Lambda sensor

[watling3654]

I have a 2008 Berlingo 1.6 diesel van with the engine management light just come on,has slow acceleration and using a little more fuel. The book and google say lambda sensor which I have just bought,the trouble is I can’t find the old one to replace it.the book says either on the cat or the manifold,had them both off today and can’t find the lambda sensor anywhere.looked the length of the exhaust and it’s got me stumped,anyone know where to look or point me in the right direction.thanks

[jj9]

Diesels don't have lambda sensors.


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[watling3654]

Diesels don't have lambda sensors.


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O that might explain why I can’t see one,will ring the auto parts shop who sold me one for my vehicle.phoned 2 shops who both could supply me going of my reg number,might have to sauce a code reader see what that tells me,thanks for the help.

[jj9]

Actual I'm wrong, some diesel engines do use a lambda sensor (O2 sensor)...well I never.... I've never seen one but Google tells me they do.

If your van is a 2008 1.6 hdi diesel I don't believe it has one.

Take a look at https://www.catcar.info/citroen/?lang=en&l=

Put your VIN number in and see if you can find an O2 sensor for your vehicle, I can't see one for any of the 1.6 hdi's.


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[watling3654]

Thanks for that will look into it,just got an obd code reader to see if that is the problem.but my thinking is with you and not one there,or if there is it’s part chameleon.

[Sol]

I think the difference depends on whether a CAT is fitted as with later diesels after a certain date. CAT's need pre and post O2 sensors so the ECU can adjust the fuelling to maintain the correct levels of pollutants that the CAT can deal with by passive action.

Basically if it has never had a CAT (too early), then it should not have O2 sensors. As JJ says most diesels before a certain date were not fitted with them (CATs) but later on they started putting them on all engines. Unlike Petrol's which have them by law from about 1993 onwards, diesels were much later to be fitted with them as standard.

[jj9]

Zion do you not mean DPF ?


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[Sol]

No mate, the DPF of course uses differential pressure sensors to measure flow, and check for blocking (like air handling systems do) but they started fitting actual CAT's to diesels at some point, integrated with the DPF in most makes now, but not all. The CAT operation can only be determined by the post-cat O2 sensor showing improvement of oxygen levels compared with the pre-cat sensor but I am not sure how its actually handled on the Citroen version. I know the early 2000's VW SDi Caddies had CATs as I removed mine and this was way before DPFs became widely used.

Lambda control seems to only be used on HDi engines anyway due to the higher injection pressures and finer fuelling control. It seems perhaps a main wideband Lambda is fitted and is used to control smoke on part-load, unless full throttle is applied and then the ECU uses smoke maps only.

From the AA website:
On diesel cars, the diesel oxidation catalyst is often integrated with the Diesel Particulate Filter (DPF). Catalytic converters (CATs) have been fitted in the exhaust of the majority of petrol cars manufactured since 1992 and diesel cars since 2001.

From LambdaPower.co.uk
High-pressure common rail Diesel injection
The first automotive common rail fuel system was developed by Denso of Japan, and used for commercial vehicle applications. The most popular system in passenger vehicles, developed by a group of companies including Fiat, then sold outright to Bosch, is termed variously (CDi, HDi, TDCi, DCi, for example). High-pressure common-rail injection represents the current state of passenger car diesel systems. All of the combustion phases detailed previously for the low-pressure injection systems apply, but different methods are now employed to overcome some of the problems.

As the name suggests, firstly, the injection pressure is raised substantially, from roughly 300psi in a traditional diesel, to about 2,000 psi at idle and up to 15,000psi at full load. This allows finer atomisation to occur when the fuel enters the combustion chamber due to greater velocity from the injector. Also, rather than the injector being activated by a mechanical pump and one-way valve, the injector is triggered electronically, just like in a petrol injection system. This allows very fine control of spray timing, and allows the ECU to combat some of the disadvantages of the C.I. process.

Diesel exhaust soot is caused by incomplete combustion due to localised lack of oxygen, but with fine electronic control of the injector the ECU can inject the fuel into the cylinder in stages, rather than all at once. This allows a small amount of fuel to initially pre-heat the chamber and finish burning before the main injection charge.

This main charge will then encounter favourable conditions - a higher initial temperature will mean the delay period (Phase 1) will be shorter, leading to smoother power delivery. This degree of control is only practical during part-load operation; during periods of hard acceleration the requirements for a rich mixture are still present, and it is during this phase that most of the soot is produced due to localised poor combustion. However, particulate filters can trap most of this in the exhaust system, which can be oxidised out as required by the ECU, by burning it away at high temperature.

Diesel Lambda sensors
This super-fine control of mixture strength allows Lambda control to be possible for these common-rail systems, and from about 2005 onwards this has become the norm. Motivating all these innovations are EU emissions regulations, which are becoming ever more stringent for Diesel cars after an initial phase of being allowed to lag behind the equivalent petrol-engine regulations.

Diesels are by nature lean burn engines, so require a wideband lambda sensor that can detect A/F ratios over a very large range. Silicone compounds are added to diesel fuel to ease transportation and for their anti-foaming properties, which poisons the lambda sensor over time, but additional measures are taken in the design of diesel lambda sensors in order to combat or lessen this problem.

[jj9]

My car has a CAT but no Lambda sensor, and watling3654's will be the same.

The text you've posted is more or less what I read when I researched Lambda sensors on diesel vehicles, I came to the conclusion they are only being used on the very latest engines in the quest for better emissions.

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[Sol]

Yeah that's all I could find on it.