2013 Chevy Silverado P0171 and P0174 Lean Both Banks

Question

My truck is idling very rough and the check engine light just started flashing when I stopped at a red light. It feels like it wants to stall out when I am idling, but it runs mostly fine once I get up to highway speeds. I hooked up my scanner and I am seeing lean codes for both banks.

turbo_tony · Accepted Answer

It turned out to be the intake manifold gaskets and a cracked PCV hose at the back of the driver side valve cover. I replaced the gaskets with the updated Fel-Pro MS97219 set and swapped the PCV line. Total cost for parts was about $55 and it took me 2 hours in the driveway. Fuel trims are back to +/- 3% now and the idle is rock solid.

Rachel Nguyen · Answer

Check your long-term fuel trims at idle versus 2500 RPM. If the trims improve significantly at higher RPMs, you definitely have a vacuum leak somewhere behind the throttle body.

Sarah Thompson · Answer

Common issue on these NNBS trucks is the intake manifold gaskets. They are made of orange silicone and flatten out over time, especially in cold weather, causing a massive air leak.

torque_terry · Answer

Spray some brake cleaner or use a smoke machine around the intake runners while the engine is running. If the idle smooths out or the fuel trims drop, you found your leak point.

2013 Chevy Silverado P0171 and P0174 Lean Both Banks

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