Manufacturer communication — 2006 GMC YUKON DENALI XL

• Applies to 1999-2013 GMC Savana, Sierra and Yukon (with a V8 engine per the model list) (note: the Yukon years run later than the years this service covers).

  the passage

  1999-2013 GMC Savana, Sierra, Yukon

• With the SES light on, a P0300-P0308 DTC is found with misfires counting on a single cylinder, which may or may not be felt.

  the passage

  If the SES light is on, the technician will find a P0300-P0308 DTC with misfires counting on a single cylinder that may or may not be felt.

• The noise may be described as a chirp, squeak, squeal or tick and may increase off of idle.

  the passage

  The noise may be described as a chirp, squeak, squeal, or tick noise and may increase off of idle.

Possible causes

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

  the passage

  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.

Steps to confirm (in the document’s order)

1. Press on the rocker arms with a wooden hammer handle while the noise is present; if pressing the valve side of a rocker changes the noise, a lifter and/or cam lobe concern on that cylinder is most likely.

   the passage

   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.

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

   the passage

   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.

3. A bore scope or pen light may help when inspecting the cam lobes through the lifter bores.

   the passage

   It may help to use a bore scope or pen light when inspecting the cam lobes through the lifter bores.

4. A good sign of a sticking valve is that misfires keep counting during an aggressive deceleration with engine braking.

   the passage

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

5. The Cylinder Leakage Test in SI should typically isolate valve leakage by showing excessive leakage past an intake or exhaust valve compared with the others.

   the passage

   Typically, the Cylinder Leakage Test outlined in SI should isolate valve leakage by finding excessive leakage past an intake or exhaust valve, as compared with others.

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

   the passage

   Sometimes, the two broken pieces of the spring will remain stacked together so it may be 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

1. If a worn cam lobe or lifter roller is found, replace the camshaft and all lifters per SI, plus the plastic lifter guide for the affected lifter (for the 2010 model year, all the plastic lifter guides).

   the passage

   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 of the plastic lifter guides).

2. If force is needed to tap the valve off its seat, there is excessive carbon build up, which may be repaired by decarboning the engine.

   the passage

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