Check engine light code P0420

Good morning,

The 420 is a code for the catalytic converter. It needs to be replaced. The internals are worn out and is not processing the gases.

I attached the procedure, pictures and the part for below.

Roy

Catalytic Converter Replacement (LH6/LS2) (5.3L and 6.0L)

Removal Procedure

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1. Remove the heated oxygen sensors (HO2S). Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1, Heated Oxygen Sensor Replacement - Bank 1 Sensor 2, Heated Oxygen Sensor Replacement - Bank 2 Sensor 1, and Heated Oxygen Sensor Replacement - Bank 2 Sensor 2.
2. Remove the rear propeller shaft. Refer to Rear Propeller Shaft Replacement.
3. If equipped with four wheel drive (4WD), remove the front propeller shaft. Refer to Front Propeller Shaft Replacement.
4. Remove the transmission support. Refer to Transmission Support Replacement.
5. Remove the muffler to catalytic converter nuts (1).

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6. Remove the front 2 muffler insulators (3 and 4) from the muffler hangers.
7. Pull back and separate the muffler (2) flange from the catalytic converter flange studs.
8. Reposition and secure the muffler end out of the way.
9. Remove and discard the old exhaust gasket.

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10. Remove the catalytic converter to left exhaust manifold nuts (2).

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11. Remove the catalytic converter to right exhaust manifold nuts (2).

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12. Raise the transmission using the transmission jack for additional catalytic converter pipe clearance.
13. Tilt the catalytic converter in order to lower the left side pipe below the vehicle frame. Rotate the catalytic converter outlet pipe toward the left side of the vehicle to gain the necessary clearance for the right side pipe to clear the vehicle frame. Remove the catalytic converter (1) from the vehicle.
14. Remove and discard the catalytic converter to exhaust manifold seals.

Just to add, Roy is correct that the converter is the normal cause. The o2 sensors are telling the PCM what the oxygen content is in the exhaust.

As long as the engine is running well, there are no other codes and you don't have any exhaust leaks on that side then the converter is the issue. Last thing I would suggest is swapping o2 sensors side to side just to make sure you don't get a P0430 which means you have a sensor issue.

There is no quick fix and the light will come back on.

The only resolution is to replace the converter assembly.

Roy

You are welcome.

We are always glad to help.

Roy