There are two fuses that give power to the ALDL. Those are in the lower fuse panel on the left side of the dash. They are fuse 1 (constant power to pin 16) and fuse 29 (switched power to pin 9) The first one is usually what powers a scan tool. However, that fuse powers more than just the ALDL port so it's likely not the problem. However, it's easy enough to test them. You need a simple test light connected to a good ground. Take the test light and with the key on touch it to pin 16 and then to pin 9. It should light up on both. Now test the ground pins at 4 and 5. To do that take the same test light and connect it to battery power, either using pin 16 or the battery itself and use the light to probe pins 4 and 5. The light should come on in both. If all 4 of the pins test good for power and ground the port is likely not the issue.
If you are plugging a scan tool in and it powers up but cannot connect then that would be a different issue and could be the wiring to the PCM or a bad PCM. If you are plugging it in and it isn't powering up, then try it on another vehicle and see if it powers on in that one. If it does and the other tests show that there is power and ground then it could be the connector pins are not connecting properly but that isn't common unless someone forced something into them and spread them open.
Images (Click to enlarge)
Saturday, October 8th, 2022 AT 1:28 PM