Catalytic Converter Replacement 4.3L, 4.8L, and 5.3L Engines

1. Raise and suitably support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
2. If equipped, unclip the oxygen sensor connection from the floor reinforcement.
3. Disconnect the oxygen sensor electrical connector.



4. Remove the oxygen sensor clips from the frame.
5. Disconnect the connector position assurance (CPA) retainers.
6. Disconnect the oxygen sensor electrical connectors.



7. Unclip the oxygen sensors electrical connectors from the following:

•

Hose clip

•	Transmission crossmember

8. Disconnect the CPA retainers.
9. Disconnect the oxygen sensor electrical connectors (1, 2).



10. Remove the left exhaust manifold pipe nuts.



11. Remove the right exhaust manifold pipe nuts.



12. Remove the exhaust muffler nuts.
13. Remove the catalytic converter.



14. If necessary, remove the oxygen sensors.

Notice: 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.

1. If necessary, install the oxygen sensors.

1.1.	Apply anti-seize compound GM P/N 12377953 or equivalent to the threads of the old oxygen sensors.

1.2.	Install the oxygen sensors.

Tighten
Tighten the oxygen sensors to 42 N·m (31 lb ft).

2. Install the catalytic convertor.



3. Install NEW exhaust manifold pipe seals to the exhaust manifolds.
4. Install the right exhaust manifold pipe nuts until sung.



5. Install the left exhaust manifold pipe nuts until snug.
6. Tighten the exhaust manifold pipe nuts.

Tighten
Tighten the exhaust manifold pipe nuts to 50 N·m (39 lb ft).




7. Install the exhaust muffler nuts.

Tighten
Tighten the exhaust muffler nuts to 40 N·m (30 lb ft).




8. Connect the oxygen sensor electrical connectors (1, 2).
9. Connect the CPA retainers.
10. Clip the oxygen sensors electrical connectors to the following:

•

Hose clip

•	Transmission crossmember




11. Connect the oxygen sensor electrical connectors.
12. Connect the CPA retainers.
13. Install the clip around the engine harness and the oxygen sensor pigtail.



14. Connect the oxygen sensor electrical connector.
15. If equipped, clip the oxygen sensor connection to the floor reinforcement.
16. Lower the vehicle.

Catalytic Converter Replacement 6.0L and 8.1L Engines

1. Depending on which side is being replaced, perform one of the following steps:

•	Remove the exhaust muffler nuts.

•

or

•	Loosen the exhaust pipe clamp.

2. Remove the necessary exhaust system hangers so that the pipes can be separated.
3. Use a jack stand to support the exhaust.



4. Remove the transmission support. Refer to Transmission Support Replacement in Frame and Underbody.
5. Disconnect the connector position assurance (CPA) retainers.
6. Disconnect the oxygen sensor electrical connectors (1, 2).



7. Remove the clip around the engine harness and oxygen sensor pigtail.
8. Disconnect the CPA retainer.
9. Disconnect the oxygen sensor electrical connector.
10. Remove the exhaust pipe hanger bracket bolts.
11. Remove the nuts attaching the insulator to the bracket.
12. Remove the insulator from the bracket.



13. Remove the right exhaust manifold pipe nuts.
14. Remove the left exhaust manifold pipe nuts.



15. Remove the left catalytic converter.



16. If equipped with a 6.0L engine, with regular production option (RPO) Y91, remove the left catalytic converter.



17. If equipped with a 6.0L engine, with RPO Y91, remove the right catalytic converter.



18. Remove the oxygen sensors if the catalytic converter(s) are to be replaced.

Notice: Refer to Fastener Notice in the Preface section.

1. If the catalytic converter was replaced, perform the following:

1.1.	Apply anti-seize compound GM P/N 12377953 or equivalent to the threads of the old oxygen sensors.

1.2.	Install the oxygen sensors.

Tighten
Tighten the sensor to 42 N·m (31 lb ft).




2. If equipped with a 6.0L engine, with RPO Y91, install a NEW exhaust manifold pipe seal to the right catalytic converter.
3. Install the right catalytic converter .



4. If equipped with a 6.0L engine, with RPO Y91, install a NEW exhaust seal to the left catalytic converter.
5. Install the catalytic converter.



6. Install a NEW exhaust seal to the catalytic converter.
7. Install the catalytic converter.



8. Install the left exhaust manifold pipe nuts.
9. Tighten the right exhaust manifold pipe nuts.

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




10. Install the insulator to the bracket.
11. Install the nuts attaching the insulator to the bracket.

Tighten
Tighten the nuts to 40 N·m (30 lb ft).

12. Install the exhaust pipe hanger bracket bolts.

Tighten
Tighten the bolts to 17 N·m (13 lb ft).

13. Connect the oxygen sensor electrical connector.
14. Connect the CPA retainer.
15. Install the clip around the engine harness and oxygen sensor pigtail.



16. Connect the oxygen sensor electrical connectors (1, 2).
17. Connect the CPA retainers.
18. Install the transmission support. Refer to Transmission Support Replacement in Frame and Underbody.
19. Install the exhaust pipe/catalytic converter to the vehicle.
20. Install the exhaust system hangers.



21. Depending on which side is being replaced, perform one of the following steps:

•	Install the exhaust muffler nuts.

Tighten
Tighten the nuts to 40 N·m (30 lb ft).

•

or

•	Install a NEW exhaust pipe clamp.

Tighten
Tighten the clamp to 44 N·m (33 lb ft).

Catalytic Converter Replacement 6.6L Engine w/California Emissions

1. Raise and suitably support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
2. Support the transmission with a suitable transmission jack.
3. Remove the transmission mount to transmission support nuts.
4. Raise the transmission off of the transmission support.



5. Remove the transmission support crossmember bolts.
6. Remove the transmission support crossmember.



7. If equipped with the 6.6L engine, remove the exhaust muffler nuts.



8. If equipped with a 6.6L engine, loosen the exhaust pipe clamp.
9. Slide the exhaust pipe clamp up onto the exhaust pipe adapter.



10. If equipped with a 6.6L engine, remove the catalytic converter.
11. Slide the catalytic converter hanger out of the exhaust pipe hanger bracket.

1. If equipped with a 6.6L engine, install the catalytic converter.
2. Apply water based lubricant to the exhaust pipe hanger bracket, in order to aid in installation.
3. Slide the catalytic converter hanger into the exhaust pipe hanger bracket.



4. If equipped with the 6.6L engine, install the exhaust muffler nuts until snug.




Important: Ensure that the manifold pipe is square to the exhaust pipe adapter.

5. If equipped with a 6.6L engine, slide the exhaust pipe clamp down and around the pipe connection.

Notice: 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.

6. Tighten the exhaust pipe clamp and muffler nuts.

Tighten

•	Tighten the clamp to 40 N·m (30 lb ft).

•	Tighten the nuts to 40 N·m (30 lb ft).




7. Lower the transmission onto the transmission support.
8. Install the transmission mount to transmission support nuts.

Tighten
Tighten the bolts to 40 N·m (30 lb ft).

9. Remove the support from the transmission.
10. Lower the vehicle.