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Code p306 on Jeep Liberty

Hey all
I drive a 2002 Jeep Liberty sport. I started my car yesterday night and things seemed ok but then I noticed my car was shaking more than usual. As I started to drive down the street something didn’t feel right there was a lack of power when accelerating and my car was really laggy as I made the turn I saw the check engine light come on for a few seconds blinking and then it went away. Same lack of power/jerking went on as I was driving and then it went away and my car was fine. Came back home and plugged in code reader. It said code P306. Hoping it’s not an expensive repair. Any ideas on where to start at home? Complements to change first before taking it to the shop?
PS-Car was fine all day yesterday up until night. Was caught off guard by the code.

That code indicates a misfire in cylinder #6. While there can be several possible causes, the most likely one is a bad spark plug in that cylinder. But, since all of the spark plugs are likely the same age, it is probable that you need to replace all of them.

I strongly suggest that you not drive while the CEL is blinking, and that you get it to a competent mechanic a.s.a.p. even if the CEL stays “off”.


P0306 is a misfire code. When the Check Engine light is flashing it is telling you that he car should not be operated or engine and engine systems could suffer damage which could get expensive.

If this vehicle is due or overdue for spark plugs, I’d replace them and the spark plug wires now.

It could be that the problem is environmentally activated, that is by moisture or temperature. If plugs and wires don’t fix it I’d suspect a coil/coil pack, but to be sure, whether before or after trying spark plugs and wires (if due according to mileage schedule) you can take the vehicle to a competent mechanic for diagnosis.

Don’t keep driving it in this condition or you could go from possibly minor problems to something more major.
:palm_tree: :sunglasses: :palm_tree:


Which engine is in this Jeep? Is it a 3.7L?
With a little searching I found that sometimes a P0306 is not an ignition (spark plugs, coils/coil packs) problem, but rather related to intake valves & valve locks, for which there are “revised” parts available for this somewhat common problem.

I think it would behoove you to take the Jeep to a mechanic with experience working on these vehicles and have a proper diagnosis done. The mechanic should be able to explain the chain of events that a diagnosis will follow.
:palm_tree: :sunglasses: :palm_tree:

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Yes it’s a 3.7 liter engine. Was going to replace spark plugs and take it from there otherwise I’ll take it to the shop

Thanks was going to change the spark plugs and take it from there but it was raining yesterday and I hit a couple of big puddles of rain. Either way I’d rather fix the problem sooner rather than later. Will change the plugs and take it from there. I’ll def take it to the shop though

A bit of advice . . .

If a coil and/or plug doesn’t fix it, the mechanic’s very next step should be to perform a compression test on all cylinders

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