2006 GS300 - Issue with car jerking/slipping when coming to a stop got diagnosed as a Transmission problem. Transmission was replaced and issue still happened so original transmission was put back in and told it could be ECU issue. Then suggested I reset the ECU before attempting to repair or replace it. So ECU reset attempt was done by pulling the 2 ECU fuses (1 on drivers side and 1 on passengers side). Fuses were fine and put back correctly but now the car has ZERO power (no lights or anything) and won't jumpstart either. Battery is 1month old and clean terminals.

What is causing the car to have no power and not jumpstart?

 

Check the fuses you pulled and inspect the contacts in the fuse box.

 

I already did, they're fine

 

Sounds like you popped the fusible link, it is the main fuse that controls the power to the vehicle. It usually pops when you accidently reverse the wiring or arc positive.

It is located in front of the battery and its a long strip. You can use a jumper wire temporarily just to verify it is bad.

This is what they look like
https://www.ebay.com/itm/19283710168...EAAOSwzyFgdOtL

 

As for the transmission, it is common for the 2006 GS300 (only that year) to have transmission issue from there module located inside the main ecu. You can send yours out to have it examined and repaired for $100 at SIA electronics, you can find them on ebay. They do most of the repairs for members.

Heres a link
https://www.ebay.com/itm/22397146009...YAAOSwu4haz235

 

Only 2 fuses were pulled for 25min and put back in, there was no accidental reverse wiring of any kind.

 

You removing the fuses to ecu reset, is no different then you just removing the battery terminals. Check the voltage on the fusible link that I showed, put a test light on both sides of the positive terminal. If only ones side "the battery side" lights the test light and not the other then you have a bad fusible link. This fuse, is the main fuse for the whole vehicle. Think of it as the main breaker bar that controls a whole house, once it gets trigged, everything shuts off.