e-manage is OBD compatible since e-manage is just a piggyback on the stock ecu. But as before, you can just plug your stock back in as long as you haven't boosted your car. PFC has no OBD compatibilty so it won't give OBD error codes. PFC is nicer for the GTS esp the 02 since you can adjust the rev limit. On at GTS with the PFC you can adjust lift engagement but I don't think it's useful to be able to do this. On PFC you can adjust the vvti and on the e-manage you can't. PFC has higher resolution than the e-manage on the fuel and ignition maps. But then again the same *others* may say that XS sucks and can't tune shit haha. But the XS engineering Turbo kit does come with a PFC. Some *others* will probably say the PFC just takes more skill to tune correctly.ouch hehe. Some have said or implied it is easier to tune a Turbo Celica with the e-manage than the PFC. I highly doubt the stock ecu (you plugged back in after you took out the PFC) will adjust very well to a Turbo. If you plan on Turboing your Celica and if you have smog tests in your area, you might lean toward the e-manage so you have a shot at passing smog. give your stock ecu some time and distance to adjust before you test.say at least 40 miles in various driving conditions to be excellent. You can just take out the PFC and put your stock ecu back in (2 minute job) and your car will probably pass as long as your other upgrades are CARB approved. E-manage CAN be smog aning it is possible to pass a functional test and tailpipe test with it installed and tuned (not technically legal to use in some states or all maybe.but then again they'll never know unless you tell them).