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Vacuum leak

I had this exact thing happen on my 98 Expedition Eddie Bauer. After changing all 4 of my o2 sensors the check engine light came back on. So I performed a complete tuneup while performing the tuneup I fould the vacuum line had been pulled from the PCV valve. I believe the shop my wife took it to last pulled it off for a repeat visit. I made sure both ends of the vacuum line were connected well after changing the PCV valve. I removed the codes and drove a couple hundred miles without the check engine light coming back on. In short, you probably have a vacuum leak or are needing to tune the engine. Both are easily accomplished.

I concur. Had the exact same problem with my 98 Expedition Eddie Bauer. Thankfully, I have an honest mechanic. Vacuum line was the culprit. Diagnostic codes indicated that all four O2 sensors needed replacing. Once 12 dollar part replaced, all codes cleared up and truck has run like a charm since.


scanned codes don't necessarily give you the answer to the problem, just lead you to the answer. When the o2 sensor code came up, the sensor(s) should be then checked, not just replaced. Also I would think the probability of all 4 o2 sensors going bad at the same time would be approaching zero.

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โˆ™ 2009-11-25 00:43:58
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Q: What could cause the check engine light error code for o2 sensors to come back on with same code after all 4 sensors were replaced in my expedition?
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