Check Engine Light and PO135

[Scorpion8]

My 98 Contour 2.0 Zetec has the check engine light on. I was able to get the code scanned and it'd PO135 - Oxygen Sensor Heater Circuit Bank 1 Side 1. What's bank 1 side 1 of an inline 4 cylinder engine? A web search doesn't tell me much, so do I replace the oxygen sensor or something else? My Haynes manual is rather vague about a sensor heater circuit. Okay, not vague, but non-existent. There are two sensors, correct? One in the exhaust mainfold and one by the cat. I would think this would point to the exhaust manifold sensor. Any help?

 

[beyondloadedSE]

There is only 1 bank on a 4 cylinder engine because its an inline motor.

On a V6, bank 1 is in the rear, bank 2 is the front.

Upstream is before the cat (first O2 sensor if starting from the head and working your way down the exhaust manifold). Downstream is after the cat. Replace your O2 sensor and you should be good to go.

 

[Tony2005]

.. Replace your Upper O2 sensor and you should be good to go.

The upper O2 sensor is the one closest to the the engine for the Zetec (before the catalytic converter). That is the one you want to replace.

 

[amc49]

Yup, change the upper one. Heater just heats sensor up to operating temp faster. It's internal inside sensor. Earlier sensors had no heaters, Ford found out that PCM could go to closed loop quicker and thus lower emissions by adding it. Light off temp of sensor around 600 degrees, takes too long for exhaust heat of cold engine alone to get there.

 

[Scorpion8]

Thanks all! Got a bead on one to pick up tomorrow. Also going to get my own OBD-II reader so I can t-shoot these things on my own. Thankee-much!