I have a 2008 BMW 328i Coupe

I cannot figure out what this rest button is??

I read it has something to do with keeping the car warm but it doesn't turn on even after the car is turned off?

Can be used to keep the interior warm in cold weather. Draws warm air from engine bay into the car.

Edit - from AI search:

AI Overview

The REST (Residual Heat) function on a 2006 BMW 325i (E90) draws warm air from the engine bay and the engine block, using the remaining coolant heat. It works by running an auxiliary water pump to circulate this hot coolant through the heater core, then using the HVAC blower fans to push this warmth into the cabin for 10–15 minutes.

This video explains how to use the REST button to stay warm in your BMW:

Key Details About the REST Function:
Source of Heat: The residual heat stored in the engine's liquid coolant and engine block metals.

Activation: The engine must be off, and it works best when the engine is already at operating temperature.

Conditions: Typically operates when the outside temperature is below 77°F (25°C).
Operation Time: Runs for roughly 10–15 minutes, or until the battery reaches a low voltage threshold.

Function: It is designed to keep the cabin warm during short stops in winter

Great feature. Keeps the HVAC running for a bit to keep your interior warm on cold days if you run into the store for a bit etc. Got deleted on later build e90s.

whyzee125 wrote

Great feature. Keeps the HVAC running for a bit to keep your interior warm on cold days if you run into the store for a bit etc. Got deleted on later build e90s.

Yeah mine must be deleted but so cool that they thought of that even back in 2008!!

greenohawk69 wrote

Can be used to keep the interior warm in cold weather. Draws warm air from engine bay into the car.

No. It uses the residual heat in the cooling system (i.e. hot coolant) heater circuit to run the cabin heating when the engine is turned off. It works because the E90 engine(s) use an electric coolant pump to circulate engine coolant. The REST function circulates hot coolant through the heater core after the engine is turned off and runs the HVAC blower motor to circulate air over the heater core.

OP, the accessory mode of the ignition needs to be on (i.e. engine off) and the cabin temperature set to heat for the REST function to work, and the coolant needs to be hot. Also, if the battery is not sufficiently charged the REST function will not work. It will run about 18 minutes on a cold day and stops once the coolant temperature falls below a set threshold. The owners manual explains how to use the REST function.

I have a LCI model and it didn’t come with REST button. Instead it had a sync button but I bought a REST button off eBay and coded it and it’s working as intended.

lordnikon wrote

I have a LCI model and it didn’t come with REST button. Instead it had a sync button but I bought a REST button off eBay and coded it and it’s working as intended.

Oh wow, I would rather have the sync!!!!

Can sync be coded in? I have the bimmercode app.

BimmerGuyHere wrote

Oh wow, I would rather have the sync!!!!

Can sync be coded in? I have the bimmercode app.

I believe it can; I did it manually but don't remember the coding instructions.

Only tried it 1X in 19.5 years....

greenohawk69 wrote

Can be used to keep the interior warm in cold weather. Draws warm air from engine bay into the car.

Not warm air. It runs the electric water pump to keep circulating hot coolant into the heater core so that it keeps the cabin warm.

BimmerGuyHere wrote

Oh wow, I would rather have the sync!!!!

Can sync be coded in? I have the bimmercode app.

Yes it can! I have it coded in my '11 e91 to rest heat. I did it 15 years ago so I can't tell you how, but I used ProTools. There are tutorials here on how to do it. I think it was actually one of their "one click" coding options.

The irony is that after the first winter with my car I bought an SUV and my wagon hasn't turned a wheel in cold weather since - and then a few years later I started wintering in Florida. Been meaning to code it back to ALL, but it does work very nicely to keep the car warm if you are out and about on cold days.