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Oxygen/lambda sensors. Was Skoda sensor problem.

Just writing out my findings in a seperate thread so that the results can be found easily by future sufferers of apparent sensor failure in the hope that it might save someone a few (hundred?) quid.

My SOSkoda's symptoms were that it did not like starting when warm and would rev up to ~2500rpm all by itself when being driven. I suspected a faulty sensor but as there's quite a few of them, and the cost of new ones was more than the car was worth, it just sat on the driveway, looking sorry for itself.

Thanks to this group, and BRISkoda, I started taking things apart and found that the lambda sensor wasn't working as it should. It's supposed to generate a voltage between 0.1v and 0.9v from cold to hot respectively, which falls away quickly when the heat is removed. I unscrewed the sensor from the exhaust, clamped it in a vice, connected a multimeter, and heated the tip with a blowtorch. The voltage *eventually* rose to 0.8v and slowly fell away to -0.2v (minus!). After trying this a few times I noticed that the results were improving so I played the torch all around the tip of the sensor for a few minutes, especially into the three vents, and tested again. This time the voltage shot straight up to a steady 0.9v and fell very quickly to a steady 0.1v when the heat was removed, which is exactly what it's supposed to do.

I was advised that the water temperature sensor is a common failure point so removed it to test. NB This is the sensor for the ECU, commonly placed in the inlet manifold, not the sensor for the interior temp. gauge. Dunking it in hot water showed it was flashing a resistance for a split second then showing open circuit at any temperature so a new one was bought from the very nice chaps at Evans Motor Factors in Wales ( snipped-for-privacy@btconnect.com), after a search on eBay, for £10.50. I tested the new sensor and it showed a steady resistance.

The car now runs properly and seems back to its normal, horribly basic, noisy, but incredibly useful, self.

So, instead of a 'mechanic' telling me I need a new cat, lambda sensor and temperature sensor and charging me loads, it was all cured for £10.50.

Definitely worth a try as the whole job was quite simple - I just didn't know what results I was looking for until I was told.

Si

Reply to
Mungo "Two Sheds" Toadfoot
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Your running / pooor starting problems would be caused by the coolant temp sensor being duff. NOT the 02 sensor directly. High fuel consumption and emissions failure would be though.

Tim..

Reply to
Tim..

Yes, I believe so too, but if I tested the O2 sensor first I got to play with my blowtorch :)

Si

Reply to
Mungo "Two Sheds" Toadfoot

LOL!

About 50% of o2 sensors can be brought back to life (for a period at least) with the hot blow torch method, but in 50% of cases, getting the sensor out of the manifold usually knackers the threads, so you cant put the old one back anyhow.

Tim..

Reply to
Tim..

If you put a sensor in the vice and connect a multimeter you will only read a resistance, it cannot generate a voltage.

The voltage comes from the car's 12V supply and the change in resistance produces a voltage change to the ECU.

Reply to
PSOE

Err no. I suggest you go and read up on how standard Zirconia o2 sensors actually work..

Tim..

Reply to
Tim..

"Mungo \"Two Sheds\" Toadfoot" wrote in news: snipped-for-privacy@pipex.net:

Glad you got it sorted - great result for a tenner!

Stu

Reply to
Stu

PSOE wrote in news:es930c$ip8$ snipped-for-privacy@north.jnrs.ja.net:

No. The 12V supply is purely for the heating element to allow the sensor to start working quickly. The actual sensing part contains a Zirconia electrolyte and does indeed generate an electrical charge.

Stu

Reply to
Stu

Yes it can.

And... no it doesn't.

Apart from that, ta.

Si

Reply to
Mungo "Two Sheds" Toadfoot

Clarification here is needed. The above is not true for a Zirconia sensor, A zirconia sensor can produce a voltage off the car if heated up, via a torch, to its working temp and oxygen is excluded in the process. Apart from the heater side, zirconia sensors are not dependant or have a measurable resistance.

TITANIA sensors are different. They do not produce a voltage but change a supplied voltage via an internal resistance change.

I believe a very few older Skoda's used a Titania but as far as I know all modern ones use Zirconia.

Regarding the recent fuel crisis I think that the cars that have exhibited problems will only be the tip of a very big iceberg. The main ones affected seem to be late Vauxhall's, Peugeots and Merc's. For example its now nearly impossible to buy a sensor for a 2002 Corsa with the Z20XE engine but no problem getting them for the up to 2002 X20XE engine.

I believe that the engine management of the later cars are much more dependant on the lambda sensor signal than the earlier ones and therefore a duff sensor makes a big difference to driveability. If the problem is silicone poisoning then there are going to be 10's (possibly 100's) of thousands of cars with duff sensors where the ECU is more tolerant to a nil lambda signal as far as drivability is concerned but come MOT time there will be major emission problems. Graham

Reply to
Graham

How?

Except it does exactly that.

Reply to
Conor

The Zirconia sensor is based on an electrochemical fuel cell. It generates a voltage in a similar way to a battery.

That's a Titania sensor.

Si

Reply to
Mungo "Two Sheds" Toadfoot

Conor pretended :

If you have an old style gas valve with pilot light on your heating system, the gas valve is held in not by voltage from the mains, but by a tiny voltage generated by a thermocouple - the thermo couple tip being placed in the pilot lights flame. Exactly the same principle as the lambda sensor, but for the much higher temperatures involved.

Reply to
Harry Bloomfield

Don't think so Harry.

I understand entirely the principle of the thermocouple - dissimilar metals in contact with each other create a potential difference when heated. However, what is wrongly described as a "thermocouple" in heating systems is actually a tube of liquid (usually alchohol) in a sealed system that expands when heated, thus holding the flame failure device off.

It is totally non-electrical in every sense of the word.

Chris

Reply to
Chris Whelan

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