GMC Yukon 2000–2006

From the manufacturer’s document

• Applies to：Applies to GMC Yukon models, 2002 - 2018, with a V8 engine.
• Condition：An SES light may come on on low mileage vehicles or vehicles that recently had the catalytic converter replaced, with DTCs P0420 and/or P0430 stored.
• Cause：On a new vehicle, catalytic converter efficiency DTCs P0420 and P0430 are disabled for the first hour of engine run time to allow break-in of the catalytic converter.
• Confirm：On a new/low mileage vehicle with these DTCs, use the Tech 2 to verify engine run time on the Engine Hour Meter in the IPC Data Display/Data 1 List.
• Cause：If the engine run time is less than one hour, the battery may have been disconnected, or another vehicle power loss event may have occurred, during vehicle manufacturing.
• Cause：If the DTCs set shortly after the catalytic converter is replaced, it may be because the engine run time restrictions are no longer in place since the vehicle is no longer new.
• Cause：As a result, the catalytic converter may not have completed a thorough break-in cycle after replacement, possibly resulting in a false DTC P0420 and/or P0430.
• Repair：Clear the DTCs and perform the drive cycle given in the document.
• Repair：Drive cycle step: drive the vehicle at sustained highway speed for 25 to 30 minutes.
• Repair：Drive cycle step: restart the engine and resume highway speed for an additional 10 to 15 minutes.
• Confirm：Finally, restart the engine and operate the vehicle at the conditions for running the DTC P0420/430 tests, and make sure the vehicle passes them.
• Repair：If the diagnostics do not pass, perform SI diagnostics and repair as necessary.

From the manufacturer’s document

• Applies to：Applies to Buick, Cadillac, Chevrolet and GMC passenger cars and trucks, model years 2000 to 2022, gasoline engines only.
• Condition：Customers may comment that the MIL is illuminated.
• Condition：Initial diagnosis may show fuel trim and O2 sensor related codes including P0101, P0137, P0138, P0140, P0141, P0157, P0158, P0160 and P0161.
• Condition：The listed codes also include P0171, P0174, P0420, P0430, P1174 and P1175.
• Confirm：If normal SI diagnostics do not lead to a resolution and an intake vacuum leak or exhaust leak is suspected, use the GE-52250 Variable Pressure Leak Detector (preferred), the J-41416 ultrasonic leak tester, or possibly soapy water with low pressure air into the tailpipe to find the leak.
• Caution：All of these tests are much more effective if the throttle body is covered or sealed.
• Confirm：For an intake leak, introduce the smoke into the brake booster hose or the oil dipstick tube; soapy water can be sprayed near the gasket, seams and all vacuum nipples.
• Confirm：For an exhaust leak, put the hose with smoke or air into the tailpipe sealed with shop towels, then spray soapy water around seals, seams and bosses.
• Cause：These methods find small leaks around the O2 sensor embossments and slight cracks in an intake plenum or gasket.
• Parts：No parts are required for this repair.

From the manufacturer’s document

• Applies to：Applies to all 2000 - 2019 models with gasoline engines.
• Condition：The SES light is on, and initial diagnosis may show fuel trim and/or O2 sensor related codes such as P0171, P0174, P0420 and P0430.
• Confirm：If normal SI diagnostics do not resolve it and an intake vacuum leak or exhaust leak is suspected, the J41413-200 Evaporative System Tester smoke machine, the J-41416 ultrasonic leak tester, or soapy water with low pressure air into the tailpipe may help find the leak.
• Caution：All of these tests are much more effective if the throttle body is covered/sealed.
• Confirm：For an intake leak, the smoke can be introduced into the brake booster hose or the oil dipstick tube.
• Confirm：Soapy water can be sprayed near the gasket and seams and on all vacuum nipples.
• Confirm：For an exhaust leak, a hose into the tailpipe carrying smoke or air, sealed with shop towels, is effective.
• Confirm：Then spray soapy water around the seals, seams and bosses.
• Confirm：These methods are very good for finding small leaks around the O2 sensor bosses and slight cracks in an intake plenum or gasket.

From the manufacturer’s document

• Applies to：Applies to 2015 and prior GM cars and gasoline-powered light duty and HD trucks.
• Condition：The catalytic converter has come apart or has set P0420 and/or P0430.
• Confirm：If the converter has failed with no apparent reason, inspect for a poor crimp at the circuit terminal on the engine bank with the concern.
• Confirm：The grounds in question are those for the ignition system, fuel injector or the ECM.
• Confirm：Inspect the ground for corrosion or damage at the ground terminal ring, fasteners and grounding surfaces.
• Repair：If no corrosion or damage is found, tighten the ground bolt to the proper torque.