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Discussion Starter · #1 ·
Hello. I bought this car second-hand in 2017. Mileage now 40K miles. Nice car and easy to drive. No problems except last December the Auto Transmission red warning light came on when starting from cold, but I drove it (a short 10 mile run) and the gearbox worked ok. The warning light came on (only when starting up, ie not during a drive) randomly a few times over a week or so then all ok until this past weekend when the warning light came on again when I started the car. Any thoughts? What sensor would trigger that warning? I should add that it's a Citigo so I hope you don't mind me posting here but no similar Citigo forum that I can find. We also have a Mii Manual in our family. Great cars!
 

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Not sure, but it could be a failing battery.... How old is it?
It may well start the car, but if a little low on volts, I believe the electronics detect this, as the solenoids working the box need some fairly big pulses of energy to do the shifts.
 

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Discussion Starter · #3 ·
Thanks. That's a good idea. The battery is only 2-3 years old, but the car is not getting many runs lately and those runs are all short. Also, back in December, due to covid the car was getting few outings so would have had lowish voltage too. I'll put the battery on charge and see what happens when I next switch on the ignition.
 

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Discussion Starter · #4 ·
I put the car on a smart battery charger and it took longer than expected to fully charge so the battery was more depleted than I thought. After the full charge, I'm pleased to report the warning light did not illuminate again when I switched on the ignition. I need to use the car tomorrow so hope that problem is now solved. Thanks to Freemansteve for his advice.
 

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It's surprising on modern cars how often something electronic goes flaky when the battery is a little low!
In the olden days, you'd know you'd got a low battery by lack of starting at all!

Really, today, all critical car electronics should have 12V up-down DC-DC converters! Very cheap. It would mean that even if your battery dropped below 12V (as they can) then the electronics stay at 12V.
 

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A different make and model but I’ve heard of similar issues with Fiat & Alfa automated manual gearboxes, basically 12v seems to be the bottom threshold.

If the car is garaged or parked close to the house or garage leaving a smart charger plugged in regularly would benefit you both from preventing spurious alarm lights and prolonging the life of the battery. Another option would be a small solar charger, on an Up! it needs hardwiring though as the 12v socket is isolated when the ignition is off. Another key point is not forgetting to disconnect a charger before getting in the car and driving off… saves a great deal of embarrassment.

One thing that is key is keeping the voltage above 11.6v where sulphation begins to occur, basically sulphates form on the plates of the battery, eventually this falls off, builds up at the bottom of the plates, the plates are longer freely suspended in the electrolyte and the performance of the battery begins to reduce.
 
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