Thread: P0420 Code
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Old 07-08-2007, 12:23 PM
goofy123
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Default Steps to Check Problem - P0420

Hi,
I too had the P0420 error code until last week and was trying to find answers as I had no noticeable decrease in performance of my car. Finally I went through a set of steps to isolate the problem, I suggest the following steps:

1. Spray a can of carb cleaner all along the inlet right after the Mass flow sensor to the intake manifold while the car is idling. If you notice any change in idling then you have a intake leak. This will lead to the above code.
2. Check connections of front and rear O2 sensors
3. Check O2 connectivity with ECM (will give details of the ECM points later) - This is a rare case as if there is a loss of connectivity you would also have a O2 sensor code.
4. Sometimes if you have bad plugs or a leaking injector you may also get the code so check if you injectors are leaking by removing them, disconnecting the crank position sensor and turning the ignition to ON position, do not attempt to start the car.
5. Remove rear O2 sensor and start the car if it runs better than before it will mean your CC is plugged up and you need a new CC

Though I would recommend a factory replacement those are very costly you can try to get after market direct fits they run about $150.

Hope this information helps you out. Common problems are with the inlet manifold gasket leakage.
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