I don't have heated seats in my Redline Ute, the driver's side doesn't even come with the electrics to move the seat back and forth, Holden in their cheapness just provided a couple of old milk crates and a fluffy cushion.
But I do have them in my Euros and they reach maximum temperature within a couple of minutes then slowly reduce in temperature until they turn themselves off.
There is a gauge on the dash where you can see the temperature for both front seats and see it reduce.
The thinking behind it is you get into a cold car and need the seats to warm you quickly, once warm they can be turned off as the body temperature of your bum will keep you warm.
If you're not happy with that you can always hit the button to switch them back on.
In saying that I find mine a bit too warm and of no real use in the warmer climates, I'd rather ventilated seats.
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Do your ute seats 'breakover' like proper ute seats? To get access behind them?
I'm not a real fan of the seats in the Magnum. They are fully electric, recline, up and down, tilt and fore and aft.
The broadcast sheets state they are memory seats, but the ute BCM doesn't have that function.
I think they're basically sedan seats, the seat backs barely move forward. Makes it awkward to access the battery and wheel change gear.
The only good point about the seats are the heaters, although they are slow to heat up. Very handy here this time of the year.
Not as good as the Astra though. I used to finish night shift at 6am, start the car, turn on the seat heater, then scrape the ice off the front and rear screens.. My bum would be warm leaving the car park, and I'd turn them off within a couple of kilometers.