On those not-quite-infrequent-enough occasions when I have to have automotive repairs done, I search for TSBs: Technical Service Bulletins, those handy addenda to the factory service manuals that cover the problems that weren’t necessarily anticipated beforehand. (My subscription to Alldata’s online manual includes all the latest TSB updates.) Sometimes — not always — they’re the next-best thing to a recall, because they indicate that the automaker knows about this problem and has a fix that doesn’t require hours upon hours of hyperexpensive diagnostics: if A and B, then perform C.
There exists, in fact, a TSB for Gwendolyn’s minor indigestion: if code set=P0420 and drivability issues=none, then there are two choices for C: if the ECU is not at current release level, flash its little EPROMs; if the ECU is at current release level, replace one particular oxygen sensor (of four) and the front pipe assembly.
It was the latter in her case, so she’s getting new hardware. The front pipe, I regret to say, contains all the pre-catalytic-converter stuff, and costs more than the actual cat. (And since it’s not the actual cat, it’s not covered under the Federal emissions warranty, and yes, I took this up with the service manager; force of habit, I suppose.) Still, I feel vaguely better paying for real live parts than I would paying for a lot of part-swapping and other guesswork.