P0303 DTC code
Well cylinder misfire codes can be difficult to diagnose since there are many factors that contribute to the misfire condition. Here is a good overview of the P0303 DTC code from
obd-codes.com :
P0303 Code - Cylinder #3 Misfire
Technical Description
Cylinder #3 Misfire Detected
What does that mean?
A P0303 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
Symptoms may include:
- the engine may be harder to start
- the engine may stumble / stumble, and/or hesitate
- other symptoms may also be present
Causes
A code P0303 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.
btw: I remember something about corroded injector connectors being a problem on GM vehicles. The recommended fix was to clean the connections and apply dielectric grease to prevent corrosion.