Manufacturer communication — 2006 GMC YUKON DENALI XL

• Applies to 2002 through 2018 GM passenger cars and trucks with V6/V8 pushrod engines.

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  Buick GM Passenger Cars and Trucks 2002 2018 All All V6/V8 Pushrod Engines

• A verified noise is not eliminated by cancelling fuel injectors and occurs at camshaft speed (half of crankshaft speed).

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  If a noise is verified, it will not be eliminated by canceling fuel injectors and the noise will occur at camshaft speed (half of crankshaft speed).

• A worn cam lobe generally creates a consistent chirp, squeak, squeal or tick at camshaft speed and/or a misfire with a P0300-P0308 DTC.

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  Generally, a worn cam lobe on this engine family will create a consistent chirp, squeak, squeal or tick noise at camshaft speed and/or a misfire with a P0300-P0308 DTC.

Possible causes

• If SI diagnosis does not isolate it, the cause may be a worn camshaft lobe and/or lifter roller, a sticking valve, valve leakage, a broken valve spring or a collapsed AFM lifter.

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  If SI diagnosis does not isolate the cause of this concern, it may be the result of any of the following: • Worn camshaft lobe and/or lifter roller • A sticking valve • Valve leakage • A broken valve spring • A collapsed AFM (Active Fuel Management) lifter

Steps to confirm (in the document’s order)

1. While the noise is present, press with a wooden hammer handle on the valve side, the push rod side and the side of each rocker arm to find which one is making noise.

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   Use a wooden hammer handle to apply pressure to the following locations of the rocker arms during the noise to determine which one is making noise: • Valve side • Push rod side • Side of the rocker

2. If pressing on the valve side of the rocker changes the noise, a lifter and/or cam lobe concern on that cylinder is most likely.

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   If the noise is changed by applying pressure to the valve side of the rocker, this is most likely the result of a lifter and/or cam lobe concern on that cylinder.

3. Measure cam lobe lift at the push rod side of the rocker arm; it differs from the SI specification but should be similar to the other rockers on the same bank.

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   Measure the cam lobe lift at the push rod side of the rocker arm. The lift in this location will differ from the SI specification but it should be similar as compared with other rockers on the same bank.

4. A damaged cam lobe is easy to overlook through the lifter bores, and unworn lifter rollers do not mean the related cam lobes are okay.

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   It is very easy to overlook a damaged cam lobe when inspecting them through the lifter bores and just because the lifter rollers are not worn, does not mean that the related cam lobes are okay.

5. A good indicator of a sticking valve is misfires that continue to count on an aggressive deceleration with engine braking.

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   A good indicator of a sticking valve is if engine misfires continue to count on an aggressive deceleration with engine braking.

6. With the spring removed, if force is needed to tap the valve off its seat, excessive carbon build up exists, which may be repaired by decarbonizing the engine.

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   If you have to use force to tap the valve off of the seat, excessive carbon build up exists, which may be repaired by decarbonizing the engine.

7. The two pieces of a broken valve spring may stay stacked together and be hard to see; lightly push on different places on the springs with a small hammer handle.

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   Sometimes, the two broken pieces of the spring will remain stacked together making it hard to detect when visually inspecting them. As a result, it may help to lightly push on different places on the springs with a small hammer handle.

Repair

• If a worn camshaft lobe or lifter roller is found, replace the camshaft and all lifters per SI, and also the plastic lifter guide for the lifter that had the damage.

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  Follow SI procedures to replace the camshaft and all lifters if a worn camshaft lobe or lifter roller is found. Also replace the plastic lifter guide for the lifter that had the damaged cam lobe and/or lifter roller