Exhaust Gas Emissions Control
With so many vehicles in use on our roads, the reduction of pollutants produced by the internal combustion engine is of ever-increasing importance. To encourage advances in technology that can bring this about, governments have progressively introduced tougher exhaust gas emission legislation. Lambda sensors are an integral part of the emissions control system required to reduce exhaust emissions.
Cambiare, the aftermarket specialist in vehicle electronics, has close to 600 lambda sensors in its range, with over thirty five parts added recently in December 2014. The range now covers more than 5,000 applications with the new to range additions. With four types of sensors, namely, Zirconia, Titania, Planar and Wide Band within its range, Cambiare gives a detailed update on the form, function and working of lambda sensors.
Understanding the Lambda Sensor
Lambda sensors (also known as oxygen sensors) are devices fitted to petrol and diesel engines that measure the oxygen content of exhaust gases. The purpose of the sensor is to help the engine run as efficiently as possible while producing fewer emissions.
Air to Fuel Ratio
The combustion of fuel within an engine occurs due to a mixture of air and fuel, ideally in the ratio of 14.7:1 in a petrol engine and 14.5:1 in the case of a diesel engine. This ratio is also known as the stoichiometric [pronounced: stoy•key•o•met•ric] ratio or Lambda (λ) where the mixture has a value of 1.0.
During combustion, the ratio of air to fuel mixture varies. This can create the following situations:
• Less air would leave residual fuel after combustion, known as a rich mixture. The unburned fuel in a rich mixture creates pollution.
• Excess oxygen intake, caused by the presence of more air than the stoichiometric ratio, creates a lean mixture. A lean mixture tends to produce more nitrogen-oxide pollutants and in some cases, it can cause poor performance and even engine damage.
Understanding the Mechanism
The lambda sensor is positioned in the exhaust pipe and can detect rich and lean mixtures. The mechanism in most sensors involves a chemical reaction that generates a voltage. The engine’s computer (ECU) looks at the voltage and adjusts the fuel injector output accordingly, so as to bring it closer to the stoichiometric ratio (λ).
The lambda sensor must be hot enough (around 350°C) to generate a voltage signal. Modern vehicles are equipped with sensors that typically have 3 or 4 wires and a small heating element that aids in attaining the high temperature faster. The heating element also prevents the sensor from cooling down too much during a prolonged idle state, which would cause the system to revert to open loop*.
(*Open loop is when the ECU eliminates the lambda sensor from its calculations)
|0.9V||Rich mixture||ECU ‘leans’ air/fuel mixture by reducing
amount of fuel in engine
|0.45V||Equilibrium point of 14.7: 1/ 14.5:1,
based on engine type
|Balanced output; no action|
|0.1V||Lean mixture||ECU makes air/fuel mixture ‘rich’ by increasing
amount of fuel in engine
Older, single-wired lambda sensors do not have heaters. Care should always be taken to replace worn sensor with an identical one. When the lambda sensor fails, the computer can no longer sense the air/fuel ratio, so it estimates the required quantities. This leads to poor performance and excessive fuel consumption by the vehicle.
One-wire and two-wire unheated lambda sensors rely solely on hot exhaust gas to heat them up to operating temperatures and are designed to allow a large volume of exhaust gas to make contact with the active ceramic element, exposing them to contamination. They should be checked or replaced every 30,000 to 50,000 miles.
Much less exhaust gas needs to contact the ceramic element in heated sensors, making them less prone to contamination. Heated sensors can also be located further downstream (closer to the catalytic converter) which increases their life expectancy. They should be checked or replaced every 60,000 to 100,000 miles.
Faults & Failures
Constantly exposed to the harsh environment found in an automobile’s exhaust system, the lambda sensor sustains a constant barrage of harmful exhaust gases, extreme heat and high velocity particulates. Sometimes contaminants such as coolant, oil or silicone particulates find their way to the sensor, contaminating it and rendering it inoperable.
A lambda sensor’s life is long, in some applications up to 100,000 miles. But its effectiveness will inevitably decrease over time, either by contamination or normal use. A worn sensor can cause unacceptable emission levels, affect performance and ultimately damage the catalytic converter. Therefore lambda sensors should be checked at each service.
• Cambiare lambda sensors are precision-made for outstanding performance.
• OE quality, BER compliant parts.
• 100% direct fit.
• Manufactured to meet or exceed all original equipment specification and test requirements, enabling:
• Improved engine response and performance;
• Lower emissions and improved fuel economy;
• Longer sensor life.
• 2 year or 30,000 miles warranty, whichever comes first.
• Technical helpline 0845 543 8280*
• Same-day delivery from FPS.
Cambiare offer even more
• Exhaust Gas Pressure Sensors: a sensor that either measures the pressure just before the DPF or relays the difference between gas in the intake and outlet of the DPF. The evolving EGPS range covers key applications like BMW 520d 2.0 (03/2010>), Audi A4 2.0 (11/2007>) and Mercedes-Benz C220 2.1 (12/2008–01/2014).
• Exhaust Gas Temperature Sensors: a thin film platinum sensor that monitors exhaust temperature during regeneration and can help prevent thermal overload. The new-to-aftermarket EGTS range has around 80 parts and covers popular applications such as, VW Golf 1.6 (02/2009–11/2012), VW Passat 2.0 (03/2005–07/2010) and SAAB 9-3 Sport 1.9 (04/2004–07/2012).