Toyota Corolla

Please help me isolate whats wrong w/ my toyota corolla's temp gauge. The temp gauge quickly rises way above the full scale in a span of 5-10 seconds after turning on the ignition.I already replaced the temperature sender but still has the same response, what else could be wrong?

Thank you very much
February 28, 2007.

The gauge itself could be bad or you may have a coolant leak somewhere.
Pressure test the cooling system to eliminate that as a cause. Hook up a scanner to see what the ECM is reading as the coolant temp.

Mar 1, 2007.
Tnx 4 the advise sir. I'm sure there's no leak in the cooling system. Cooling fans and thermostat valves also are functioning well.I'm thingking of abnormally high voltage being read by the gauge.I took some reading and the voltage rises from about 9v-12v in just 5-10secs. I also checked the gauge, I found a couple of 1w 27ohm resistors and a 3v zener diode sticking on the gauges' body, a simple ohmeter reading confirms the resistors are good, but the zener diode shows some abnormal (almost short)readings. Could this be the faulty component? But i'm thingking, if the zener is faulty, temperature should rise instantly and will have no delay. But anyway, i'll try and replace that. I also found out that the gauge has 3 connectors, one for the B+ supply, the other from the the temperature sender, but do you have an idea where the other wire is connected? (Body ground maybe? I'll appreciate it if you can give me any diagram on how the temp gauge is connected to the cars's electrical) and what is an ECM? Thank you very much sir for the help you provided.

Mar 2, 2007.