A "test only station" is an inspection station that only does emission inpections/tests, not test and repair. Eventually all will probably be test only because of the incidence of fraud at test and repair stations.

Most M103 engined Mercs are being referred to test only stations because the engine family has been tagged as a "high emitter profile".

The low cost drive through places are test only, and the inspection and test is the same regardless of whether you go to a test only station or test and repair. The test only stations are convenient because many are set up as a production line (like a car wash), so the whole thing only takes ten or fifteen minutes if there's no line.

Back in the seventies and eighties California certification limits were a little tighter than 49 state. The CA ASM (accleration simulation mode) field emission test bogies are the same regardless of whether you have a 49 state or CA certified car. The field test bogies have no direct relationship to the original certification limits. The field limits are established by statistical analysis of all the field test data.

Suggest you search on this topic. There have been several recent discussions about how to "manage" your test to increase your chances of passing. Most M103s are on the ragged edge of failing, and many fail, though the failures are often just marginal. In these cases there is usually nothing really wrong. The owner just didn't manage their test properly.

Duke