2003 Buick Park Avenue - My service light is on and one mechanic said I needed to replace the fuel sending module. What does that en-tale and do I have to drop the fuel tank?

Ask your mechanic if he is absolutely 100% sure this will fix your SEL issue, yes, the whole module is in the fuel tank. But in my mind, iif the fuel sensing unit was faulty, it would'nt trip a OBDii code. Maybe if there was a leak, such as a loose gas cap or the fuel pump gasket failed. To answer correctly, we would need to have the 4 digit codes or codes that were pulled by your mechanic. It could be as simple as trying a new fuel cap, to a sensor, or gasket, to something else. Really hard for us to give you a definitive answer here.

What trouble code(s) do you have? -Jim

I will find out in the morning if the mech will return my call. I know he said the original code was the O2 sensor, but when his supervisor went deeper after replacing the O2 sensor, he said it came from the sending unit in the tank.. More later I think.. But I thank you for your quick response.

I did replace the gas cap1st originally, then the O2 sensor

Thank you... I am off to the garage tomorrow to get another reading of the codes. Will jot them down and let you all know the results!

You can actually visit your local auto parts store and have the computer scanned. Most stores will do it for free. HTH. -Jim

I finally had Advance Auto do a read as follows: 1. C1214 System Relay Contact of Coil Circuit Open 2: C1223 CR Wheel Speed Sensor input is 0 3. C1224 Right Rear Wheel Speed Input equals 0 4. C1248 Electronic Brake Control Module Turned on the Red Brake Warning Lamp 5. P0420 Catalyist System Efficency Below Threshold bank 1 I was told the Brake Module was bad, but I do not need that to pass inspection so much as the Check engine light indicated an error code P0420 Does that give you guys enough to offer suggestions other than junking the car ? Thank you in Advance

P0420 basically means that you need a catalytic converter. Check rockauto.com for a universal one. But first check the emissions decal under the hood and see if you have California Emissions. If you do you must get a converter that is C.A.R.B. (California Air Research Board) compliant. If you don't, the code will reset with the new converter. I live in NJ and both my '00 Grand Prix and '03 S-10 Pick up have California Emissions. However my '08 Grand Marquis does not. So check that sticker. In December of '13 I replaced the converter on the Grand Prix. I got the converter from rockauto.com and had a muffler shop install it. Total cost was about $400 including a new resonator which I bought from the muffler shop. HTH. -Jim