Execute a Professional Engine Oil System Flush

1. Purchase a reputable engine oil flush additive compatible with the Subaru Tribeca engine. 2. Add the flush agent to the existing engine oil according to the product's instructions. 3. Idle the engine for the specified duration (usually 10-15 minutes) to allow the additive to break down sludge and deposits throughout the AVCS oil galleries. 4. Immediately drain the oil and replace the oil filter. 5. Refill the engine with fresh, clean oil of the correct viscosity. 6. Use an OBD2 scan tool to clear the stored P0021 code. 7. Monitor the engine's live data for AVCS timing accuracy to confirm the oil pressure is no longer obstructed by internal sludge.

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