Exhaust & emissions · Sant Andreu
Lambda sensor: diagnosis and replacement
The lambda sensor measures exhaust oxygen and adjusts the engine’s mixture. As it ages, the car uses more fuel, pollutes more and lights the warning. We measure, confirm, and replace the right one.
What does this service include at Tallers Marathon?
Each sensor’s real response measured, leaks ruled out, and replacement with an OEM-level unit.
- Response measurementAn ageing sensor responds slowly long before logging a fault code.
- Exhaust leaks ruled outA leak upstream of the sensor skews the reading and mimics its failure.
- OEM-level sensorDubious-quality cheap sensors cause more problems than they solve.
- Mixture verificationFuel trims checked after the change.
What are the symptoms of a failing lambda sensor?
High fuel consumption, juddering or unstable idle, fuel smell, the engine light, and a risk of ITV failure on emissions. A lazy sensor can raise consumption noticeably without ever lighting the warning.
The lambda sensor is one of the few parts that pays for itself: an aged sensor enriching the mixture can mean noticeable extra fuel over thousands of kilometres. In older engines, replacing it usually restores original consumption. That said, a "sensor" code is not always the sensor: a manifold leak, a cracked hose or a dirty airflow meter produce identical readings. Our routine: measure the sensor’s response, rule out leaks, and only then quote. If the error coexists with a catalyst efficiency code, they are diagnosed together on the catalytic converters page.
Frequently asked questions
How many sensors does my car have?
Modern petrol cars have at least two per exhaust line (before and after the converter); diesels use wideband sensors and additional probes. Diagnostics identifies which one is failing.
Can I fit one from the internet myself?
The usual risk: cheap sensors giving out-of-spec signals and recurring codes. Some are also seized, and without the right tool the exhaust thread gets damaged.
Does the sensor affect fuel consumption?
Directly: it is what adjusts the mixture. A slow or drifted sensor enriches the mixture and consumption rises with no other symptom.
What if the code returns after changing it?
Then the cause was something else (leak, mixture, wiring). That is why we measure before replacing — so you do not pay for parts that were not the problem.
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