O2 Oxygen Sensor Upstream Downstream for Ford Focus (2008-2011) 2.0L

Direct-Fit Upstream & Downstream Oxygen Sensor Kit for 2008-2011 Ford Focus (C170)

What it Does: This matched upstream and downstream oxygen sensor kit monitors exhaust oxygen on the 2008-2011 Ford Focus (C170) 2.0L Duratec 20 for precise PCM fuel control.

The Stock Ford Focus Oxygen Sensor Failure

Over extended mileage, factory oxygen sensors on the C170 Focus with the 2.0L Duratec 20 suffer thermal fatigue, silicon poisoning, and carbon fouling. Degraded internal heater circuits delay sensor warm-up and distort millivolt switching signals sent to the PCM. Once upstream response slows or downstream accuracy drops, closed-loop fuel trims drift and trigger fault codes such as P0135, P0141, or P0171.

Common Symptoms of a Failing OEM Oxygen Sensor

• Check Engine Light: Triggers P0135 (upstream heater), P0141 (downstream heater), or P0420 codes.
• Rough Idle: Lazy voltage switching causes rich/lean oscillation and throttle hesitation.
• Poor Fuel Economy: Open-loop enrichment wastes fuel and fails emissions readiness.

The Direct-Fit Zirconia Oxygen Sensor Solution

Replacing both sensors as a matched pair restores crisp closed-loop fueling and catalyst monitoring on the C170 chassis. Built to match OEM numbers 234-4107 (upstream) and 234-4370 (downstream), each unit pairs a zirconia ceramic element with a corrosion-resistant stainless steel housing. Factory-length leads and weatherproof connectors plug directly into the 2.0L Duratec 20 harness without splicing.

What's Included

• 1 Upstream Oxygen Sensor (234-4107)
• 1 Downstream Oxygen Sensor (234-4370)

Technical Specifications

Compatibility

• 2008-2011 Ford Focus 2.0L (Upstream & Downstream Positions)

Frequently Asked Questions & Fitment Warnings

Does this fit the C170 Focus?

Yes. Fits 2008-2011 Ford Focus models with the 2.0L Duratec 20 engine. Confirm your 2.0L engine and 2008-2011 model year before ordering; 2006-2007 models are excluded.

Will this clear P0135 or P0141 fault codes?

Yes, when caused by worn sensors or open heaters. Installing 234-4107 and 234-4370 restores proper heater resistance and switching response after resetting the PCM.

Is splicing or special hardware required for installation?

No splicing is required. Both units use OEM-style connectors for plug-and-play installation; torque to factory spec with an O2 sensor socket.

The Ford Precision Standard

Restoring accurate exhaust feedback keeps your C170 Focus emissions-ready with consistent fuel economy. Built to factory electrical and thread specifications, this matched pair ensures reliable operation.