August 19, 2022

Car Spotter / Blogger / Reviewer

Car Lambda Sensor

An important component of a car that most people are blissfully unaware of is the oxygen lambda sensor.

The sensor is placed between the exhaust manifold and the catalytic converter.

In newer vehicles, there are 2 lambda sensors. The second sensor being located right behind the catalytic converter.


What is a lambda sensor probe for?

To make sure your engine is burning fuel correctly, a lambda sensor measures the output of oxygen in the exhaust fumes.

Back in 1977, to prevent and reduce harmful emissions including carbon monoxide and environmental pollutants produced by cars to conform to Government compliance and regulation, the sensors are in place to keep car engines running as efficiently as possible by tracking and adjusting the oxygen levels and alerting the driver when the outputs deviate from normal readings.

Since then, lambda sensors have become widely used.

They are also known as oxygen sensors or O2 sensors.

How does a lambda sensor work?

When a car burns diesel or petrol in the engine, it mixes with air to create the most efficient operation of the engine.

To optimise the air and fuel mixture, the lambda probe sensor adjusts the fuel amount sent to the engine cylinders, which ensures the engine is working optimally. In turn, this reduced the harmful gas emissions rate by making sure the catalytic converter is working correctly.

European regulations on pollution and CO2 emissions mean a lambda sensor is the critical component to keeping your car adhering within these regulations.

The lambda sensor is physically placed before the catalytic converter. It is programmed to measure the amount of air and fuel in the unburnt exhaust hydrocarbons after combustion. The information is sent to the car’s computer, the Electronic Control Unit (ECU) which controls functionalities of the engine and will adjust the fuel mixture accordingly.


A couple of phrases used to categorise the air and fuel mixture:


Running rich

Too much fuel in relation to air ratio. When the fuel is said to run rich, there is an oversupply, excess of unburned fuel. Unburned fuel creates pollution and harmful gases.


Running lean

On the opposing side of the spectrum is the phrase ‘running lean’ This is when there is too much air in the fuel mix. A lean fuel mix creates more nitrogen-oxide pollutants. It also leads to poor engine performance and potential damage to the vehicle engine.

The Bosch lambda sensor and how to install it

Bosch Lambda Sensor has a black plastic electrical socket on one side, and a thin wire connecting to the metal cylinder which fits into the exhaust system. The lambda sensor typically lasts between 50,000 and 100,000 miles depending on conditions.


Tools required:

  • Safety glasses
  • Socket wrench
  • Oxygen sensor socket and scan tool
  • Professional installers may also require DBOM or Bosch Scope
  • Floor jack and jack stands or vehicle lift



  1. Locate and count sensors by following the exhaust pipe, usually before and after the catalytic converter
  2. Follow the wiring harness until you reach the wiring connector, disconnect, and push the tabs, pulling the harness apart
  3. Using an oxygen sensor socket or open-ended wrench, remove the oxygen sensor from the exhaust pipe
  4. Before you install the new Bosch oxygen sensor be sure to clean the threads of the exhaust pipe after removing the old sensor with a wire brush. Do not add any anti-seize compounds to the threads, this is already done by Bosch for the part.
  5. Insert the new sensor and hand tighten the sensor, using an oxygen sensor socket or open-ended wrench tighten the new part on the exhaust. Tighten another half turn or until snug.
  6. Don’t overtighten as the heat of the exhaust will swell up the threads.
  7. Re-attach the electrical housing clip to the vehicle


For a full walkthrough, see the extremely useful YouTube clip of the full process below:

Bosch Auto Parts - Replacing an Oxygen Sensor

Car Maintenance , Vehicle safety

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