Toyota Repair: one month & $300 later engine & VSC back on, air fuel ratio, vacuum leak

Question
Hello Mr Ritter, It hasn't even been a month since I had the check engine light & VSC light come on 2002 RX 300.  I had the o2 sensor replaced (89465-49075) Now today they both came back on. I went back to Auto zone & had a print out (P1150) last time it was P1135. Definition: Air/fuel ratio sensor circuit range/performance, malfunction (bank 2 sensor 1). Probable cause: 1) fuel pump, injector or pressure regulator fault, 2) vacuum leak on engine, 3) faulty AF sensor heater circuit, 4) failed AF sensor. Am I being taken by the auto repair shop? This seems very strange 22 days ago I have the same problem then it was (bank 1 sensor 1) 1)open or short circuit condition, 2) af sensor heater relay fault, 3)failed AF ratio sensor. Could they have done something to cause this & get more money out of me? I'm a single senior citizen, I just can't believe this! Can you please help me?

Answer
Hello, the P1150 code is as you know AF sensor bank two sensor one, the other code 1135 is for the sensor on bank one which is on the firewall side of the engine, bank two is located at the front near the radiator which is the code you have now, these sensors are a very common failure and so I'm not surprised that this one went out after the bank one sensor was replaced.Most repair shops replace them both at the same time especially at higher mileage.