2004 envoy service engine light on. Tried to check with scanner for code no power at scanner connecter. could this be a fuse? If so where would it be located?

You may have some fouled injectors. The fault codes need to be read first to determine the cause of the rough running. Check underhood fuse panel fuse #13. This fuse runs the cigarette light as well as provides power to the OBDII connector.

Rob, when the battery is disconnected for any reason a couple of things happen, and frankly it's a design error on the GMT360 platform (Envoy/Trailblazer). Your mechanic did not make an error here. Issue #2, your vent actuators blew out when the battery was re-connected back up, it happens, it's common. Issue # 1 is a little more complicated. The flashing light means misfire, is a seperate issue and a coincidence. Pull the codes out with a scanner and report back, may be bad coil pack, happens and is common. Idle problem and starting to die is an easy fix, betting it only happens when the AC or defrost is on. Disconnect fuse #10 and #28 under the hood. Remove the throttle body and clean it with a sensor safe spray like Seafoam. Drive it around for the computer to relearn the newly cleaned throttle body. Idle problem will be fixed.

You need to go to a auto parts store like Autozone, they will read the fault codes for free and provide you with a printout of the reason for the check engine light being on.

The power for the OBDII connector is the same as the accessory power receptacles, check fuse #46 in the rear fuse panel.

Is your "Service engine soon" light on?? If so, have your vehicle's computer scanned for error codes. If not, Clean or replace the IAC valve (idle air control valve). This unit controls airflow through the engine while the gas pedal isnt pressed or A/C is powered on.

Our mechanic said we need to replace the computer! The cost will be $1,000.

need to have system checked with a scanner to get trouble code Auto Zone or Advanced Auto parts will do that for free if you have one around you

need to scan for codes and find problem code some part stores do for free

You need to check the fuel injection system, throttle body, sensors, check harness for ground. Best solution is to have your engine scanned using Tech 2 scanner. The mechanic will advice you based on the scan code. Whenever the "service engine soon " light the computer system logs the error code. You can retrieve this error code using a scanner.

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.