Volvo: 855 t5 eating coolant temp sensors, coolant temp, water coolant

Question
Hi Guys
At wits end with my car (volvo 855 t5) , I've had it to dealers twice in the last few weeks with a failed water coolant sensor, first time it went got all kinds of strange problems revving engine lights fading ABS light on so took it to volvo who read code 123 replaced the temp sensor and all was well for 2 weeks, dreaded lambda light came on (no symptoms car was running perfectly) so I pulled over switched off the engine cooling fan remained on car would not start again, the AA arrived 90 minutes later and the car started no problems, temp gauge went to 3 o'clock cooling fan ran constantly, drove to volvo no problems whatsoever other than cooling fan running constantly, volvo said "ok maybe a faulty sensor" they fitted a new thermostat and a new sensor and sent me on my way all was well for a month then exact same thing happened light on cooling fan stayed on, so I bought a sensor myself and fitted it, it ran for 15 mins before wrecking the new sensor, checked all the wiring apart from a tiny nic in the wire at the connection all seemed ok, tested the voltage coming from ECU and it reads around 5 volts, Volvo now want to fit a new ECU although they admit that this might not be the problem, anybody got any ideas, or should I go for ECU replacement.............please help I love my T5 dearly

Answer
Hello John! That is very very strange problem. However, I have seen it before. As long as all wiring is ok, The ECU is the most likely cause. I am curious though, what other faults if any, were stored besides the 123 code? Just make sure the dealer does a wire by wire fault trace before you replace the ECU.

Jimmy