2003 avalon 208k miles runs fine . recently without reason alarm went off without any reason to do soat start up after sitting all day. finally got it to quit but if you opened the door it would go off again. at the time the fob was not in use and was not close to the car and hadn't been for long time(end was broke couldn't attach to key ring). this only happened on one day. nothing on the scan tool appeared. hasn't happened again over the next 2 weeks. mechanic cant fix it because he cant repeat problem and nothing was revealed on the scan tool. suggestions to prevent it from happening again? can you disable the alarm? new fob?
only issue is possibly ignition lock might be the problem because you can pull key out on occasions(sometimes) while it runs sometimes not.
thanks for your thoughts
Check the battery connections. As you said, it could also be the the ignition switch.
Find a real diagnostic mechanic. They will download an electrical schematic from AllData, and test the connections for power, ground and the condition of the relays, from the ignition switch to the alarm. Especially if it's an aftermarket alarm (or if there is any aftermarket wiring), well, that is usually very ad hoc and snarky wiring.
My general bet is that its either a ground problem, or a module/sensor problem.
To see how this is done, watch (on YouTube) either wiring detective work by Eric O at South Main Auto or Ivan over at Pine Hollow Auto Diagnostics. You'll see how real diagnosticians go about their work.
