Toyota Repair: camry not shifting to O/D, 2002 camry, camry

Question
I own a 2002 Camry for some time now the car wouldn't shift into O/D when cold, but it would after it warmed up for a short period of time. it does have 175,000 miles on it. hoping to fix this problem I changed the filter and fluid in the transmission last year. that made no difference. Now the problem is getting worse it only goes into O/D seldomly. The fluid isn't burnt or discolored. hoping that it may be some sort of faulty shift module. Any ideas your help would be greatly appreciated

Answer
First thing to do is to make sure that the engine reaches operating temperature, overdrive will not engage until the engine is warmed up to about 170 degrees, it seems too long to warm up replace the thermostat, also make sure the coolant fans are not staying on all the time.