Where do you plug in the obd2 scanner on a 2003 GMC envoy. I think I read that it was somewhere under the dashboard.

a VW car.
no country told at all just ,wow, hard hard questions
it is a smog device, so no the same the world over.
we(USA) have no such car here, so it may not have USA OBD2 ports. (real)
and if in UK(must I guess:?)then OBD2 for Petrol began.
began 2002 up. and 2007 up for diesel
those are approx. ask make for these service manual for exact car and country and VIN,and get the truth
the tool is called scanner.
and OBD2 (our invention)standards the port. here.
other countries copied the design and or parts of it.

a partial list is here, from our top USA maker of scanners

https://www.scantool.net/blog/how-do-i-know-whether-my-car-is-obd-ii-compliant/

ask VW this, or ask a shop in town to scan it and stand there watch him and ask if it is obd2. ???
or buy the book,
in say UK they call it EOBD. and some need a wired only adapter to fit our USA OBD2 scanners. 9 to 16 pin.?
our invention not only sets the protocols and rules
but also the 16pin connector, and sets location of it.

the obd2 location is in the cab, 1meter or less from driver.
what your countries does, is only found in your country
ask them.
before OBD2 was OBD1 here in USA and the connector is anywhere they wanted to put it cab/bay, and is not a standard at all, no 2 car makers the same for OBD1, at all
totally different (ALL)

you need to hook up an obd2 scanner to the port under the steering wheel and see what your computer says which sensor or circuit is acting up

free service at my local autozone or advance auto parts stores

The P0305 code is indicating that there is a misfire of cylinder number 5. This could be caused by a bad spark plug, bad coil pack, injector, poor compression.

The engine light is on whenever there is an issue with the vehicle. To reset the light you would have to fix the problem and then clear the code with a scanner otherwise the light will come back Just resetting doesn't fix it.

Are you plugging into the obd2 diagnostics port under the dash or the diagnostics port under the hood? You should be plugged in under the dash to read codes for the MIL / ABS light. Just a heads up as well most scanners you can buy from the part stores do not have the necessary program protocols to read European cars.

OBD2 engine code PO105 is Manifold Absolute Pressure/Barometric Pressure Circuit Malfunction

3 Options !

1st : Go to your local GM Dealer, they will read the Code to know what's the defective or broken part on your vehicle !

2nd : Go to a Local Garage who do maintenance on vehicle they will do the same as the dealer !

3rd : Go to a local store that sell's automotive product and part's you could buy your own Obd2 Scanner, would cost depending between 70-150 $ but you don't need to buy the most expensive one ! To read the Check Engine Code, will tell the P0... code !

It will not time the vehicle,it is already programmed into the vehicles e c m .

No, to display fault codes set by the ECU you will need an OBD2 scan tool. This vehicle is OBD2 compliant and that is the only way to access the fault codes.

Most consumer available scanners read OBDII on 96 or newer vehicles. If your car does in fact have a OBDII plug then all you need is the software in your scanner to be able to read OBDI codes...a 95 is running OBDI. Advance Auto or Autozone might have a OBDI compliant scanner for free...just tell them you have the OBDII port so they don't take up all your time digging for the adapter!