Everything you need to know about lambda sensors

Lucas explains why lambda sensors fail, how to diagnose issues and offers testing and installation advice

Everything you need to know about lambda sensors
Lucas boasts one of the UK’s leading ranges of lambda sensors.

First fitted to cars in 1977 to improve the efficiency of combustion engines and help to reduce harmful exhaust emissions such as carbon monoxide, Lambda sensors operate by measuring the amount of oxygen in the exhaust.

An efficient engine requires 14.7 parts air to 1 part fuel.

This perfect mixture is called Lambda and is where the unusual sensor name originates.

However, they are often also called oxygen sensors or O2 sensors due to their fundamental role of measuring oxygen.

The levels calculated by the Lambda are sent as data to the ECU which then calculates and determines how best to achieve the ideal mixture of air and fuel at combustion.

Lucas say an incorrect air/fuel mixture will be either rich or lean.

In a rich mixture the air is high in unburned fuel, though low in oxygen.

A lean mixture has the opposite balance and is high in oxygen due to not enough fuel being injected.

In a Tech Assist bulletin, Lucas said: “Many vehicles now feature a pre-cat lambda sensor and a post-cat lambda sensor.

“Whilst the pre-cat lambda sensor communicates to the ECU regulating the air/fuel ratio; the post-cat lambda sensor performs a diagnostic role, monitoring the catalytic converter.

Symptoms and causes of failure

“Before a vehicle fails an emission test or the engine check light appears; drivers may notice increased fuel consumption and/or a rough idle.

“Both are signs of a failing lambda sensor.

“Once the sensor fails the OBD may display either code P0131 or P0134.”

The lifetime of an unheated sensor is around 45,000 miles and 100,000 miles for a heated sensor.

Lucas said: “The lambda sensor operates in extremely high temperatures so damage to the heater element of the sensor is the most frequent fault associated with this part.

“Vibration or damage to connectors and/or wires can also cause failure.

“Another common cause of premature failure is contamination.

“If the Lambda has failed as a result of contamination it is likely that the sensor will have visual clues to the source.

“It is important to analyse the visual appearance and if signs of contamination are present the causes must be addressed before the sensor is replaced.”

afAntifreeze Contamination

With Antifreeze contamination, the sensor nose will be contaminated with a grainy white or light grey coating.

Coolant with anti-freeze may have found it’s way into the combustion process and reached the lambda sensor.

Always address the root cause of the failure before replacing the lambda sensor.

In this case check the head gasket for leaks and repair if required.

lambda-additiveFuel/Engine Additive Contamination

Similar to anti-freeze, the sensor nose will be contaminated with white or red deposits.

Excessive use of any engine or fuel additive can contaminate or block the lambda sensor.

Again, address the root cause of the failure before replacing the Lambda Sensor.

In this case cleaning the fuel system prior to replacement is required.

lambda-oilOil contamination

Oily black deposits left on the sensor nose may be a result of the vehicle burning excessive oil which can contaminate and/or block the sensor.

Thoroughly check the engine for leaks including all the usual seals that are prone to failure. Once repaired replace the sensor.

lambda-richFuel contamination

If fuel is burning too rich, a black soot may be seen on the sensor nose.

A damaged lambda sensor or fault in the fuel system can result in a high air to fuel ratio producing black soot which damages the lambda sensor.

Measure exhaust gases to ensure the fuel system is functioning correctly.

Check the lambda sensor heater control and sensor heater, rectify any faults before replacing the sensor.

lambda-leadLead Contamination

The sensor nose may be contaminated with shiny grey deposits.

Not as common now as this type of contamination is usually caused by leaded fuel attacking platinum parts or the sensor.

Replace any leaded fuel in the system with unleaded before replacing the sensor.

Installation tips

Lucas advises technicians that plugs and cables should be kept clear of heat sources and care should be taken so as not to cross-thread or over torque the sensor.

For vehicles with two lambda sensors, Lucas recommends replacing in pairs.

1. Clean the thread in the exhaust pipe with a cleaning tap.

2. Apply copper grease on the sensor thread only – do not grease the sensor nose.

Although most lambda sensors are pre-greased, the extra grease will prevent thread galling and reduce friction which could lead to over torque.

3. Tighten the sensor to the prescribed torque, using a torque wrench with a suitable lambda sensor socket.

Over torque is especially dangerous when sensors that have a heater element as it could crack the internal ceramic wall causing the sensor to fail.

 

Lucas range of lambda sensors includes over 550 part numbers for more than 6,000 direct fit and universal applications and includes Zirconia, Titania and Wideband sensors.

For more information about Lucas lambda sensors, select ‘more details’ below.

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  • #156320 Reply

    First fitted to cars in 1977 to improve the efficiency of combustion engines and help to reduce harmful exhaust emissions such as carbon monoxide, Lam
    [See the full post at: Everything you need to know about lambda sensors]

    #212070 Reply
    Dave Reynolds
    Guest

    Could you tell me what would be the impact on the Lamda sensors if the inlet flow probe on the Mass Air Flow device had inadvertently not been reconnected after the air filter had been changed? I have a BMW Z3 and the EML warning light has come on and the garage who did the diagnostic check are telling me there is little difference between the output profile on the inlet and outlet sensors from the two
    Lamda sensors and have concluded the catalytic converter is faulty/ not operating. However, it has come to light that the inlet flow sensor to the air filter was not connected and just prior to the diagnostic the exhaust emissions we’re check for the MOT and we’re well within specifications.
    Is it likely that the disconnected inflow sensor has resulted in the Lamda reading that indicate the catalytic converter has not working and that by reconnecting it the Lamda reading should be ok and not indicating that the catalytic converter is not working. Thanks Dave

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