O2 heater circuit malfunction
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New User
Joined: May 2003
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From: S.W. Florida
O2 heater circuit malfunction
Hello.
I own a '95 Ranger "Splash" 4.0, 5-speed. The check engine light is on. The OBD II is showing all three of my O2 sensors expieriencing "O2 Heater Circuit Malfunctions". I changed out the sensors which didn't make any difference in the codes re-appearing. Anyone want to take a shot at this?
Sincerely, Sundog
I own a '95 Ranger "Splash" 4.0, 5-speed. The check engine light is on. The OBD II is showing all three of my O2 sensors expieriencing "O2 Heater Circuit Malfunctions". I changed out the sensors which didn't make any difference in the codes re-appearing. Anyone want to take a shot at this?
Sincerely, Sundog
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Sundog, my Haynes manual says the O2 sensors get battery voltage (about 10v) that operates the heaters. This voltage goes through a relay, but the book dosen't say where it is. I would suspect the relay is in the box that's under the hood on the driver's side. It sounds like the relay may be the culprit, since all of the sensors show a heater circuit trouble.....
Thread Starter
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New User
Joined: May 2003
Posts: 4
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From: S.W. Florida
Success!!
HALLEILULIA!! 
Well Alright! You were close enough to get me on the right track in resolving this problem. Replacing a blown 15 amp. fuse solved this mystery. It was in fact located in the engine compartment fuse/relay box. The Ford owners manual labels the fuse as "power point". My Hayes manual labels it as the "power train control module oxygen sensor system" (#4). OF COURSE!! I replaced the fuse, cleared the codes and I'm good.
The fuse apparently had blown when the wiring harness for the after CAT O2 sensor had dropped onto the drive shaft, wore through and grounded out. I'd found and fixed that while replacing the sensors but never considered that it may have blown a fuse somewhere. Very cool. I'm stoked!
Finially, I can drive without that annoying little CEL light staring at me.Take that,idiot light!
Well Alright! You were close enough to get me on the right track in resolving this problem. Replacing a blown 15 amp. fuse solved this mystery. It was in fact located in the engine compartment fuse/relay box. The Ford owners manual labels the fuse as "power point". My Hayes manual labels it as the "power train control module oxygen sensor system" (#4). OF COURSE!! I replaced the fuse, cleared the codes and I'm good. The fuse apparently had blown when the wiring harness for the after CAT O2 sensor had dropped onto the drive shaft, wore through and grounded out. I'd found and fixed that while replacing the sensors but never considered that it may have blown a fuse somewhere. Very cool. I'm stoked!
Finially, I can drive without that annoying little CEL light staring at me.Take that,idiot light!
Last edited by sundog2000; Jan 27, 2004 at 08:40 PM.
