OBD II Port Doesn't Work

I'm going to leave this here because I didn't find this exact fix on the internet. If anyone has additional info, please add!

OBDII port doesn't work in Stormin' Norman, my 2012 TRD Sport. Smog Check station computer won't connect and they won't smog my truck. (!!) I get one red light on my BAFX Products ODBII Diagnostic Interface and it never connects via bluetooth.

What the Internets says: It's either the wiring, fuse, or ECU
My Fix: Use a powered scan tool

Troubleshooting steps:

• Check your scan tool or cable. Someone had a bad Scangauge cable. Try the scanners at a smog shop, auto parts store, or dealership.
• Check the ODB fuse. It's in the engine bay, on the driver's side. Fuse #7. It's 7.5 amp. Some people have said to the 20A EFI fuse in position 19, but if that's blown you have bigger issues. Anyway, I checked all my fuses, even the ones inside the cab.
• Check the wiring between the port, fuse box, and ECU.
• Unplug battery for 30 seconds, plug back in.
• Try a powered OBD scanner. Some take batteries and supply their own power. That was my fix!
• It might be a bad ECU (booo!)

Story: I accidentally left my bluetooth scanner (BAFX Products ODBII Diagnostic Interface) plugged in for months during the pandemic when I wasn't driving very often. Apparently that can drain the battery, but I always got a strong start. Went to get smogged and the guy said his tool couldn't connect to my truck, but he'd done five smogs that day, so he doesn't think it's his tool. No computer reading, no smog in California. Go home, confirm my scanner doesn't work either. Check wires (they look brand new), check all fuses, #shititstheecu#. Go to the Toyota dealership and he can connect fine! Huh, What? Did they reset the battery? He offers to do smog. Go for it. Call back - smog wasn't working but we tried "stuff" and you passed. I want to know what happened, but Never Question A Pass. They perform recall 20TC01 - Air Injection Pump and Air Switching Valve. They don't reinstall my custom air filter on the air pump - the fix I did because I knew that was the air pump issue.
When I return to pickup the pickup the tech was super helpful. Basically his handheld ScanTool has a battery and supplies it's own power. The smog machine normally doesn't, but apparently there's an optional battery port - when they used that it worked.

Conclusion: I still don't know why non-powered scan tools used to work and now don't. Something's obviously wrong. I'm bummed my BAFX dongle doesn't work anymore because it's saved me over $1,000 in repair costs. Apparently there are two pins on the OBD port that supply power, but finding and troubleshooting those will have to happen another day. If anyone knows please post.

 

Grab a meter and check your OBDII power. Pin 16 to ground (Pins 4 & 5). If you don't get a full 12.5ish volts across 16-5 and 16-4, you have a problem.

 

Just to add to this, the 7.5A OBD fuse is what supplies power to the OBD2 connector. Ckeck for voltage at the fuse. Check for voltage at pin 16 with the negative lead on a good ground point. If you have power there, then check the pins 4 and 5 for functioning ground.

 

My scanner would not activate. As Muddinfun mentioned - check the 7.5A fuse. The only thing I could figure was I blew it when jumpering 4/13 with a paper clip to set transmission fluid level.