Code reader not coming on whe i plug it in on a 94 gmc sub cig lighter works

Easiest way to find out if its the fuse, is to look at the fuses with a flashlight and see if any of the links are broken. If there are any blown you'll see and you should replace the ones blown. That should tell you which one is connected to the CIG lighter. If you don't find any are blown then your CIG lighter connections behind the actual CIG lighter might be loose.

Look at the wires coming into the radio, check for an inline fuse.

Well it could. Or something as simple as the cig lighter fuse is blown.
Do you have spark to the plugs ?

You'll have to get the scanner or code reader to work. Make sure the cig lighter fuse is good. Once you get the trouble codes you can proceed.

You need to look at which fuses operate the OBD 1 scanner. Alot of times you will find out that it is connected to the cigarette lighter. So the lighter must work first.

{: ) There are two fuses that protect the front IP power outlet or lighter plugs. At the underhood fuse block, labeled CIG LTR 15amps and AUX PWR 20amps. See red arrows on diagram below.
The fuse on the driver side door fuse block labeled AUX PWR2 20amps protects the rear lighter plugs.

The Sierra may possibly have a blown fuse.Typically the lighter or accessory ports power the OBD II connector.

check all the fuses. if used alot it will pop the fuse. should be i think is 15 or 25 mini fuse. best of luck

you most likley have a blown fuse. the fuse for the connector and cig lighter are usually on the same circuit . if you have a owner manuel check and see which fuse is for the obd/cig lighter. if you dont have a manuel then check every fuse in the box and see if you find a blown one. the plug whare the scanner connects is what powers the scanner so if you cant find a blown fuse then you know youre not getting power to the plug for some reason.

remove the ashtray and reach behind the cig lighter you should feel a nut you take the nut loose and the cig lighter comes right out just unplug the wires and plug them on to the new one. and if you get your new cig lighter first you will get the idea of what i am talking about the nut