Reputable Nissan Mechanic (Dealer maybe?)

What year is your Xterra?. If you go to Santo Domingo Motors (dealer), they will charge you at least 10K or 15K DOP for a "full" service. Depending on the mileage, a service could be very complex or very simple, but definitely don't take it to the dealer unless money is not a problem. For the check engine light, I think you're better off getting any unexpensive scanner from Amazon ($20 to $30) and finding out yourself before taking it to a mechanic. That way you'll know if they are telling you the truth (My bet? Catalytic Converter. Gas is very low quality here)

You can try this guy, Alexis 809 7655735, located at the corner of Jose Contreras and Mahatma Gandi, Gazcue. At least he will not rip you off, he is a honest guy (very rare in DR!). He can do the most of the work, but you need to ask what parts he is going to use, because if Dominicans say that they will replace a sensor with a new one, they mean that it's new to your car, but usually it's a used part that they buy in Villa Juana.... so if you want new parts to avoid the same problems again in a month or two, just say clear that you want NEW parts installed. Regarding the check engine light, he has OBDII scanner, after he scans the codes from your car, you can write them down and google Nissan forums to see what people there say about those codes, this can save a lot of time and money. Sometimes it's not clear what cause the error, so before paying money to do possibly unnecessary work, check the forums first.

The check engine light can be on because of different errors. On older cars you can ignore most of them, if the engine is still running normally, for example catalytic converter errors or oxygen sensor errors on 1996?2000(or 2002) cars are common, but may affect fuel economy a little, nothing serious. On modern cars things are more complicated, because every error can change the way how engine computer operates the engine and it can result in rough idle, running too rich, smoke from the tailpipe, reduced engine power, etc.... there is no cable between accelerator pedal and throttle body on modern cars, so in case of any errors coming from the pedal or throttle body sensors, the engine computer can put the drivetrain to the special protected mode, and the car will not shift from the 1st gear and will not run more than 15-20 mph. It's a pain in the ass if it's happens while you are driving from Punta Cana to Santo Domingo All modern radiator fan clutches are controlled by electronics too, so the clutch can lock up permanently and produce a lot of noise, or if it can't lock when needed, it can result in overheating. For all of these and many other problems you have just one signal light, the check engine light. You never know why it's on on modern cars, there are hundred reasons for this. So, if it's a modern car (2002 and on), instead of disconnecting the battery in order to try to turn off the check engine light, I recommend to pull the codes from the computer as soon as possible to see why the light is on.