Occacional Main Warning Light on startup - possible reason?

In your second thing there I don't see any lights on the display or the CM monitor the gas gauge speedometer etc. this is what my 09 has been doing for years but it hasn't done it now for about 7 months. When I get in the car push the brake and hit the button I'm looking at my check engine light and my zero on the speedometer at the same time The minute I let go of that button if I don't see a zero and my check engine light isn't doing right I immediately hit the button again and the car is off. Then upon reapplication of the break and hitting the button again I see my check engine light and the ambers come on and the zeros present I'm good to go. If you want to know this is fact open your door If you don't see the door open red icon you're going to have no display upon pushing the start button I can almost guarantee it. Get out of the car go to the trunk right above the battery is a little plastic 90° piece that holds the battery cover to the inner well liner You can pull that forward push down on it and now throw that piece in the trunk look through that hole and you see your ground battery strap at the frame It's a 10 mm. Loosen that 10 mm and now look at your display and while you move the ground wire a little You hear the arcing noise you'll see the display icon light up because you have the hatch open tighten the ground leave the plastic thing off you may do this again close the hatch open the door you still see the door open light come on sit in the car push the brake push the button you have a display. Run a scan of the car now Do you have the CM monitor lost communication code? I've never had this code on my '09 after resetting the display a few times changing it a few times with known good units from my own stock so on and so forth finally the problem is well gone away for the last eight nine months and a woman's driving the car so if this was going to happen the person who's driving the car right now would have been dead in the water 7 months ago that's just the kind of look this person has.

 

have you checked the oil level and 12v health?

 

here, the auto parts stores will do a load check for free. if that is not available to you, get a digital multimeter and check the voltage at the jump point under the hood first thing in the morning before driving. best to pop the hood the night before so you don't have to open the drivers door which puts a load on the 12v.
then get in and turn on everything possible without making the car ready. high beams, radio, hvac fan, etc.
then measure the voltage every 5 minutes for 15 or 20 minutes to see how it drops.

 

you can try it, but you'll have to interpolate the results since there will be a load on the battery to begin with. you'll never know the resting voltage.

no trouble codes showing with your scanner?

 

The only time I experienced something similar was when the original 12v battery started to fail - replaced in 2014. Guess what? I’ve been running on the same 12v battery ever since - and it’s now 2023…!!!
I expect this to happen to me anytime now - especially as it’s getting much colder in London, UK.
Winter is coming!


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