Will not start after battery was installed backwards?

The first thing I would do is a CAN scan which will tell you which modules are not working. Here is a video to show you how. You can get a CAN scanner (Controller Area Network) which will work on most cars from Amazon.

here is a video to show you how:

https://youtu.be/u-4syLc-ifQ

Here is a guide that can help as well:

https://www.2carpros.com/articles/resolving-reverse-battery-connection-in-cars-a-step-by-step-repair-guide

You might have shorted out the access/start authentication module or the instrument cluster. Please go over these guides and get back to us.

Dear Ken,

Thank you for the suggestion. I borrowed a scanner from AutoZone and tried to hook it up. I connected the battery correctly, pushed the brake pedal and the start button, and waited for the scanner to finish. My start button is on the console, not on the steering column. The car did not start. The car screen displayed "Key not in Range" and a yellow "Steering Issue" light. The scanner eventually gave me a Communication Error, and it would not connect. I changed batteries in the fob but got the same result. I was watching some videos on YouTube, and someone fixed the "Key not in Range" problem due to a broken wire going to the ignition switch. Maybe some wire there got burned?

Yes, that can be, but usually the wires don't burn, it pops fuses and blows out modules, I would turn the systems on and then recheck the fuses, this guide will help:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Also, did the scan give you any code numbers? If so what are they? Check out the images (below). Please let us know what happens.

I checked all fuses and relays in the engine compartment and fuses on the left side of the driver's seat. I replaced a few fuses in the engine compartment, including the multifuse. These tasks were done before I tried the scanner. I will check all fuses again to see if they are still ok. I did not see the fuses and relays that you show above in the trunk and under the steering column. I will look for them again.

Sounds good, let me know what you find.

Dear Ken, I was able to partially access the electrical panel nearest the steering wheel. The two components I could get to without removing the entire dash are a 506 (part 561907413) and 507 (part 7N0951253). They were the parts closest to the floorboard. The 507 has a circuit diagram on it, but the 506 does not. I'd like to test the 506, because I think it may be bad. The terminals on the 506 have a cloudy white surface, unlike the shiny terminals of the other relays. Also, I can't find a parts dealer with the 506 relay in stock. Any advice? Thanks!

Good find, you might need tom get a used relay by searching ebay or wrecking yards. Have you tried searching google for the part?

Hi Ken, I tried a quick search on google already, but not extensively. I will search in more detail. Thanks

Sounds good, let me know if it fixes it please. Also, did you get any cods out of it?