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Discussion Starter #1
Hey Guys,
My 2003 Duratec (SEL) is pulling code P0136. Is this the upstream or downstream O2 sensor from the converter? I know that the upstream sensor can control (thru the PCM) the air/ fuel mixture, but does the downstream sensor have any effect other than data collection?

In an earlier thread, someone mentioned possibility of a loose or shorted connection at the steering wheel or under the seat. Are there connectors for the sensors in those locations?

My wife drives it more than I do, she complains intermittently about an odor that smells like burning rubber. Anybody know what's up with that?

I'm a Design Engineer, which makes me a shade tree mechanic, but I do like to take care of as much of the maintenance that I can.

Recent stuff:
New Plugs (Autolite DPlat), Wires, Coil pack.
Cleaned throttle body (thoroughly) and MAF sensor.
New Rotors/ pads

Bought car new, 70k now and still runs like a bat out of hell. I'b buy another in a heartbeat.

Thanks for any light you can shed on the sensor problem.


Premium Member
10,022 Posts
PO136 - Bank 1 downstream HO2S Sensor Circuit Malfunction


The post-cat (downstream) sensors ONLY monitor catalytic converter efficiency. They do not affect A/F ratio at all.

If the odor smells like rotten eggs, it's Sulfur and is a sign of bad cats.

EDIT: For clarification, bank 1 is the rear bank by the firewall.
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