Greetings I'm new to the site. 

I recently replaced the battery of my Legacy 2.5 GX today, the battery had died over the winter and there were many signs the battery was running low, including power windows making the headlights dim and the alarm going of at random occasions with no flashing lights. Into December and the battery finally died and I did not want to replace it until the spring when I was planning to reinsure the vehicle. The only work i've had done to the car was changing the coil pack and spark plugs. I have owned it for 1 year and only done 2000 miles on it. Current mileage: 130000 miles

However after taking the car for a brief test drive after adding the new battery the air suspension sank and indicated a problem by flashing the HEIGHT HI light in quick succession, I stopped the car to check and restarted it to try to see if I could raise the suspension as normal using the button but it wouldn't rise. This problem has confused me because the air suspension was working fine before the battery died and I left it on over the 4 months were the car just sat in the drive and didn't sink like it normally does over long periods of time. Is this problem related to the electrics? I really cannot afford to fork out any more large amounts of money for this machine as its cost me a bomb already to insure as 19 year old in the UK. 

Thanks in Advance

Have you checked the fuses ? Could have blown one when the battery was swapped ?

Are there any error codes availbe to read on the diagnostics ?

Don't know much about air suspension systems so sorry if you've already investigated these

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Not sure about subarus but some manufacturers require an initialisation procedure for air suspension systems after a battery replacement. If the car has been sitting a while, there’s also a chance one/some of the height sensors have seized, giving a false/abnormal reading of vehicle height (this will normally only drop the corner with the faulty sensor though).

Thanks for the responses guys, I washed it recently and after restarting the system it went back up again with no trouble, perhaps it had gotten stuck from dirt after the break in which it was off the road. I will bear in mind the responses in future though, the air suspension is the thing I'm most paranoid about on the car.