1. Raise and suitably support the vehicle. Refer to Lifting and Jacking the Vehicle.
2. Remove the nuts securing the catalytic converter to the left exhaust manifold.
3. Lower the vehicle.
4. Remove the spark plugs. Refer to Spark Plug Replacement for the 5.3L engine or Spark Plug Replacement for the 6.0L engine.



5. Remove the heat shield bolts, and shield from the exhaust manifold.
6. Remove the exhaust manifold bolts, manifold, and gasket.
7. Discard the gasket.
8. Clean and inspect the exhaust manifold. Refer to Exhaust Manifold Cleaning and Inspection for the 5.3L engine or Exhaust Manifold Cleaning and Inspection for the 6.0L engine.

Important: 

Notice: Refer to Fastener Notice in the Preface section.





Important: Do not apply sealant to the first 3 threads of the bolt.

1. Apply a 5 mm (0.2 in) wide band of threadlock GM P/N 12345493, (Canadian P/N 10953488), or equivalent to the threads of the exhaust manifold bolts.
2. Install the exhaust manifold NEW gasket and bolts.

Tighten

1. Tighten the bolts a first pass to 15 N·m (11 lb ft). Tighten the bolts beginning with the center 2 bolts. Alternate from side-to-side, and work toward the outside bolts.
2. Tighten the bolts a final pass to 25 N·m (18 lb ft). Tighten the bolts beginning with the center 2 bolts. Alternate from side-to-side, and work toward the outside bolts.
3. Install the heat shield, and bolts to the exhaust manifold.

Tighten
Tighten the bolts to 9 N·m (80 lb in).

4. Using a flat punch, bend over the exposed edge of the exhaust manifold gasket at the rear of the left cylinder head.
5. Install the spark plugs. Refer to Spark Plug Replacement for the 5.3L engine or Spark Plug Replacement for the 6.0L engine.
6. Raise the vehicle.



7. Install the nuts that secure the catalytic converter to the left exhaust manifold.

Tighten
Tighten the nuts to 50 N·m (37 lb ft).

8. Lower the vehicle.