What is the problem for a Chevy Cobalt with the code P0303.?

Answer 1

0303 Cylinder 3 Misfire Detected Could be a bad plug or plug wire; or an injector problem. Is it running rough? If it sounds smooth, it could be a transient condition. Such as driving on rough roads or lugging the engine, however rough roads/lugging will unlikely set a misfire code with an automatic transmission. I'd give the light several days and see if it goes out. If it's running a bit rough and it's time for plugs and wires anyway you may go ahead and do replace them. Once it's running smoothly, the light will go out soon--three consecutive ignition cycles without a fault. The way it sets a misfire code is the computer checks the crank position sensor every 100 revolutions for any deceleration that a misfire would cause. If it discovers deceleration, it looks at the cam position sensor in order to identify the cylinder. Therefore the PCM may not detect a light misfire right away. If it detects a severe misfire, it will flash the MIL, since a severe misfire could damage the catalytic converter, and disable the lock up torque converter clutch momentarily to rule out the rough road possibility. Since this code is not set by an actual lack of spark, just unexpected engine deceleration, any action that jostles the engine will be read as a misfire.