Thank you for choosing JustAnswer and allowing me to help you resolve your Toyota questions!
You can get the malfunction codes read for free at most parts stores in most states. They do this as a free courtesy to sell you additional parts. If the vehicle is running well enough with no cylinder misfire or flashing of the check engine light you should be fine to drive it to the parts store to have this code read. Once you have the code number post it back here and I can give you some additional information. 90% of the time if the engine is running normally the malfunction code is related to the emission control system. On this particular Van if you have a P0420 code which is very common it means the catalytic converter has failed.