Multiple Displacement system must use correct 5W-20 oil on Jeep Grand Cherokee

Problem Description and Possible Solution
Vehicles equipped with the multiple displacement system (MDS) must use the correct 5W-20 oil in order to function properly.
Problem Data
RepairPal Verified
Average mileage: 90,000 (90,000–90,000)
Engines affected: 5.7L V8, 5.7L V8 HEMI
6 model years affected: 2005, 2006, 2007, 2008, more2009, 2010
8 people reported this problem
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05w 30 oil fully synthetic can be used but anything heavier will bring on the P01521 DTC code - now using 05w 30 with no problems