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Q: Check Engine Light is on - codes P0313, P0299, P0304

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Around 90k miles had CEL with codes p0313,p0304 car ran poorly and had shop look at it and replaced a coil pack and spark plugs. Around 110k miles CEL returned with p0304 error code returned replaced the other 3 coil packs and new spark plugs. Around 130k miles CEL returned again with error codes p0304 and p0299, I did nothing and reset my CEL. Another 600 miles and CEL returned with error code p0304 I took to shop and they replaced 4 injectors and performed a carbon cleaning. Less than 100 miles CEL returns I do nothing except reset CEL. CEL returns with error code p0313,p0304, and p0299. Where do I start? Do replace the downstream sensor on throttle body? No unusual noises, occasional rough start when cold, not very noticeable

A: Hi there. Based on what you've describe...

Hi there. Based on what you've described, this could be a combination of faults between 2 or more things; however, I don't believe the coils and spark plugs are at fault. One of the codes is set during a low fuel misfire (lean condition), one is specifying a misfire on cylinder 4, and one is a turbo related code; all based on a generic code investigation.

The make and model of the vehicle helps, but is not necessary at the moment. When a low fuel pressure misfire is set, there is a lean condition that has been detected by the sensors and one of the codes is telling us in which cylinder this is occurring. A possibility is a restricted fuel injector, loose injector harness, poor pin fit in the wire harness, and an air leak near that cylinder's port in the intake manifold.

I'm leaning more towards a leak or crack somewhere creating an air leak since we also have a turbo related code stored and an intermittent rough start when cold. I strongly suggest having a qualified technician perform an inspection to determine the root cause. YourMechanic has several available technicians that can assist you with a Check Engine Light inspection and determine exactly what is giving rise to codes P0313, P0299, and P0304.

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