Toyota Repair: 2001 sienna van code problem, car computer, ecm

Question
i had the o2 and converter changed in 2007. the van is 6 cyl. my ck engine light went on again.the dealer said the codes are po420 and po773. they said to replace the car computer for $1600. the car has no symptoms except the light.the van has 125000miles. ideas???????

Answer
Toyota did issue a service bulletin that addresses the P0420 code, it requires replacing the ECM with an updated part, the warranty is for 8yrs/80,000 miles. Toyota also issued a service bulletin for the 773 code which also requires replacing the control module,it seems their diagnosis is correct.