2015 Tahoe P0171 and P0174 Lean Both Banks - Hesitation on Accel

Question

My dash just lit up with a check engine light and the truck feels like it is falling on its face when I pull away from a stoplight. I have a rough idle when sitting in drive and it feels like it might stall, but it clears up once I get up to highway speeds. I checked with a basic scanner and I am getting lean codes for both banks.

Jordan Lee · Accepted Answer

The issue was a leaking intake manifold gasket. I performed a smoke test and found heavy smoke billowing out from the passenger side rear intake runner. I replaced the gaskets with a new AC Delco set (Part #12626354) and torqued the bolts to 89 lb-in in the proper sequence. The fuel trims returned to +/- 3% immediately and the hesitation is completely gone. Total cost for parts was about $45 and took two hours of work.

Lina Brooks · Answer

Check your long term fuel trims (LTFT) at idle and then at 2500 RPM. If the trims improve significantly at higher RPMs, you definitely have a vacuum leak somewhere behind the MAF sensor.

Tom Patel · Answer

On these EcoTec3 engines, look at the PCV tube that runs from the valve cover to the intake manifold. They are made of brittle plastic and often crack at the quick-connect fittings, causing an unmetered air leak.

garagegrease · Answer

Don't overlook a failing high-pressure fuel pump (HPFP) or a clogged fuel filter mesh in the tank. If your fuel pressure is dropping below 40 PSI on the low side, it will trigger lean codes on both banks simultaneously.

2015 Tahoe P0171 and P0174 Lean Both Banks - Hesitation on Accel

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