Manufacturer communication — 2006 GMC YUKON DENALI XL

• Applies to GM passenger cars and trucks, 2002 through 2023, with V6/V8 pushrod engines.

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  GM Passenger Cars and Trucks 2002 2023 All All V6/V8 Pushrod Engines

• Misfire, chirp, squeak, squeal or tick noise, or MIL illuminated.

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  Some customers may comment on one or more of the following conditions: • Misfire • Chirp • Squeak • Squeal • Tick • MIL illuminated

• DTCs P0300 (engine misfire detected) and P0301 through P0308 (misfire detected on cylinders 1 through 8) are listed.

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  P0300: Engine Misfire Detected • P0301: Cylinder 1 Misfire Detected • P0302: Cylinder 2 Misfire Detected • P0303: Cylinder 3 Misfire Detected • P0304: Cylinder 4 Misfire Detected • P0305: Cylinder 5 Misfire Detected • P0306: Cylinder 6 Misfire Detected • P0307: Cylinder 7 Misfire Detected • P0308: Cylinder 8 Misfire Detected

Possible causes

• Possible causes: 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. A verified noise is not eliminated by canceling 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).

2. If applying pressure to 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. Disconnect the coils and injectors on one bank, run the engine with that valve cover removed, back off the rocker arm a couple of turns and listen for a change in the noise.

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   2. Disconnect the coils and injectors on one bank of the engine, run the engine with the related valve cover removed, and back off the related rocker arm a couple of turns and listen for a change in the noise.

4. Measure cam lobe lift at the pushrod side of the rocker arm and compare with other rockers on the same bank; the misfiring or ticking cylinder should have clearly less lift.

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   3. 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. The misfiring/ticking cylinder should obviously have less lift than the comparison cylinders if this is the result of a worn lifter roller and/or cam lobe.

5. A good indicator of a sticking valve is misfires that keep counting 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. 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, and the plastic lifter guide for the affected lifter.

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  Notice: 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 (For 2010 Model Year, replace all the plastic lifter guides).

Caution

• A damaged cam lobe is easy to overlook through the lifter bores, and unworn lifter rollers do not mean the cam lobes are okay; inspect both carefully.

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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. Both pieces need to be carefully inspected.