System Too Lean error codes

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Mar 25, 2007 | 12:38 PM

Truck Issues

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System Too Lean error codes

Hi,

My '98 Ford Explorer indicates 171 & 174 error codes, Bank 1 and Bank 2 System Too Lean. Is this caused from a bad upstream or downstream sensor?
Can you tell me where both downstream and upstream sensors are located (ie. driver side, between the manifold and the converter) I have 4 and am not sure which to replace? Is System Too Lean related to lack of Air or Fuel?
Will the errors cause the truck to keep stalling when I come to a full stop?

Thanks,
Patrick

Mar 25, 2007 | 12:48 PM

Beast12

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Joined: Mar 2003

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From: Sarnia, Ontario, CANADA!

Thread moved to the Explorer forum.

-Matt

Mar 26, 2007 | 11:21 AM

aquanaut20

Cargo Master

Joined: Aug 2003

Posts: 3,263

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From: BC Canada

these codes indicating lean on both bank usualy mean that you have a leak at the intake manifold, Look for broken, loose vacuam hoses and test for leaky gaskets.

Mar 26, 2007 | 08:15 PM

Truck Issues

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Thank you for the reply! I'm sorry for the incorrect forum as I've looked for Explorer Forum without success.

Thanks...

Mar 26, 2007 | 10:08 PM

MazdaRangerGuy

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Joined: Jul 2005

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This code is almost NEVER caused by a defective O2 sensor, and when it is, there are usually other codes present.

Your lean codes are almost always caused by a vacuum leak, or a dirty Mass Air Flow sensor. Check the basics... vacuum lines, hoses... PCV valve... spray some carb cleaner around the intake area while the vehicle is running and listen for an idle change.. if it changes then you just sprayed where the leak is!

If nothing comes up, remove your MAF and clean the elements using brake cleaner or intake cleaner spray.

If that doesn't fix it then replace your intake gaskets.

Good luck