1998 Ford Taurus P0171 P0174 Lean

FORD TAURUS
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ZOGGIN
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I have a 1998 Taurus SE 3.0L V6 DOHC. I recently replaced both upstream O2 sensors and had the OBD codes cleared.

2 days later the check engine light is back on and a scan shows codes 0171 and 0174. Banks 1 and 2 are lean. I also just replaced the fuel filter. I was told that the vacuum line had some cracks it was getting brittle with age.

What is the problem and how is it fixed?
Feb 13, 2007 at 10:36 AM
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GARFIELD
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I hate to say it but a lean condition is not normally caused by the o2 sensors, they normally fail to the rich side not lean. If you have cracked vaccum lines then that is probably your problem. This is the situation, your cars sensors tell the computer how much air is being taken in and schedules the fuel based on that information. Now take a cracked vaccum line will have on that, it is able to ingest air that is not being metered by the sensors so that is why your car is running lean and are getting the codes. I would check all your vaccum lines and replace any that are questionable or excessively hard(don't mistake emission lines for vacuum lines) emission line is hard plastic). Hope it helps.

Gary
Feb 13, 2007 at 11:18 AM

Suggested Repair

Inspect all vacuum lines and replace any that are cracked, brittle, or excessively hard. Unmetered air from a vacuum leak can cause both banks to run lean; do not confuse hard plastic emission lines with vacuum lines.

Conversation Summary

A 1998 Ford Taurus SE 3.0L returned P0171 and P0174 lean codes after both upstream oxygen sensors and the fuel filter were replaced. The expert explained that oxygen sensors more often fail rich, while cracked vacuum lines can admit unmetered air and cause a lean condition. The recommended fix is to inspect all vacuum lines and replace any that are questionable or excessively hard.

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