Q: Check Engine Light is on - P0302 and P0304. Ignition coil recently replaced.

asked by on November 15, 2016

My truck has been driving poorly for a couple of days now; a lot of shaking with the check engine and vsc trac lights on. All the spark plugs were changed last year, and I had the ignition coil changed last week but the problem will not go away. The code that I got the very time I ran the diagnostic test was "P0304, and multiple misfires". This coil has been changed and now the code reads "P0302, and multiple misfires", would changing the wires on the coils fix this problem or does all of the coils need to be fixed? If I pay for the ignition coil replacement on the YourMechanic website, will you guys change the coil wires if that's all that needs to be done or will changing all of the coils be necessary? My truck does a lot of shaking regardless if I'm just letting the engine run in the driveway or if I'm trying to drive on the highway. Sometimes i think i smell a little smoke but i could be over exaggerating. Thanks!

My car has 131300 miles.
My car has an automatic transmission.

The two Diagnostic Trouble Codes, P0304 and P0302, refer to cylinder misfiring. A faulty ignition coil, spark plug, wire, and so forth can cause a cylinder to misfire but there are other possible causes, too. Consequently, the only way to determine the actual cause or faulty part is to perform an engine diagnostic during which each relevant part and system is tested.

If an obvious and common cause, such as a bad coil, is not immediately found during the diagnostic, these additional possible causes of engine misfiring would have to be evaluated: oxygen sensor(s), fuel injector, burned exhaust valve, catalytic converter(s), poor compression, clogged EGR valves or tubes, wrong ignition timing, vacuum leaks, low fuel or low fuel pressure, leaking head gasket, bad camshaft or crankshaft sensor, bad mass air flow or throttle position sensor, and defective computer (least likely cause).

I recommend having a certified mechanic, such as one from YourMechanic, come to your location to determine why the car is misfiring and suggest the necessary repairs.

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