O2 sensors
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Senior User
Joined: Sep 2006
Posts: 107
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O2 sensors
'99 4.0 SOHC Explorer, 110,000 miles
I am thinking of replacing the O2 sensors as part of a complete tuneup. This vehicle has 4 O2 sensors(2 upstream of the cat. convertor and 2 downstream). Do I need to replace all 4 sensors or just the upstream ones? They are kind of pricey!
I am thinking of replacing the O2 sensors as part of a complete tuneup. This vehicle has 4 O2 sensors(2 upstream of the cat. convertor and 2 downstream). Do I need to replace all 4 sensors or just the upstream ones? They are kind of pricey!
Former ******
Joined: Nov 2004
Posts: 4,901
Likes: 2
From: Salt Lake City, Utah
Just replace the upstream sensors. The downstream ones are not prone to contamination, nor are they involved in the fuel management. I wouldn't only replace the rear ones if I was having a problem, but the upstream sensors can have a serious negative impact should they fail, which is why they should be replaced as part of a major tune up.
