I started my 2004 Sienna AWD Limited and there were two indicator lamps: VSC and Malfunction Indicator Lamp. I brought it to a Toyota dealer who said they he read two codes off the car: PO420/PO430 and that they indicate that the catalytic converter needs replacement. I asked if there was any other diagnostics to be sure, and he said that it was unambiguous: those indicator symbols and the codes mean that the catalytic converter needs replacement, immediately, to ensure no damage to the car. Is this correct? Should he have done any other diagnostics. Could these codes mean anything else?