engines codes

2003 GMC SIERRA
72,000 MILES • V8 • 2WD • AUTOMATIC
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BILLB55
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Codes PO171&PO174. Just replace MAS about a week ago with a reman. Check engine light is on again. Reading the codes above. What should I check next.Changed plugs and wires less than 20,000 miles ago.
Jan 13, 2011 at 10:27 PM
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JACOBANDNICKOLAS
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the codes indicate a lean mixture on both banks of the engine. Check for vacuum leaks first. Check fuel pump pressure. A restricted fuel filter can restrict the fuel supply. Go to our homepage under the DIY section for direction to check fuel pressure. My first guess, however, is a vacuum leak.
Jan 18, 2011 at 9:28 PM