Denis_E55

Last night I installed my 77FSP, flashed my tune and went to start my car, battery was dead. I jumped it and my aux battery was low because the door was opened and fan was running while I was using the EuroFlash software, drove the car and the "convenience" functions became available, the only problem I have now is AC OFF is displayed. I had a leak in a line that a shop fixed and recharged my system so I think it's not the system low or bad. Can a low battery cause it to not turn on?

Hulk

When flashing always have a charger attached to the battery or unplug the fan so the battery doesn't drain. Are you sure convenience functions are back because these cars tend to come back and then gone again, how old is the aux battery?

biggking

Yes I've had this issue before, dead rear main battery. Charge them both and remember next time you 'flash' or use any scan tool on your vehicle to put it on a trickle charger/battery tender so that you don't accidentally 'brick' your ECU if the power shuts off.

Yacht Master

Just run the A/C diagnostics and post the readings 1-7.
Did you plug in the air quality sensor you were asking about in that other thread?
Flashing a tune with a low battery is asking for problems.
FWIW I replace any battery that has been dead once, they never really fully recover, and these cars are so electrical complex the risk of damage to the countless modules due to low voltage is extremely high.

RAWE55

Next time you flash, just pop the hood and reach down and unplug the wiring harness to the fan. Takes literally 5 seconds and will save you a head ache and the fear of your battery running out while reflashing. If this happens it can corrupt your ecu and you wont be able to start or run your car till you send in the ecu to your tuner.

Denis_E55

@YachtMaster I did plug in that sensor the day you guys helped me figure out what it was, AC worked after that without a problem.


The AUX battery is only about 2 weeks old, I replaced it because I was getting the convenience function error, the error went away last night after about 5 minutes of driving. I didn't flash the car with a low battery because my rear battery is good. The flash did take longer then expected but it did complete. The fan ran the whole tim (didn't know it was ok to unplug) and the door was cracked open so I could have my laptop plugged into the charger.

Denroll

Anything that draws current from the battery while the reflash is happening makes it take longer. While on a battery charger, I flashed once with the radiator fan plugged in and it took a long time. The next reflash, I unplugged the fan and it took like 1/4th the time. Turn off the climate fan, radio, lights, and unplug the fan next time and see how much faster it is.

Denis_E55

If I did the A/C diagnostic test correctly this is what I came up with...


00=35
01=33
03=28
04=25
05=33
06=82
07=07
08=30


Looks like I skipped over 02, hopefully its not an important number. The car starts and drives fine now, no warning/error lights. Should I keep driving to see if the AC will kick back on or do I need to go to the dealership and have them turn it on?

Yacht Master

#7 is pressure in bar, so you still have a charge, and the compressor should come on when the car is started. The other numbers look to be as expected.
If the compressor dose not come on when the car is started then run the test for fault codes and that will tell you what is preventing the system from working.

Denis_E55

Can i run the fault test without any tools or do I need the STAR tool to do so?

Yacht Master

So the compressor clutch is not engaging, check for voltage to the clutch.
If no voltage then, STAR scan for error /fault codes.
Now did the AC work before the flash then not work after the flash?

Denis_E55

Yep it worked. I talked to Shardul and a shop here they said the battery might have dropped low and the system disabled all the "functions" that aren't needed for driving. I don't have the STAR tool yet and aren't too sure how to check voltage to the compressor. I will drive it for a day or two more and see if it kicks on, if nothing most likely pull the trigger and buy the STAR tool.

Yacht Master

You might try a hard reset, that would be disconnecting the main battery over night (12 hours) and recharging that main (rear start battery) while it is disconnected from the car.
Check all your fuses in trunk, under hood.
Now here comes the public service announcement/broken record, low voltage kills, always make sure your battery is fully charged, and when you get an in dash warrning you do 100% have a problem that needs attention. Low voltage kills. Jump starting these cars can cause electrical dammage too, but if you heed the in dash warrning you chance of needing a jump start diminish greatly. FWIW even a new battery that has been dead once, I will replace and that replacement will be purchased dry and be filled and charged (4 hours) in front of my eyes.