High-quality replacement Lambda Sensor (Oxygen Sensor) designed for 1.0i Citroën C1 and Peugeot 107 applications. This upstream (pre-catalyst) sensor with a 4‑pin connector restores accurate exhaust oxygen measurement for proper engine fueling and emissions control. Ideal for professional workshops and experienced DIY mechanics who need a reliable OE-fit part (1618Q5) to clear rich/lean running symptoms, improve fuel economy and reduce emissions.

Technical Information

• Manufacturer: Stellantis / Citroën / Peugeot
• Model: Citroën C1 (1.0i), Peugeot 107 (1.0i)
• Product Codes: 1618Q5
• Other Numbers: —

Function

The Lambda (Oxygen) Sensor monitors the oxygen content in the exhaust gases upstream of the catalytic converter and sends a voltage signal to the engine control unit (ECU). The ECU uses this signal to adjust air–fuel ratio for efficient combustion. A 4‑pin sensor indicates an integrated heater circuit plus signal/ground connections, allowing the sensor to reach operating temperature quickly and deliver accurate readings shortly after engine start.

How Replacement Is Performed

Replacement is straightforward for a trained technician or competent DIY mechanic with the right tools:

• Work on a cooled exhaust system and safely raise the vehicle to access the exhaust manifold/downpipe area.
• Disconnect the sensor electrical connector and inspect wiring for damage or corrosion.
• Remove the old sensor using an oxygen sensor socket or appropriate wrench. Apply penetrating lubricant if the sensor is seized, allowing time to soak.
• Compare the new sensor to the old unit to confirm connector and thread compatibility.
• If the new sensor is not pre-coated, apply a small amount of anti‑seize to the threads (avoid getting anti‑seize on the sensor tip or heater terminals).
• Install and tighten the sensor to the manufacturer’s specified torque, reconnect the electrical connector and lower the vehicle.
• Clear any stored fault codes and perform a test drive to allow the ECU to adapt to the new sensor signal.

Installation Recommendations

• Always work with the engine cold to avoid burns. Use proper jack stands or a lift—never rely on a jack alone.
• Use an oxygen sensor socket or appropriate tool to prevent damage to the sensor hex and wiring.
• Inspect and secure the wiring harness and connector to prevent chafing or contact with hot components.
• Avoid excessive force when disconnecting or connecting the electrical plug; check pins for corrosion and secure fit.
• If fault codes persist after replacement, review wiring and grounds; perform a live data check to confirm the sensor switches correctly between rich and lean conditions.

Why This Part Most Commonly Fails

• Contamination From Oil, Coolant Or Fuel: Oil or coolant leaks and unburnt fuel can coat the sensing element and degrade its response.
• Thermal And Mechanical Stress: Repeated heating/cooling cycles and vibration shorten sensor life or crack the sensing element.
• Wiring And Connector Damage: Corrosion, broken wires or poor connections result in faulty signals or intermittent operation.
• Exhaust Leaks Or Engine Problems: Exhaust leaks upstream of the sensor or issues causing abnormal combustion can lead to premature failure.

Opting for a correct-fit Lambda Sensor 1618Q5 ensures proper integration with the engine management system and helps restore drivability, reduce emissions and maintain fuel efficiency on Citroën C1 and Peugeot 107 1.0i models.