Contour Enthusiasts Group Archives Forums General Troubleshooting HO2S heater circuit malfunction

I posted in "Maintenance" by mistake...
I have the following codes: P0135, P0141, P0155, and P0161. The only forum (discussion) I located expained that these codes are related to a "HO2S heater circuit malfunction." This is where the confusion begins... can anyone give me advise on what to check/replace??
I have a 1997 Contour GL - V6 - Manual Trans (90,000 miles). I changed the upstream O2 sensor against the firewall yesterday, and the codes came back shortly after running the car. I also have the other three O2 sensors that are going to be changed shortly. I did notice alot of cracked wiring in the engine harness, and am following up on the recall I found on this site regarding the engine wiring. I would appreciate any assistance with this.

Welcome. Your codes are for all four of the O2 sensors. There is a very good chance it is the wiring harness as you mentioned. Do send it in to Ford to check the wiring harness. 10 years/100k miles extended customer satisfaction warranty.

This site (found with a Google search) may be of some help:

http://autorepair.about.com/cs/troubleshooting/l/bl_obd_main.htm

These codes are only concerned with the upstream sensors so there is no need to even consider changing the downstream sensors. The downstream sensors only have to do with cat effeciency.

It is uncommon for both upstream oxygen sensors to act up at the same time. One of those codes was for high voltage which would be an indication that it is reading a rich mixture. I suppose it's possible that the radiator side sensor is malfunctioning and causing the engine to run rich causing the high voltage reading on the firewall side, but that is just speculation. I would be more suspecious that for some reason the engine isn't running well and that the oxygen sensor readings just reflect that without necessarily being defective.

Good luck with your research, and perhaps someone that has experienced those codes can chime in.

I must have crossed my eyes or something when I was looking those codes up. Now I don't see anything about high voltage and I can see that the codes are for all four sensors. Sorry about that.

This would be a very unusual circumstance that could make all four act up. I suspect either a wiring or PCM issue.

Doesn't anyone else have any wisdom to share?

I appreciate the info you provided.. the thought process makes perfect sense to me.. I was told by another enthusiast that my problem is with one of the upstream O2 sensors, and if the heater circuit fails, it will trigger a false indicator of all 4 sensors like I am getting now.. any thoughts on that?? I have already changed the upstream bank 1 sensor, and I have the remaining 3 sensors ordered... to expensive an Autozone. Any additional insight on this issue would be appreciated.

I finally recieved the O2 sensors in the mail, and have replaced both upstream, and both downstream sensors. I made repairs to the upstream bank 1 sensor harness, as it was falling apart just past the connector. I also found fuse #13 in the underhood fuse box blown. I found out it controls the O2 sensor heater circuit, and if my understanding is correct, when the PCM looked for the O2 sensor readings, and did nto find it, it was generating my eng light??? I suspect because of the harness condition. The check engine light and all 4 codes have left me for the time being, meanwhile my car is on it's way to Ford for the harness recall. Thanks for the input. This is an awesome site!!!