Faulty O2 sensor, which one?

7 - 8 months ago my engine warning light came on. After a mild panic and a trip to my garage they told me the O2 sensor was at fault. After reseting the system I was told to try it for a few days to see if it came back on.
Months on it has now come back on. I can easily replace the sensor but which one???
I have found a place to get DENSO replacements. The short wire manifold sensor for £55 and the long wire cat sensor for £66.
After replacing the faulty sensor will the engine light go off automatically or will I have to get the garage to reset it for me, or is a simple disconnect the battery?
(oh it's a M13a engine)

do you know the fault code?

Unfortunately I don't have a code.
I don't have a diagnostic wotsit to plug in.
I am currently trying to fathom out if I can get the code using a wire shoved into a plug under the glove box.

I had this problem on my Grand vitara. Had a mechanic freind do it. I think generaly the first one, along the exhaust, goes first. And if i recall you need to have a code reader to turn the light off. I could be wrong, the grand vitara was a bit more advanced than the humble Jimny.

Nobby

X-Eng Simon wrote:
Behind the glove box you'll find a six pin connector. The diagnostic computer plugs in to this. However, by shorting two of the pins (2 & 4 IIRC) it will flash the engine warning light to indicate what fault codes it sees. Disconnect battery for a minute to reset the codes once you've fixed the problem.
There is lots of info on line about the connector and codes.

This helped me diagnose a faulty cam pos sensor.

Si

Just found this. Will give it a go tomorrow.

www.rhinopower.org/diag/cel.html

never had to disconect battery before once the fault is sorted light should go out