Oxygen Sensor – Before Catalyst – Smart Forfour Fortwo – 2014-on – 226934803R

This direct-fit oxygen sensor (lambda probe / oxygen probe) restores correct air-fuel mixture, fuel economy and emissions performance on the Smart Forfour Fortwo (2014 onwards). Built to OEM specification and matching part numbers 0258027031, 226934803R, H8201140217, 8201140217 and A4535420500. Also fits equivalent Dacia and Renault models.

Common signs of failure

A failing lambda or oxygen sensor will turn on the check engine light and commonly log fault codes in the P0130–P0167 range (sensor circuit and heater faults). Drivers typically notice a sudden drop in fuel economy, rough or fluctuating idle, hesitation under load, a sulphur or rotten-egg smell from the exhaust, and in many cases an MOT emissions failure. On modern diesels and direct-injection petrols, a stuck or slow-responding sensor can also push the engine into limp mode.

Fitment notes

Plug-and-play installation with the correct factory connector — no diagnostic coding required. Most engines run a pre-cat (upstream) and a post-cat (downstream) sensor; cross-check your existing part number and the position on the exhaust to make sure you're ordering the right one. Apply a smear of anti-seize compound on the threads before fitting and torque to manufacturer spec. Standard 5 wire connector. Position: Front, In Front Of The Catalyst.

Frequently asked questions

How do I know if my lambda sensor is faulty?

An OBD2 scan showing P0130-series codes plus poor fuel economy is the clearest sign. Live data showing the sensor stuck at a flat voltage (instead of oscillating between roughly 0.1V and 0.9V) confirms a faulty sensor.

Pre-cat or post-cat — which one do I need?

Pre-cat sensors (upstream of the catalytic converter) control the fuel mixture. Post-cat sensors (downstream) monitor catalyst efficiency. Match the OEM number on your old sensor to the numbers listed above to be sure.

Will a new sensor fix my fuel economy?

If the original sensor is biased lean or rich, a correct replacement typically restores MPG within a tank or two of fuel. Drive at least 20-30 miles after fitting to allow the ECU to re-learn.