Q: Code P300. Tried fixing with no success.

When you receive the OBD code P0300, it means your Buick LeSabre is experiencing a random misfire. This code is given because one or more of the engine’s cylinders are misfiring. While our first instinct is to think spark plugs, typically if the spark plugs were the issue, a more specific code would appear. However we will not rule them out. You mentioned you changed some parts but didn’t specify what was changed on your LeSabre so we cannot say exactly which parts are continuing to cause a problem.

We will look at the most common parts that are changed when misfires occur. These include spark plugs, ignition wires and ignition coils. As your LeSabre is front wheel drive, the engine sits sideways in the engine bay, making the back three spark plugs more difficult to get to. I have both witnessed and been a victim of installing new spark plugs on the back side of the engine and accidentally breaking them by over tightening, due to the difficult angle of getting tools back there.

Along with that, I have also seen brand new aftermarket coils arrive defective, causing the problem you are experiencing with your Buick. However, if those parts are known to be good working parts, it is possible that the ignition control module, which sits underneath the ignition coils, is failing. This is now when I would recommend getting the help of a trusted certified mechanic to diagnose the misfire issue and provide advice on repair.