Lambda sensors: 4.2XKR 2002
 

I'm running on propane - no problems, and good value here in the UK, where petrol is not exactly cheap. About 9 months ago I replaced a lambda sensor, but at the latest service I was told that the other 3 are all showing errors. However, the emissions are within legal limits.

This is not making a lot of sense to me, as I would have thought it extremely unlikely that 3 would fail at once. The propane people say that it cannot be anything to do with the conversion; another mechanic has suggested that I may have an air leak somewhere. Any thoughts on this, anyone?

Not sure how many miles you have but these sensors do have a finite life. It would be helpful if you could say what exactly the error is, or if there are any particular codes associated with them.

If you don't have a check engine light on then it probably isn't an outright failure but more likely that the sensor range is degrading and the technician made a note of it.

An small air leak won't cause a sensor problem, as the system will adapt to the new air volume and adjust the short and long term fuel trim to compensate, at which point the sensor should show normal.

Thanks for this, Charlie. The engine check light does come on even though, as I said, emissions are within normal range I don't know what the codes are at the moment. Car has now done about 90k miles - it seems to be running well,

You'll need to get the specific error code but they should be accessible with any common code reader. In the US most auto parts stores will read them for free, not sure if that policy carries over to the UK.

100k, give or take, is the service interval for an O2 sensor. I call it that because, while we tend to think of them as fixtures, they really are a consumable and need to be replaced periodically, in much the same sense that spark plugs do.

They are heated to get them up to operating temp more quickly, and it could be that heating element is what has failed, rather than the sensor itself. In the same vein, the heater is on its own circuit, so you might check the fuse too. 30A in the engine control fuse box, one fuse for each bank (upstream and downstream share a fuse).

...yes, this is useful information. With the mileage now over 90k I suspect that it must simply be age. As I said, the vehicle starts and runs well, with no change to fuel economy (economy, on an XKR!!) - but part of the mystery is that the engine light is on and emissions normal. I'll get them changed at the next service, or before if things seem to be going wrong.

Cheers.