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

Question

My dash just lit up with a traction control warning and then the check engine light started flashing while idling at a red light. The truck feels like it is gasping for air when I try to merge onto the highway and the idle is very choppy. Plugged in my scanner and I am seeing lean codes for both banks which usually points to a vacuum leak.

Sarah Thompson · Accepted Answer

The issue turned out to be the intake manifold gaskets and a cracked PCV hose at the rear of the driver side valve cover. I replaced the gaskets with a Fel-Pro MS97219 set and swapped the hose. The mounting bolts require a two-pass torque sequence ending at 89 lb-in. Total part cost was about $55 and the fuel trims are now back within +/- 3% at all ranges.

Pete Sanders · Answer

On these EcoTec3 engines, the vacuum pump on the front of the engine or the valve cover PCV system are common leak points. Also, take a close look at the corrugated plastic intake tube for cracks that open up when the engine torques over.

Megan Rivera · Answer

Check your Long Term Fuel Trims (LTFT) at idle versus 2500 RPM. If the trims improve at higher RPMs, you definitely have a vacuum leak. If they get worse, you are looking at a fuel delivery issue like a weak high-pressure pump or clogged injectors.

fleet_chief_42 · Answer

Don't rule out the MAF sensor. If it's dirty or reporting lower than 5-7 g/s at idle for a V8, it will cause the ECU to under-calculate the fuel requirement. Try cleaning it with dedicated MAF cleaner spray first.

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

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