2005 Chev Aveo - Code P0300

[MarionB2BAuto]

Well gentlemen (and ladies if you are reading) I implore again on your knowledge. I am fighting a loosing battle it appears. I have a customer with a 2005 Chevy Aveo with a P0300, and history missfires on cylinders 1 and 4. Their complaint is CEL light on and flashing, and "hold" light on, vehicle will not shift into 4th gear. Initial testing and inspection was that the plugs and wires appear to be ok, ohm testing out within spec. Fuel appears to be normal and fuel trim is ok. Test drive vehicle and engine performs wonderfully, but will set CEL and will flash when over 45MPH steady cruise or accelerate, however missfire counts show zero, or intermittently may pop 1 or two. I have never seen this before where there was no physical signs or data signs of a missfire, but the computer says there is. To be on the safe side, we did replace the coil pack at the customers request, and have relearned crankshaft variation. Fuel is not an issue as far as we can tell. Anyone have an idea? I am almost inclined to believe the computer has gone mental.

[ricmorin]

Did you see TSB 05-06-01-030D? It references misfires and PO300 with valve sealing problems. May be worth a look.

[steven kiser]

Again going way way out here but this may be the end result of improper oil. We purchase a lot of parts from a local G.M. dealer and they had a run of denied warranty claims on these engines because of a local lube shack not using the correct oil.

[MarionB2BAuto]

I will look at the TSB, thank you.

Steven, any explanation on WHY the incorrect oil causes this problem?

[Tim Martin]

If I may jump in. The issue with the incorrect weight of oil is that the tolerances in these engines is so close that lubrication needs to be very thin to get through fast enough. Valve guide tolerances, camshaft bearing tolerances, oil pump tolerances, and the list goes on. I know some shops around here only have one weight of oil they use and we do work after them some. That particular engine calls for 5w-30w oil. I too have seen where the incorrect oil can cause misfires. Worth looking into.

hth

[liljoe]

Incorrect oil weight also affects the variable cam timing actuators on cars with variable cam timing........ Seen bunches of fords with vct codes fixed by changing oil to correct weight......

[MarionB2BAuto]

Thanks. all valid thoughts. I may just change the engine oil myself to confirm. Question still stands, why would there be a code set, but it not show up on either of the tech2 missfire lists?

[steven kiser]

Sorry for the lapse in posting here. The V V T will mess up #'s 1 & 4 but only at high speeds. The flashing code means the cat is being damaged and the mis fire is triggered because there is no way the PCM can determine the mis fire is a timing issue. The PCM expects to see a change is the air fuel readings because of a pre set program and if it doesn't see it will throw a code. If the timing is retarded it will throw a rich reading and if the PCM is programmed to see a certain % and it's richer than it should it will think rich because of misfire. I'm confusing myself here but if the oil is incorrect the valve timing will be off. One thing i would do here is keep customer in the loop because if it is an improper oil there may be other unseen damage and you don't want to own this when something else crashes. These engines will fail catastrophically because of incorrect oil.

[Tim Martin]

For the record, the 1.6L engine in an 05 Aveo does not have a variable cam timing sprocket on either of the camshafts.

That being said, I can thoroughly agree with the issue of wrong weight oil on a variable camshaft timing sprocket.