328i Lambda probe heating error code

[B234R]

I´ve got an issue with my 1996 328i OBD I (European spec). Almost a year ago I plugged INPA to my car and pulled a error code "25 Lambda probe heating Probe 1". Analog Values 2 graphics showed that, while oxygen sensor 2 voltage oscilated between 0-5 V, oxygen sensor 1 voltage always stayed in the 4,80-4,90 V range. The car drives fine (although since I bought it 4 years ago the engine, frankly, doesn´t seem anywhere as creamy as I expected a in-line six should be, or as my E39 530i), idles perfectly, good performance and fuel economy.

Yesterday I had the annual inspection and it failed the smog test, the CO values were very hign and worse in the second try than in the first one. This afternoon I´ll plug INPA again but it seems the oxygen sensor 1 need replacing.

Question is, is it advisable to replace both oxygen sensors or replacing only the bad one will be enough? OE BMW or a NTK sensor is fine? Very difficult to do? I suppose that if it´s screwed in the header the cold/hot temperature changes will make it hard to remove.

Thanks a lot.

[Eric93se]

Yes replace both, NTK/NGK/Denso. It's not a hard job, but there is a tool that assists in getting the old part out. You should also use injector cleaner every so often. Here in the US we have a product called CRC GTP that will help clean the system out (crc guaranteed to pass, google it). If you can't get it then just run a quality product over a couple tanks of fuel, use good gas. You should drive a couple tanks of gas with cleaner before re-testing.

- - - Updated - - -

search ebay "oxygen sensor tool". I don't know what size it is though.

[B234R]

We have CRC products over here but I´ve never seen CRC Guaranteed To Pass for sale. I could try and use a good injector cleaner like Liqui Moly´s, and see if I´m lucky in the smog test, but if it fails I would have to pay the inspection test cost again. It´s not very expensive but it´s about half the price of a new NGK oxygen sensor, so the sensible thing seems to replace at least the bad one.

Thanks!

[B234R]

New oxygen sensor installed, I passed the smog test with flying colours. Great!