94 buick lesabre engine shut down while driving on the highway today.had this yesterday and my mechanic placed on diagnostic scanner.scanner reads rr module problem.i do have code as for its not listed on my billing invoice.

Sorry to say, that is one of those GM cars that is difficult to retrieve trouble codes without special scanners. It was on some '94 and '95 GM luxury or upscale models (your LeSabre was one), where they put in the new diagnostic connector that became standard on all cars built after 1996- and called OBD-2 (for On Board Diagnostics, second generation). The problem is, your '95 model is typical of all early '90's cars and trucks equipped with the OBD-1 system. It only has 2 digit trouble codes, and there are not a lot of them, only about 2 dozen in total. The whole system is OBD-1, but the diagnostic connector is configured like an OBD-2 connector.
Some shops might have the scanners necessary to work on your car, some with high end scanners. Of course, GM dealerships would have the right testers, but they are outrageous in prices.
I would try to find someone who could get the codes for you. What you describe sounds to me a lot like a bad Mass Airflow Sensor, or MAF sensor. That is just a guess, though, and why I recommended you try to see if there are trouble codes. There should be at least one.

I think the mechanic could very well be right in this case

check the fuel pressure from fuel pump it may be bad. its a possibility that the coils maybe getting hot and shutting down engine. but check the fuel pump relay in fuse box. to see if this is your problem. it could be getting hot and shutting down, just replace it.is the check engine light on ! if so you can go to auto-zone and they will scan it for free of charge. to find problem code. with OBD-II scanner. good-day !!

Run a diagnostic scan to help troubleshoot---Fuel pump or crank sensor would be a good place to start guessing.

check for corrosion on the sparkplug wires, both ends. Crankshaft position sensor, cam position sensor and lastly, gulp, the ignition control module..

If the service engine light is on, it could be a faulty sensor or anything electronical with the car. It may even be something non noticeable. The only way to check exact problem is to run error codes.

Has the fuel filter been chg. lately. If it has, maybe a fuel pressure test is in order. Fuel pump might be geeting weak and does not show up until it gets warmed up. Fuel pumps are a common problem on this type of cars.

Sounds like what is called shutter changing to synthetic fluid fixed my 98 Lesabre

Do you have check engine light on???if so scan it OBD 2 yue$$ding isn't the way to go,if you don't have a check engine light on then perhaps coil pack!!! coils do run intermittent some times! and not trip the eng light on !!!!this would be a great place to start.Hope this helps

Hi! If it seems to be much worse in the rain, why don't you have a mechanic test your engine for codes and functions after he rinses your engine down with water? Water won't hurt your engine. Good luck! Jack