Weird electronic “hum” while parked

1. Key-off monitor This monitor checks for EVAP (evaporative emission) system leaks and canister pump module malfunctions.

The monitor starts 5 hours* after the ignition switch is turned off. At least 5 hours are required for the fuel to cool down to stabilize the EVAP pressure, thus making the EVAP system monitor more accurate.

The leak detection pump creates negative pressure (vacuum) in the EVAP system and the pressure is measured.

Finally, the ECM monitors for leaks from the EVAP system, and malfunctions in both the canister pump module and purge VSV based on the EVAP pressure.

HINT: *: If the engine coolant temperature is not below 35°C (95°F) 5 hours after the ignition switch is turned off, the monitor check starts 2 hours later. If it is still not below 35°C (95°F) 7 hours after the ignition switch is turned off, the monitor check starts 2.5 hours later.

 

Dm93, thanks for the detailed rundown of this function. I was worried for a few minutes!

I heard an unusual vibration noise coming from the fuel tank area of my new Tacoma while working in the garage this afternoon, and thought the fuel pump turned on by itself. I quickly grabbed my keys, turned the ignition to ACC and it stopped. A quick search on TW returned this thread. Relief! I am glad to find that this is a normal function of the 3rd Gen.

 

Yea alot of people are alarmed by it the first time they hear it, Toyota has been using this design EVAP system on many of their vehicles since the mid 2000s.
It's actually in the owners manual as well.

 

First time I heard this phenomenon on my truck was about 30 days after buying it. It almost gave me a heart-attack: Ya: OK: "Here we go!" It must have been most of the way through the process because the show stopped after about 5 minutes. My first thought was: intermittent parasitic electrical gremlin: "No wonder someone traded it in".
TacomaWorld saved my life: looked it up in here and found the cause. I have only heard it one time since: when the truck was parked in my garage. Seriously??? I don't need to hear strange and changing whirring, faint clicking and other misc strange noises coming from a vehicle with no key in it: when it's parked in my garage under the house! Uncalled-for and it makes me nervous.

Damn engineers! They did this on purpose and are still laughing their butts off to this day ten years later reading the freaked-out posts about it in TacomaWorld.

Or maybe it's just me.

 

Yea I'm not sure why Toyota (and some others) use a Leak Detection Pump instead of Natural Vacuum Leak Detection like most of the domestics use, NVLD systems are certainly much simpler to diagnose but I can't say they are really more reliable.

 

It's funny you mention that. I was just thinking I should read the owners manual yesterday while driving home. My '15 SR base was as simple as it gets, but there are so many features on this '23, I don't have a clue how to use/remove them.