2015 Silverado 1500 - Rough Idle and P0171 Lean Code Bank 1

Question

My truck is idling really rough and feels like it wants to stall at stoplights. The check engine light just came on and I am getting a P0171 lean bank 1 code. It seems to drive okay at highway speeds, but the idle is driving me crazy.

Jake Morrison · Accepted Answer

The issue was a cracked PCV breather tube (GM Part #12639648) located on the driver side valve cover. The plastic had become brittle and snapped right at the fitting, sucking in a ton of air. I replaced the hose for about $25 and cleared the codes; fuel trims returned to +/- 3% immediately. Make sure to check the O-ring on the new hose as well to ensure a tight seal.

torque_terry · Answer

Have you checked the intake manifold gaskets? Those 5.3L engines are known for the gaskets shrinking over time, which lets extra unmetered air in at idle, though usually that happens more in colder weather.

Sarah Thompson · Answer

Check your fuel trims at idle versus 2500 RPM. If the LTFT (Long Term Fuel Trim) drops significantly when you increase the engine speed, you almost certainly have a vacuum leak after the MAF sensor.

Lina Brooks · Answer

Try spraying some brake cleaner or using a propane torch (unlit) around the PCV hose and intake area while the engine is idling. If the RPMs stumble or jump, you found your leak location.

2015 Silverado 1500 - Rough Idle and P0171 Lean Code Bank 1

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