I can't figure out why a bad catalytic converter would cause the stability/traction control to stop functioning, but others have reported this as well. That doesn't seem like good design on Toyota's part.

The bad converter does turn on the check engine light, though, and that reminded me of advice I've heard from several sources: If you've got the check engine light on, read the standard OBDII trouble codes and look at that stuff first.

Code readers of several types are getting cheaper, and I think it's a good idea to have one if you're going to do much of your own work or if you hope to learn more to protect yourself from incompetent or dishonest service departments. If you've read the code yourself you can sometimes stop the service folks from selling you a load of something you don't need. Also, the code readers can often be used to reset the check engine light to see if the problem was a isolated event.

The regular code readers can't do everything that the Toyota-specific testers (typically at dealerships) can do. That includes programming new keys and reading or resetting a bunch of Toyota-specific parameters. Fortunately some of that Toyota-specific stuff can be done by manipulating pins of the OBDII connector and watching lights in the instrument cluster. Instructions are in the service manual, and you can get temporary access through alldata.com if you don't want to buy those expensive volumes.

All this applies to the pre-CAN bus 4Runners. I don't know if things changed after the bus protocol switch--maybe others who have the service manuals can enlighten us.