Installation Procedure

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If the catalytic converter was replaced, perform the following:
1. 1.1. Apply anti-seize compound
  GM P/N 12377953 or equivalent to the threads of the old oxygen sensors.
2. 1.2. Install the oxygen sensors.
  NOTE: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
  
  Tighten
  
  Tighten the sensors to 42 N.m (31 lb ft).
Install a NEW exhaust seal to the exhaust manifold.
Install the catalytic converter.
Slide the catalytic converter hanger into the exhaust pipe hanger bracket.

Fig 2: Installing Catalytic Converter

Courtesy of GENERAL MOTORS CORP.

Install the left exhaust manifold pipe nuts.
Tighten

Tighten the nuts to 50 N.m (39 lb ft).

Fig 3: Installing Left Exhaust Manifold Pipe Nuts

Courtesy of GENERAL MOTORS CORP.

Connect the oxygen sensor electrical connectors (1, 2).

Fig 4: Installing Oxygen Sensor Electrical Connectors

Courtesy of GENERAL MOTORS CORP.

Connect the CPA retainers.
Install the muffler. Refer to MUFFLER REPLACEMENT (4.8L AND 5.3L ENGINES) or MUFFLER REPLACEMENT (6.0L AND 8.1L ENGINES) .
Lower the vehicle.