What is the code? There are lots of thing that can cause O2 and catalytic efficiency codes when the O2 and catalytic converter are in working order. Wizechatmgr outlined them, something messing up the fuel/air ratio or preventing fuel from burning efficiently. 1st o2 sensor(upstream) can't throw ca...

Cheap copper ones single prong NGK or BOSCH properly gapped...or original triple prong Volvo plugs.

Cap & rotor must be Bosch.

Chip in the key in for cars from '96-'99 communicates ONLY with immo control module under the dash via antenna ring around ignition lock. '96-'99 car ecu just need a "green light" from immobiliser control module. '99 and later have coded ecu along with immo box and it's totally different p...

I don't know details but skilled tuner/flasher will know how to fool it...but...either way...Immo unit MUST be in place and connected!
"Green light" is encrypted...so i don't know details.

Now check ECT connector from wiring harness side and check both ECT sensors resistance with a multimeter.

But you should have two o2 sensors.
Volvo Ect is SWF(Valeo)....only aftermarket i would use is Vernet.

They are chipped....those ones are chipped.
Transponder is built in plastic case.

That's how they supposed to be out of the box.
Don't worry.

Yes you can,but you will not have a roll-over protection from fuel escaping anymore.

It's the same part across '96,'97,'98 na & turbo...t5 from '95.....every one with whole assembly replacement part. Inserts for earlier models & '99 are different.
Bosch # 0 280 217 107 up to '99.