Customers may complain about a ticking noise, engine misfire and/or SES light. This may be the result of an AFM (Active Fuel Management for displacement-on-demand) lifter that unlocks as soon as the engine is started or one that is mechanically collapsed/stuck.
This TSB applies to the following vehicles:
* 2008-2009 Buick LaCrosse, Allure (Canada only)
* 2007-2009 Cadillac Escalade
* 2007-2009 Chevrolet Avalanche
* 2007-2009 Chevrolet Silverado, Suburban, Tahoe
* 2006-2009 Chevrolet Trailblazer
* 2006-2009 Chevrolet Impala SS
* 2006-2007 Chevrolet Monte Carlo SS
* 2006-2009 GMC Envoy
* 2007-2009 GMC Sierra, Yukon
* 2005-2008 Pontiac Grand Prix GXP
* 2006-2009 Saab 97x
(with a V8 engine and AFM (RPO Codes L76, LC9, LFA, LH6, LMG, LS4 and LYS)
If an AFM lifter unlocks as soon as the engine is started, a SES light and DTC P0300 will be experienced with engine misfires on cylinder 1, 4, 6 or 7 but it is unlikely that any noise will be experienced. If an AFM lifter is mechanically collapsed/stuck, a consistent valvetrain tick noise, SES light and DTC P0300 will be experienced with engine misfires on cylinder 1, 4, 6 or 7.
If this concern is experienced, perform SI diagnosis. If SI does not isolate the cause of this concern, perform the following tests:
* Cylinder deactivation (Active Fuel Management) system compression test in SI. If the running compression of the misfiring cylinder stays below 25 psi regardless of the AFM solenoid being commanded on or off, the AFM lifter is mechanically collapsed/stuck or unlocking as soon as the engine is started.
* Cylinder deactivation (AFM) valve lifter oil manifold diagnosis and testing in SI. If the test above isolated a possible AFM lifter concern, it will lead to this test, which tests the VLOM (Valve Lifter Oil Manifold) for proper operation. SI states a limited amount of air will leak from the bleed holes and outlet ports even when solenoids are off, and compare the amount of leakage to verify all 4 solenoids are operating the same. If it isolates a concern with the VLOM, replace it and re-evaluate the concern.
* If the tests above isolate an AFM concern, or if no rocker/valve movement is noted with the valve cover removed, follow SI repair procedures to replace the pair of lifters for the related cylinder. Before installing the new lifters, blow out the related lifter control oil passages with the old lifters removed. Also, inspect the VLOM oil filter under the pressure sending unit for debris/sludge and clean or replace as necessary.
* NOTE: Please follow the diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
Important: Inspect the original AFM lifters before returning them for warranty. If an AFM lifter is collapsed, damaged or has a locking pin that is partially disengaged, follow the steps below to return it to brand quality, along with a copy of the repair order, an oil sample and the related questionnaire from Step 3 below.
1. Place the affected lifter in a plastic bag and label the location it came from.
2. Remove the oil filter, disable the anti-drainback valve with a screwdriver or awl and drain the oil from the filter into a CLEAN GLASS bottle. A clean and dry Snapple iced tea bottle works very well for this. Please do not clean the bottle with any solvents, as we will be looking for PPM in the oil sample.
3. Fill out this questionnaire:
Miles on oil (since last oil change):__________
Brand of oil (if known): ______________
Viscosity rating of oil if known:___________
Can all previous oil changes be documented? Y/N
Note the mileage at which all previous oil changes took place__________
4. Return the suspect lifter, oil sample, a copy of the repair order and completed questionnaire from Step 3 to:
Jay Dankovich
GM Service Operations
Mail Code 480-204-015
30501 Van Dyke Ave.
Warren, MI 48090
