Testing an O2 sensor???
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Mountain Pass
Joined: Dec 2003
Posts: 154
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Testing an O2 sensor???
Hi, I have an 88 302 F-150 and would like to know if anyone knows how to test an o2 sensor? I have a test procedure here but seems a bit confusing to me. I have 12v to the sensor lead and a good ground. The procedure says to probe the other lead with the engine warm to see if I can get a volt reading of 0.45 + or - and for it to change rapidly. Well mine reads 0.18 and it only changes from 0.18 to 0.19 and up and down. I can rev the engine up and down and only get a slight voltage drop or raise but it is consistent at 0.18 to 0.19 or so. How much should I get? I have also disconnected vacuum and same results. Any suggestions? Is it fried or what? Any help appreciated. Thanks in advance.
Posting Guru
Joined: Feb 2007
Posts: 1,006
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Even though it does not make a difference in how it runs, the Check Engine Light will come on when it is unplugged.
As far as being hard of fuel, how long has it been since the plugs, wires, cap, and rotor were changed. This is the first place I go when mileage is crappy and there are no Check Engine Light problems.
As far as being hard of fuel, how long has it been since the plugs, wires, cap, and rotor were changed. This is the first place I go when mileage is crappy and there are no Check Engine Light problems.
Elder User
Joined: Feb 2008
Posts: 797
Likes: 1
From: ohio
USUALLY,at least what i have learned with my ford truck is that if the o2 sensor doesnt read what its supposed to the check engine light will either flicker after ten min of driving or will just stay on. I tried testing it but when i just went out and bought a new one all problems were solved. But i had code 41
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
On a motor that's running right with all sensors in range, the O2 sensor only switches when the A/F ratio is at 14.7:1. The problem with testing it in your truck is that if the rich condition is not being caused by a bad O2 sensor, if it's something else that's not under computer control like a stuck or leaking fuel pressure regulator, then the motor will always be rich because the computer doesn't have enough fuel trim adjustment, and the O2 sensor won't switch like it's supposed to. These narrowband O2 sensors switch back and forth between 0 and 1 volt.. which in practice is often more like 0.3v to 0.7v with 0.45v equal to 14.7:1.
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