OBD-II Trouble Code Description for P0303 GMC

Cylinder 3 Misfire Detected

What does this mean?

OBD2 Code P0303 GM definition:
A P0303 GM code means that the the car’s computer has detected that one of the engine’s cylinders is not firing properly. In this case it’s cylinder #3.

Symptoms

Possible sumptoms of OBD code P0303 GM
the engine may be harder to start the engine may stumble / stumble, and/or hesitate other symptoms may also be present

Causes

Possible causes of OBD code P0303 GM
A code P0303 GM may mean that one or more of the following has happened: Faulty spark plug or wire Faulty coil (pack) Faulty oxygen sensor(s) Faulty fuel injector Burned exhaust valve Faulty catalytic converter(s) Running out of fuel Poor compression Defective computer

Possible Solutions

If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back. 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.