Buying replacement Lambda sensors - info and a question

I have been investigating the sort of o2 sensors used on our cars as I might need to buy one. So of course I have been interested to buy the cheapest I can. Best price so far seems to £75 quid all in.

Anyway...

Previously I said the ones on my car were wideband sensors. I assumed this because the output voltage range was 0 to 5V. But I was wrong.

In fact they are (both) 4-wire heated narrowband titania sensors. These ones are a newer sort not used by too many manufacturers (good old volvo - makes them even more expensive ). Used mainly by Volvo, vauxhall and some beemers.

Anyhow the traditional zirconia lambda sensor produces an output voltage between 0 to 1V. Around 0V for mix to lean, around 1V for too rich and a big step around the stoichiometric ratio.

The titania sensor is also a narrowband sensor which produces this step. But it does not generate a voltage and instead its resistance varies. Around 0 ohms for mix too rich and around 20kohms for too lean with a big step between resistances.

These sensors are driven with a voltage signal and from what I can work out the ECU must implement a potential divider with the lambda probe forming one half of the divider. But this is where it gets interesting, because - and this is weird! - the voltage measured from the sensor is different for phase 2 and phase 1 cars!

Well, at least for the phase 1 T4 the voltage range is 0.. 5V: high voltage (around 5V) for a rich mixture and around 0V for a lean mixture (this is for front sensor, rear one is about 0.2V to 4.8V). So this means the sensor must be the top half of the voltage divider, supplied with +5V with the lower half pulling the thing to ground being a reference resistance.

But on phase 2 T4 cars the voltage range is only 0..1V: high voltage (1V) for rich and low voltage (around 0V) for lean. So for phase 2 cars it behaves just like a traditional zirconia narrowband sensor.

I know the above because it says so in VADIS. Also on my car I measure the 0..5V sensor range.

Anyway the following might be useful for those needing a new lambda probe:

FYI, for these titania sensors it is possible to use a universal sensor since they require no external "air vent": provided good, weatherproof connections can be made then one can re-use the existing connectors. The standard wiring for a titania sensor is as follows:

Red: +ve supply to heater
white: -ve supply to heater
Black & Yellow: Supply & Return to probe sensor (effectively a resistor)

And our sensors (from sensor to connector) seem to confirm to this.

For reference, the wiring to the sensor connector (for both is on the bulkhead behind the cover near the VIN plate) should be as follows (according to the Volvo wiring diagrams):

Both front & rear sensors are supplied by the ECU with a common connection, it is marked "ground" but I suspect (on my car, at least) it will be +5V (will check at some point). These cables are white/black.
The sensor return cables are yellow/brown or yellow/grey.
The heater +ve supply is shared, both red/black.
And the heater returns to the ECU are violet or green/white.

When buying new sensors, anyone 4-wire titania sensor seems to be ok: but it must have an 18mm thread (needs 22mm socket). Here are some part numbers which are useful (NOTE - these apply specifically to my engine B4194T2 but are probably same for your s/v40 non-GDI petrol):

(Note - if you buy the genuine sensor it comes with the right connector and the right length of wire, otherwise re-use existing connector and re-make wiring)

Front sensor
Genuine replacement - Bosch: OTA4F-5C2
Genuine replacement - Lucas: SEB363
Universal - Lucas: SEB231
Universal - Bosch: 11022T18
Volvo p/n (B4194T2 specific): 30617337

Rear sensor
Genuine replacement - Bosch: OTAF-5E1
Lucas: SEB362
Universal parts as for front sensor
Volvo p/n (B4194T2 specific): 30864308

Best prices I've found are actually for the genuine ones from here:
http://www.lambdapower.co.uk

However I would say to anyone it is worth looking on ebay etc. because cheaper sensors (maybe £50 or less) do come up, often for vauxhalls, and you can cross-reference other manufacturer's ones to see if they are 4-wire titania sensors from the website I gave above, and if so then they can be used as a "universal replacement".

And now - the question! Re. air/fuel gauges....

For a phase 2 car with a 0..1V output voltage, a narrowband A/F meter sounds just right.

But for my phase 1 T4 with its 0..5V output voltage, is there any reason anyone can think of why a wideband gauge would not be suitable? Although the wideband sensor's voltage won't change in such a sudden "step", surely the only factor for the AFM is the range of the input voltage from the O2 sensor?

Any thoughts on this would be appreciated. And hopefully the above is useful because from volvo an O2 sensor sounds like £!kerching! to me!!!

Cheers,
Pete

[Big T]

I'm lost!!! lol

I know that on s40 concepts I was advised to change my sensor to a wideband one so I could use an AFM gauge, haven't done it but seems a lot of the yanks have!!!

Does that answer your question??

LOL! I've been tom dick lately so I've been stuck inside with nothing to do but write lots on this forum... hence big posts recently

Installing another - wideband - sensor seems ok but I dunno about changing to one that sounds like something to mess up the ECU, wiring different to start with.

But it seems the (true) wideband sensor output is 0..5V same as my car... and probably same as your car too as yours is phase 1...
... but then the wideband AFM are very expensive so hmmm.... still not sure

AFM must be just a high impedance discrete voltmeter anyhow, so one option would be to make one's own. Another option I thought of was to rig something up which divided the voltage from my lambda by four before sending it to a narrowband one. But would need to be high impedance so not to affect the EMS measured readings.

But if you do install one, and it all goes wrong, be sure to let us know so we don't make the same mistake and blow everything up

Pete

[SIAMBLUE]

Pm Engineer, he is the man too talk too,

Gary,

[Big T]

Originally Posted by peteS40

But if you do install one, and it all goes wrong, be sure to let us know so we don't make the same mistake and blow everything up

Pete

Cheers lol!!!!

[steve00117]

Haven't tried them myself but, www.crankshaftsensors.co.uk may be worth a call.

[4 forty]

this seller has 2 different types,at £16 and £18.

http://cgi.ebay.co.uk/NEW-Universal-...QQcmdZViewItem

petes40??

paul