P0171 System too lean (Bank 1)
Lean codes are incredibly difficult to diagnose. And it’s one trouble code where you don’t want to start throwing parts at the problem. The guys at the parts store will tell you to replace the Oxygen sensor. Nice guess, but probably wrong. They’re assuming that the fuel mixture is correct but the sensor is reporting it wrong. Oxygen sensors DO wear out. But what if the mixture really IS lean? Can it be lean on only one bank (of a V-6 or V-8) engine? You bet. This kind of code screams out for a little diagnostic work. First, check all the vacuum hoses for cracks and correct placement. Next, spray carburetor cleaner around the intake manifold gasket and listen for an increase in engine RPM. Any increase after spraying indicates a vacuum leak.
The Bank 1 indication tells you that the problem is located on the cylinder bank that contains the #1 plug. That varies by make and engine style, so make sure you check the shop manual.
For more information on this repair or any others for your vehicle, buy an online subscription to either Alldatadiy.com or eautorepair.net. Click on this link to compare the two services: Compare Alldata and Eautorepair.
If you just need information for a single repair and want to save money,eautorepair offers a lower price 1-week subscription for only $11.99. Or, if you’ll be working on this vehicle in the future, you can buy a 1-year subscription (Alldatadiy.com for $26.99, or eautorepair.net $29.99)
© 2012 Rick Muscoplat
Alldata and Eautorepair are both professional grade shop manuals. You’ll find more in-depth information and more complete wiring diagrams, along with descriptions of how the systems work. And, you’ll get all that at a price you can afford. Check them out!
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