Service Engine Soon (SES) Light On, Reduced Vehicle Power/Acceleration/Speed, Diagnostic Trouble Code (DTC) P0420 (Diagnosis and Replace Catalytic Converter)

Some customers may comment of the SES light on and/or possible reduced vehicle power, acceleration and reduced top speed. DTC P0420 may be set.

The catalytic converter efficiency may be too low and/or restricted.

Follow the service procedure below for catalytic converter diagnosis and replacement .

1. For diagnostic information, refer to DTC P0420 SI Document ID #792317
2. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle SI Document ID #377101.

Caution: 

•	In order to avoid being burned, do not service the exhaust system while it is still hot. Service the system when it is cool.

•	Always wear protective goggles and gloves when removing exhaust parts as falling rust and sharp edges from worn exhaust components could result in serious personal injury.

3. Support the exhaust system near the resonator with a suitable adjustable jack.



4. Remove the 4 nuts securing the catalytic converter to the rear exhaust manifold pipe.



5. Remove the 2 bolts securing the center exhaust hangers to the rear suspension support brackets.
6. Remove the catalytic converter from the rear exhaust manifold pipe.
7. Remove the catalytic converter gasket and discard the gasket.

Important: Use care not to overextend the heated oxygen sensor pigtail.

8. Lower the exhaust system with the adjustable jack to allow clearance for the cut-off tool.




Important: Ensure the cut is made on the catalytic converter side of the pipe.

9. Cut (2) the catalytic converter (3) from the resonator inlet pipe (1) ahead of the step but as close to the step as the tool will permit.
10. Remove and properly discard the catalytic converter.

Important: 

1. DO NOT REPLACE the following complete exhaust systems when replacing the catalytic converter.

•

25727006

•

88959335

•

88959334

•

25727009

•

25709529

2. Ensure the catalytic converter heat shield is upward. The "honeycomb" side faces downward.
11. Slide the new catalytic converter, P/N 25755681, onto the resonator inlet pipe until it is fully seated against the heated oxygen sensor boss.
12. Install a new exhaust seal, P/N 03544534, on the four studs.
13. Install the converter onto the rear exhaust manifold pipe.
14. Install the four nuts securing the catalytic converter to the rear exhaust manifold pipe.
15. Install the 2 bolts securing the center exhaust hangers to the rear suspension support brackets.

Tighten

1. Tighten the catalytic converter nuts in a crisscross pattern to 25 Nm (18 lb ft).
2. Tighten the center exhaust hanger bolts to 30 Nm (22 lb ft).

Important: Ensure the catalytic converter outlet pipe is fully seated against the heated oxygen sensor boss.

16. Install two exhaust clamps, P/N 15992529, on the converter pipe with the two clamp ends 180 degrees from each other. Each set of clamp nuts should face opposite directions for proper sealing.

Tighten
Tighten the service clamp nuts to 30 N·m(22 lb ft),

17. Remove the adjustable jack stand.
18. Lower the vehicle and inspect for exhaust leaks.

Parts are currently available from GMSPO.

For vehicles repaired under warranty, use: