I keep getting code P0300 on my 2002 Chrysler Concorde LX with 115,000 miles. I've replaced the spark plugs, plug boots/spring conductors and all four O2 snsors (due to prior codes). Any ideas on what I should try next.
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Check that the wiring harness to the coils is getting 12v, this will confirm if the pcm is sending a signal for the sparks to fire. Check the ignition coil is sending spark to the plugs with a spark plug tester.
this obd2 trouble code table can help you understand the meaning of code. for this code, you can try,
If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
i know this us703 is useful for your car.
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.
Thank you for all the information. I don't see how you made it worse unless the injectors were not installed correctly. If you remove them you are suppose to replace the o-ring on each of them and oil them (the o-rings) before installing them. I would check the air filter and the CAT (for excessive back pressure. Also check the rest of the exhaust for damage. If a pipe is kinked or flattened it would need repair. Also GM's are known for some issues with there e-vap systems. You may want to check it out. The gas cap, charcoal canister, vacuum lines. Well good luck.
If the plugs get wet, then you have a spark problem somewhere in the ignition system. Pull a spark plug and hold it against a ground while you turn the engine over. You need to see a fat blue spark. If not, check the distributor, spark plug wires and coils. An easy way to test for spark is with an inexpensive spark tester. This is a device that is readily available at most auto supply stores. If the plugs do not fire properly, check the spark plug wires for fraying or cracking. Next, you need to check the coil(s). If firing voltage is low (weak spark), measure the coil primary and secondary resistance with an ohmmeter. If it is out of specifications, replace the coil. Also, make sure the coil is receiving normal voltage from the PCM or ignition module. If it is low, check the charging system for anything that may be reducing alternator output (battery and alternator cable connections, ground connections and voltage output).
If it ran good prior to spark plug replacement, then yes, I'd be looking real close at the plug wire to that particular spark plug. Perhaps it pulled apart inside boot upon removal. It may even be an indication that they are all getting weak, and time to think about a new set if it's originals.