2015 Tahoe - P0171 Lean Bank 1 and Rough Idle

Question

My dash just lit up with a check engine light and the truck feels like it is stumbling whenever I am stopped at a red light. I checked it with a basic scanner and got P0171, but the Bank 2 seems to be hovering just below the threshold. It feels like it has a vacuum leak but I cannot hear any whistling under the hood.

Jake Morrison · Accepted Answer

Found it was the PCV Foul Air Tube (Part #12639648) had a hairline crack at the quick-connect fitting near the back of the manifold. It was sucking air only when the engine shifted slightly under load or low vacuum. Replaced the tube for about $25 and cleared the codes; fuel trims returned to +/- 3% immediately and the idle is smooth as glass now.

Luis Hernandez · Answer

You should check your Short Term Fuel Trims at idle versus 2500 RPM. If the trims improve at higher RPM, you definitely have a vacuum leak. Check the intake manifold gaskets as these are known to shrink over time on the EcoTec3 engines.

Brian O'Connor · Answer

Take a look at the PCV hose that runs from the driver side valve cover to the intake. They get brittle and crack right at the fitting. Also, spray some brake cleaner around the base of the intake manifold while it is idling to see if the engine RPM changes.

Jordan Lee · Answer

It could be a failing high-pressure fuel pump (HPFP) causing a lean condition, although that usually triggers a P00C6 code. Since you have P0101 too, make sure your air filter housing is snapped shut completely; air bypassing the sensor will cause this.

2015 Tahoe - P0171 Lean Bank 1 and Rough Idle

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