Vehicle: 2000-’03 Buick Park Avenue 3.8L

Symptom: Lack of power, hesitation, surge and/or possible DTC P0420.

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Problem 1 of 3: The catalytic converter has degraded and will need to be replaced.

Test & Fix: DTC P0420 means the rear oxygen (O2) sensor has too much activity. This means it must be working and therefore the catalytic converter is bad and needs to be replaced. Be sure to perform test #3, which addresses a possible cause of the catalytic converter failure.

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Problem 2 of 3: The catalytic converter is plugged.

Test & Fix: Check for back-pressure at the front O2 sensor. If it is more than 1.25 psi at idle or at 2,500 rpm, replace the catalytic converter. Be sure to perform test #3, which addresses a possible cause of the catalytic converter failure.

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Problem 3 of 3: Coolant leakage into the intake manifold causing catalytic converter failure.

Test & Fix: Inspect the intake manifold for signs of coolant. This engine is known for coolant leakage past the intermediate intake manifold gasket and the throttle body gasket. Replace the intermediate intake manifold gasket, the throttle body gasket and the throttle body nuts. Be sure to use medium-duty thread locker. The part number for the gasket kit is 17113137 and the nuts is 11517293.

Courtesy of Identifix, Inc.