How to Fix Error P2270 (Lambda Sensor) on a Citroen C3

Error P2270 indicates a malfunction of the downstream lambda sensor (the one after the catalyst), but the real issue may be the upstream sensor (the one that regulates the air-fuel mixture). If the car hesitates, has an irregular idle, and loses power when hot, the culprit is almost always the upstream sensor sending incorrect data to the ECU. Using a diagnostic tool (e.g., Texa), read the parameters of the sensors.

If the upstream sensor is in closed loop, the ECU is adjusting the mixture based on its data. If that data is incorrect, the engine runs poorly.

Quick test: Disconnect the upstream sensor. If the engine runs better, the problem is the sensor.

The engine will enter open loop and use a default mapping, but this is not a permanent solution. Replace the upstream lambda sensor.

The new sensor has 5 wires (the downstream one has 4). Also check the catalyst: if it is white, the mixture was lean; if it is black, it was rich. The ideal colour is brownish.

Replacement is straightforward: unscrew the sensor, insert the new one, and reconnect the connector. After replacement, the engine will run smoothly and the mixture will be correct.

If you have changed spark plugs and coils without resolving the issue, the problem was indeed the sensor.