Got a temp sensor fault on my Escort GTi, when I bought the car it was constantly reading full temp, so I changed the sensor and it was fine problem solved, then about three weeks later it went dead, wont read anything at all, but I noticed that this is only when I have the engine running, when I turn the engine off, but turn the ignition on it goes straight to max temp then if i turn the engine over it drops dead again, is it the sensor thats fucked or is there soemthing else going on?

cheers.