Well, you will be relieved to know, it isn't because there is a fault with the stereo.
Volatile Memory: What's it got to do with car stereos?
Volatile memory in car stereos refers to the ability of the system to retain settings and data when the power source is disconnected. This memory ensures that your stereo doesn't reset every time you start your car. The yellow and red cables play pivotal roles in maintaining this memory.
Yellow Cable: Constant Power Connection The yellow cable is conventionally connected to constant power, usually directly to the car's battery or a power source that remains active even when the car is turned off. This connection allows the stereo to retain settings, presets, and other crucial data. It's akin to a continuous trickle of power that sustains the stereo's memory.
Red Cable: Switched Power Connection In contrast, the red cable is typically linked to switched power or the ignition system. When the car is turned on, it supplies power to the stereo, activating its functionalities. This configuration ensures that the stereo operates only when the car is running, preventing unnecessary power drainage when the vehicle is off.
What should I do about this?
Well, the below photo shows a standard ISO loom that works with Pioneer stereos.
You see that yellow and red cable? Disconnect the cables at the bullet connector and swap them over. Red to Yellow and Yellow to Red.
In a lot of European cars like VW, Audi, Skoda, Seat, Peugeot and Citroen, these cables are the wrong way around so the stereo is not receiving permanent power, only switched live power. Swap these cables over and you are good to go!