Replaced battery now radio and alarm not working

Question edited for clarity.
Question moved to model category.

Both the radio and the alarm drain _some_ power when the car is off. The radio to keeps its memory of saved stations and the PIN code, and the alarm is fully activated and monitoring when the car is switched off.

The most likely item to drain would be the alarm. It is the factory alarm or an after market add on?

The first thing to do is have the battery load tested for efficiency. Any Interstate Battery shop will do this for you free of charge in-car and takes 2 minutes and give you a print out of the CCA on the battery and what the tester diagnoses.

It appears that it is a known issue on this vehicle!!

https://www.google.com/search?q=2003+toyota+avalon+parasitic+battery+drain

..

Radio has to be reset - designed to not work any more if battery is disconnected. Theft protection.

PIA.

Go to dealer for code.

Most all aftermarket radios have their own fuse next to the wiring harness plug. Depending on the brand, it may only take a few minutes to pull the radio out of it's sleeve to check for the fuse. Usually, you can pop off the trim ring to see what you are working with.

lock your door and hold the key in that position, and then turn it the other way and hold it until they roll up, this should set the alarm back. If that doesnt work try replacing the radio with the stock one, your third option is to bypass the alarm module.

You need the radio security code.

I hate to say this, but sometimes they're all connected on a shared ground circuit; and in your case the shared circuit happens to be underneath the hood on the front of the left side fender. Now, there is another ground for the security hood switch. As far as the check engine lamp coming on, it may be a wsie choice to take the vehicle to have the ECM checked for any lingering codes. AutoZone has a free service for scanning engine codes.

slow cranking of the engine by the starter indicates low battery voltage, did the battery light come on in the dash?

hello,for your radio,you need a radio code,if you don"t have ask your dealer to provide the code,alarm system is always activated when you lock the vehicle,ty

Check the fuse in the car for the power windows and alarm in the car if blown replace them....And also check the battery..


Good luck...

need to have car battery ckeck for voltage drop...if ok...put ingition key in run position for twenty four hours and recode radio..