The lambda sensor measures the oxygen in the exhaust gases and lets the ECU meter the fuel: as it ages it becomes "lazy" and the mixture stays rich. The result is high consumption, emissions out of limits and a catalytic converter under stress.
Front and rear sensor
- Upstream (before the catalytic converter): controls injection. If faulty, consumption and emissions worsen immediately
- Downstream (after the catalytic converter): monitors the converter's efficiency. If faulty, the typical fault is P0420 with no real driving problems
Typical symptoms
- Increased consumption with no apparent reason
- Rough idle, hesitation under acceleration
- Strong smell from the exhaust
- Fault codes P0130-P0141, P0171, P0172
- Car failing the emissions test at the MOT
What to do
- Have the sensor's live signal read: a lazy sensor is recognised by its slow oscillation
- Rule out intake and exhaust leaks before replacing
- Use quality parts: cheap universal sensors often give signal problems
How MasterTuning helps
We check the component with real measurements, not by elimination: flow rates, pressures, corrections and signals read directly from the ECU. We repair, replace and recalibrate the software when needed. Centres throughout Italy.
Want an accurate diagnosis? Contact MasterTuning and book at your nearest centre.
Frequently asked questions
How long does a lambda sensor last?
Roughly 100,000-150,000 km, but oil consumption and poor-quality fuel degrade it sooner.
Does the lambda sensor affect fuel consumption?
Yes, a lot: it is the sensor that regulates the amount of fuel injected in normal driving conditions.
Can you drive with a faulty lambda sensor?
Yes for short distances, but with high consumption and emissions, and a risk of damaging the catalytic converter.
Faulty lambda sensor: symptoms, fuel consumption and fault codes: what are the symptoms?
The most common symptoms are: increased consumption with no apparent reason; rough idle, hesitation under acceleration; strong smell from the exhaust; fault codes P0130-P0141, P0171, P0172; car failing the emissions test at the MOT.
