the criteria GM uses for when they throw a P0300 versus a P030x, code when multiple cylinders are misfiring, perhaps he has enough other less frequent cylinder misses that the ECU can’t decide, IDK, but I know it happens (the P0300 versus multiple P030x codes). It would be pretty helpful to see the cylinder misfire count history with their scan tool.

I don’t disagree with the skepticism, frankly the diagnosis seems a little sparse, especially when a decision between a reman and open ended major mechanical work are the stated options. I have never worked in a shop, but I have done a lot of compression/leak down tests and if I found a few cylinders with zero compression, I would likely want to at least attempt to isolate the problem to the top or bottom end before “tearing into it”.

On the other hand, maybe the techs did that and didn’t feel compelled to go into detail. No compression in one or more cylinders definitely points to something ominous if it is real, I think I would want a little more detail before making an expensive decision.

To the OP, even if you trust these guys implicitly, perhaps you could ask for a little more detail on the testing they did to isolate the zero compression issue (there can be more than one root cause to zero compression). Also, tear down doesn’t take a lot of labor to get to the point of being able to see pretty far into things. You certainly don’t have to rack up “rebuild hours” to get a pretty good idea what you are looking at damage wise.

 

[wjburken]

I would think a collapsed lifter would not lead to no compression, most likely as they usually fail in the “short” configuration and won’t open the valves. I’m thinking it’s a broken spring. Had it happen on our 2007 Denali at about 140K. Ran like it was an old Johnny Popper. Got lucky that it didn’t take out a piston.

Did the shop pull the valve cover and look at anything or just pull a plug and check compression?

 

[kbuskill]

I would think a collapsed lifter would not lead to no compression, most likely as they usually fail in the “short” configuration and won’t open the valves. I’m thinking it’s a broken spring. Had it happen on our 2007 Denali at about 140K. Ran like it was an old Johnny Popper. Got lucky that it didn’t take out a piston.

Did the shop pull the valve cover and look at anything or just pull a plug and check compression?

This would definitely make sense as he was driving it when all of a sudden he had the issue. If the lifters collapsed you would think he would have mentioned the awful tapping/clattering sound that would have likely accompanied it.

 

[tights24]

This would definitely make sense as he was driving it when all of a sudden he had the issue. If the lifters collapsed you would think he would have mentioned the awful tapping/clattering sound that would have likely accompanied it.

Thank you all for the replies/suggestions. To try to answer some of them:

1. They went into detail about which cylinder but frankly I forgot.
2. I was doing roughly 75mph when this happened on the highway. First thing was a noticeable semi-loss of power and slight shuddering. I honestly thought it was a tire going down as it was a very quick rapping as if I was down on the valve stem at that speed. I started to slow down and the light popped up. As luck would have it I tried to get to the first exit, just a half mile away, and of course cars were lined up back onto the highway. I got into line and it started running super rough. I pulled off, put it into neutral and it leveled off fine. Decided to put it back into drive, put on the 4 ways, and drive through the grass to a good spot down off the exit to park it.
3. They still have not called to tell me pricing, but they are going to give me pricing to open things up and potentially fix what they think it may be, and also pricing for a reman. I also asked them for pricing for a once over to address any other major expenses that may come up.

 

[wsteele]

I would think a collapsed lifter would not lead to no compression, most likely as they usually fail in the “short” configuration and won’t open the valves. I’m thinking it’s a broken spring. Had it happen on our 2007 Denali at about 140K. Ran like it was an old Johnny Popper. Got lucky that it didn’t take out a piston.

Did the shop pull the valve cover and look at anything or just pull a plug and check compression?

I had the same thing on my Yukon, but I think broken valve springs on more than one cylinder at the same time might be a low probability. And then there is the "low compression" on the third cylinder.

 

[tights24]

Which means what exactly? Some kind of ghost issue?

And then there is the "low compression" on the third cylinder.