Q: When one outer tire rod goes bad do you need to replace all the other 3?

There is a test protocol in the factory service manual that is relied on to determine if a tie rod end is "worn out". Per the protocol, if it turns out that only 1 tie rod end is worn out, then only that one need be replaced and the others can be left alone. In practice, though, these parts (particularly the outer tie rod ends) will usually wear in use and so if one is obviously unserviceable, most mechanics will replace tie rod ends as a pair. Technically, such replacement in pairs is not required but the economics are such that if the mechanic is already there, it is cheaper in the long run to replace both particularly as a vehicle wheel alignment is mandatory after each replacement (i.e., imagine replacing one tie rod end, paying for an alignment and then 6 months later replacing the other tie rod and paying for yet another alignment; not economical, of course). Finally, tolerances in alignments these days are extremely small. So, if there is frankly any wear at all in the unreplaced tie rod end, it is quite literally impossible to align the car to the factory settings (we are talking about tolerances on the order of .020 inches, for example). To have the tie rid ends on your steering system evaluated and replaced, as needed, please request tie rod end inspection/replacement and the mechanic will let you know of the best approach for you given your unique circumstances. If you have further questions or concerns, do not hesitate to re-contact YourMechanic because we want you to make the most of your repair dollars and help you to get the best possible results.