O2 sensors. Replace one or all?

[RandallNeighbour]

My local shop is suggesting I change out all four O2 sensors because one is sending a message to the computer and giving me a check engine light.

Any advice? My boxster is a 1997 model with a new engine in it (probably no more than 5k on it) I have no idea if they changed out the O2 sensors when they replaced the engine... that was before my time.

[Tool Pants]

If the engine was replaced by your Porche dealer then you should go back there and see if they will help.

[RandallNeighbour]

the engine was replaced by a previous owner. I bought the car from a Miami dealer who bought it at auction.

Assuming that the sensors are not all new, should I go ahead and have all four replaced? They're 160 bucks each plus 2.5 hours of labor to install them.

[Tool Pants]

The sensors are not replaced when an engine is replaced. You need to know the fault code(s) to determine if it is a sensor and which one or ones are causing the check engine light. Does your shop have a PST2 or are they using a code reader.

[RandallNeighbour]

My mechanic only had a code reader.

The second shop I called, who specialize in Porsche repair, told me to go ahead and replace all four as they will all go soon enough... but who knows when the others were replaced? It's a seven year old car with a couple of unknown owners.

I also found out that the camber on the back wheels is as far up as possible on one rim and as far down as they can go on the other, making me think something's awry with the sub frame. Smells like $$$ to me!

I guess this is turning out to be a project car, not a dream car.