P0155 is the heater inside one of the oxygen sensors (bank 2, sensor 1, it'll be one of the ones on the exhaust manifold rather than after the cats, looks like a spark plug). Grab a used one off eBay and change the plug if necessary (you should find that you can pop the pins out, no need to cut & splice). You'll probably find the universal ones don't work, the fault kept coming back on my sister's Avensis because the heater resistance of the universal one was too low (4Ω, the Toyota ones are around 12Ω).
You don't want Lexus fixing that one, Toyota quoted £240 to replace ONE, and both had gone! I did the pair for under fifty quid, including the special socket to undo it.