P0301 problem

Check engine light on 2000 3.5l reads p0301. I have replaced the ignition coil and spark plugs and reset the codes, but the p0301 returns. Any ideas on what else may be wrong?

Do you feel an actual misfire or roughness and under what conditions?

Yes, at idle there is a definite vibration.

Change the wires. You changed the plugs and coil but you didn't mention changing the wires. The wires often wear out internally and will cause misfires.

Change the wires. You changed the plugs and coil but you didn't mention changing the wires. The wires often wear out internally and will cause misfires.


GTP_Dad! I'm disappointed in you!

He has the 3.5 engine. It doesnt have spark plug wires:grinno:

When you say you replaced the coil, do you mean the cassette that actually has 3 coils in it? Or are you referring to something else?

No matter what is actually wrong we are all guessing here at our desks, this needs on site hands on diagnosis, 100 suggestions accurate or not still may not fix this condition, there are a littany of issues that can cause this.

Life is full of little disappointments. The 3.5 really isn't one of my favorite engines so I don't usually comment on it. If he changed the coils and still has a misfire then either the coil/coils he used are bad or he needs to look to the fuel system such as the injector since that can cause misfires as well.

I changed the 3 coil cassette. I thought I may have gotten a defective one, so I swapped the cassettes for 2-4-6 and 1-3-5 to see if the missfire moved to #6. It did! So tomorrow I will return the part to Advance Auto and wait the 3-4 days for a new one to arrive and try this again. Thanks for your troubleshooting! It's what made me think to try the switch. I'll let you know in a few days if the problem gets resolved.

that's a smart swap. =No wonder why the 3.5L LX5 is my favorite engine.

becareful of the quality of these replacement parts. Sometimes it's better just getting the part from the GM dealership or GMpartsdirect. RockAuto also sells some GM brands.

If you buy from Napa etc: look at the screen and see if there are other choices for a part. =Buy good quality always.

You could probably call the small 'connecting boot' a 'wire' and I suppose it could go bad??