Highlander Alarm System Siren Fault

I had a similar issue with my 2012 Opel Astra. The error was also stored in the error memory, and the alarm system was completely inactive. Did you check the cable and plug connections? That was the problem with my Astra.

Where exactly should I be looking for the cable and plug connections? Is there a specific location for the alarm controller or a common fault point?

On my Astra, the issue was with the connection to the siren itself, which was near the wheel arch. But on your Highlander, I'm not sure where it is located. Given the error, it's most likely a defective cable or plug. It is probably best to have it checked at a workshop to avoid further damage. My visit to the workshop cost only 95€.

Thanks, I appreciate the suggestion. I'll take it to a workshop and have them check the wiring. Hopefully, it's just a loose connection like you suspected. They found a defective plug connection and fixed it.