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PO171 and PO174 Diagnostic Guide for 2007 Chevrolet Silverado with Stock Engine

Model: 2007 Silverado Fault Code: P0171 Posted: 2010-08-04 10:30

Hi everyone, I'm new to this forum and wanted to ask for some help regarding a check engine light issue on my 2007 WT-style Chevrolet Silverado. The truck has approximately 33,000 miles and remains stock with no modifications. The check engine light came on recently, and the OBD2 scan tool revealed two fault codes: PO171 (System Too Lean Bank 1) and PO174 (System Too Lean Bank 2). This indicates a lean air-fuel mixture in both engine banks. I've already cleaned the Mass Air Flow (MAF) sensor and inspected the intake manifold for leaks, but no visible issues were found. The symptoms include: - Significant fuel mileage drop - Loss of engine power under load - Engine stumbles or dies when idling after startup - Harsh shifting from 1st to 2nd gear around 15 mph I'm looking for reliable troubleshooting steps and possible root causes. Any advice would be greatly appreciated! Thanks in advance!

Related fault codes
P0171P0174
Comments (4)
Anonymous 2010-08-04 11:31

Try idling your truck and spraying a small amount of brake cleaner directly onto the intake manifold. If the idle speed drops noticeably, this could indicate an intake gasket leak. Also, inspect the fuel system pressure to rule out a clogged fuel filter or dirty injectors/fuel pump.

Anonymous 2010-08-04 11:33

The pcv valve system might have something to do with it also check for an improper seating oil dipstick because it is part of the pcv system.If you have a scanner check the fuel trim.

Anonymous 2010-08-04 12:26

Just a quick follow-up: how do I properly test the fuel system pressure? Is there a standard procedure or tool required?

Anonymous 2010-08-05 06:39

You'll need to purchase, borrow, or rent a fuel pressure gauge. Connect it to the Schrader valve located on the fuel rail, just downstream of the fuel regulator, to measure system pressure accurately.