Check engine light on and code P0420

Hi,

The converter is the likely cause. The sensor could have an issue, but I suspect it's acting that way because of the converter. If the sensor was an issue, I feel you would have gotten a different code.

I have to be honest, anytime I've seen a P0420, it was the converter. I can't guarantee it, but that is what I'm thinking.

Here are directions for the replacement specific to your vehicle. The pics below correlate with the directions.

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2002 Buick Park Avenue V6-3.8L VIN K
Exhaust Manifold Pipe Replacement
Vehicle Engine, Cooling and Exhaust Exhaust System Exhaust Pipe Service and Repair Removal and Replacement Exhaust Manifold Pipe Replacement
EXHAUST MANIFOLD PIPE REPLACEMENT
Exhaust Manifold Pipe Replacement

Removal Procedure

Caution: Refer to Exhaust Service Caution in Service Precautions.

Caution: Refer to Protective Goggles and Gloves Caution in Service Precautions.

Pic 1

1. Raise and support the vehicle.
2. Remove the four nuts securing the catalytic converter to the exhaust manifold pipe.

Notice: Refer to Flex Decoupler Notice in Service Precautions.

3. Position the exhaust system rearward, enough to allow the studs located in the front of the catalytic converter to clear the exhaust manifold pipe.
4. Remove the catalytic converter gasket. Do not reuse the gasket.

Pic 2

5. Remove the two nuts attaching the exhaust manifold pipe to the right exhaust manifold.
6. Remove the exhaust manifold pipe and the gasket. Do not reuse the gasket.

Installation Procedure

Notice: Refer to Exhaust System Inspection Notice in Service Precautions.

Pic 3

1. Place a NEW exhaust manifold pipe gasket over the right exhaust manifold studs.
2. Position the exhaust manifold pipe to the right exhaust manifold.

Notice: Refer to Fastener Notice in Service Precautions.

3. Install the two nuts attaching the exhaust manifold pipe to the right exhaust manifold.
Tighten the exhaust manifold pipe nuts to 40 Nm (30 ft. Lbs.).

Pic 4

4. Place a NEW catalytic converter gasket over the catalytic converter studs.

Notice: Refer to Flex Decoupler Notice in Service Precautions.

5. Position the catalytic converter to the exhaust manifold pipe.
6. Install the four nuts in order to secure the catalytic converter to the exhaust manifold pipe.
Tighten the catalytic converter nuts to 25 Nm (18 ft. Lbs.).
7. Lower the vehicle.

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I hope this helps. Let me know if you have other questions.

Take care and God Bless,

Joe

Is that the only code present?

Joe

The 171 sets when the PCM identifies the vehicle is running lean. The PCM then compensates by adding fuel to the air/fuel mixture. If that happened for an extended time due to a faulty injector or O2 sensor, it could have caused a converter issue. Was anything done to repair that issue?

Joe