99 Silverado engine light on cannot get a code from odb reader

Likely a transmission code the reader cant see. Suggest you try a better $$$ reader.

You must connect an ODB-II code reader to determine what codes are stored (which will also indicate what has failed in your car that caused the Check Engine light to illuminate). Once you have repaired the defects, the ODB-II code reader may be used to reset the stored code condition.

After fixing you sometimes need to delete the fault codes that er registrered on your ECU "electronic control unit, or car computer". You do that by using the ODB device and on that device select to delete fault codes.

check your water, oil, belts if that is good go to a Autozone parts store
O'Reillys auto parts there other stores these are the ones I use. ask if
they can do a code scan to why the check engine lite is on.

You need a reader that can cancel the trasnmission codes. Look to Advance or one of those parts places. Call to ask them if their ODB tool can cancel Transmission codes first before you go there.

have you had a odb 2 compliant reader attached to compilment that? it could be as little as a gas cap not sealing. i suggest using a code reader to assure your money is spent wisely.

if you can find the plug m8 yes usually in drivers foot well behind dash or unders ashtray or panel under handbrake

You have an ODB-II port under your dash. Autozone or some other of the same sort would be happy to connect their code reader and to tell you the codes, no charge. Of course, they would also be happy to sell you a code reader, but that certainly isn't necessary.
Hope this helps you.

My ford expedition 99 has service engine soon light on. Hooked up to ODB and the equipment showed nothing; no power; checked on different car worked fine. what is cause. Equipment has worked on another ford expedition before by the way.

Your car has a OBD2 hook up under the dash somewhere on the drivers side, You have to have a computer to hook up to that ODB plug and reset it, If you live near a Autozone they will clear the code for you for free, One other thing you try is disconnecting your battery for about 30 mins, that works on alot cars to reset the check light.