Dead battery problem
04-25-2024, 08:07 AM
#31
AudiWorld Super User
You did not specify the model year for your car which is always useful.
In your first post you said
I assume you are jump starting using the jump terminals in the front of the car? If so, are you trying to use a battery charger as the jump start means or are you using a second car with a running engine as the source? Your one month without operation on what is presumably a battery that is a few years old likely means that the battery is beyond recovery. On a battery that is beyond recovery, you can leave the charger on it for a week and the battery will not accept any charge.
Based upon your description of what is happening with the lights, I expect that you are attempting all of this with a smaller battery charger. A plain battery charger will certainly not be able to start the engine and a small one may not have enough current capability to operate the trunk release mechanism. In order to attempt to start the engine you would need what is called a jump pack (bigger is better) or arrange for a second car with a running engine to act as the starting source. A large capacity jump pack or a second car should drag your car up to the operating voltage of the source and allow it to start or at the very least open up the trunk. If I knew that this was just a case of a dead / open circuit battery I would say either method would be OK; however, since there might be other problem at play with your car I suggest trying the jump pack. Good jump packs generally have protection in them which deals with dead shorts or polarity reversals. If you use a running car as the jump source and you have a short circuit some place you are going to be in for a very nasty surprise when you connect the jump cables.
In your first post you said
I assume you are jump starting using the jump terminals in the front of the car? If so, are you trying to use a battery charger as the jump start means or are you using a second car with a running engine as the source? Your one month without operation on what is presumably a battery that is a few years old likely means that the battery is beyond recovery. On a battery that is beyond recovery, you can leave the charger on it for a week and the battery will not accept any charge.
Based upon your description of what is happening with the lights, I expect that you are attempting all of this with a smaller battery charger. A plain battery charger will certainly not be able to start the engine and a small one may not have enough current capability to operate the trunk release mechanism. In order to attempt to start the engine you would need what is called a jump pack (bigger is better) or arrange for a second car with a running engine to act as the starting source. A large capacity jump pack or a second car should drag your car up to the operating voltage of the source and allow it to start or at the very least open up the trunk. If I knew that this was just a case of a dead / open circuit battery I would say either method would be OK; however, since there might be other problem at play with your car I suggest trying the jump pack. Good jump packs generally have protection in them which deals with dead shorts or polarity reversals. If you use a running car as the jump source and you have a short circuit some place you are going to be in for a very nasty surprise when you connect the jump cables.
04-25-2024, 09:58 AM
#32
AudiWorld Super User
CD navigation unit in the glove box, that's MMI 2G low (MMI basic plus with CD navigation), PR 8DP+7Q9. So this is a MY08 or MY09. Still, would be the same understanding in this issue for any B8. The 7th/8th characters of the VIN do say 8K, not 8E? The rear seats do not fold down because the car is PR 3ND and not 3NZ, not just because it's a sedan. But if you are 3ND, then you have the emergency release cable 8K5880701 to be found under the seat bench.
04-25-2024, 10:27 AM
#33
AudiWorld Senior Member
A Ctek like charger would definitely not have a start option. I am not familiar with all the start options on larger battery chargers; but, the ones I have seen are more of a start help function. They are limited to supplying about 75 ish amps which will help get the car started if the battery is partially discharged and unable to spin the starter motor quickly. If the battery is completely dead those start assist functions usually don't do the trick. Even the smaller jump packs will struggle with a completely dead battery. The more robust option is jump starting from a running car (or a tow truck); but, can be more dangerous if there is something wrong with the electrical system on the car being started.
Given the parasitic loads on the A4, letting the car sit for a month without operation pretty much guarantees a no start. If the OP wants to do that they need a battery maintainer or an isolating switch on the battery negative terminal to shut everything off while the car is in storage - although that really does not work if they don't have an emergency release on the trunk to get back in to reconnect the battery.
04-25-2024, 11:03 AM
#34
AudiWorld Super User
i would have thought he left a battery charger on it last night just to see.... i would have thought even a 90% dead battery would at least pop the trunk, but ya never know ..
04-25-2024, 12:35 PM
#35
AudiWorld Super User
What voltage is measured at the jump start posts? What resistance is measured at the jump start posts? If you put an intelligent charger / battery assessor on the jump start posts, what does it say about the battery state? If you put a power supply on the jump start posts, do you get at least a 12v reading? If so, it should be enough to let the J393 respond to the rear lid release key fob press. Don't bother trying to turn on ignition unless that power supply is at least a 20A steady state, and you make sure to turn off the climate control system.
04-25-2024, 01:12 PM
#36
AudiWorld Senior Member
In the ancient days where the hood release switch was a switch which operated the solenoid directly, there might have been enough jam left in the battery to operate the release solenoid. However, on the Audi I suspect that the switch probably communicates with the BCM or whatever and the module powers up the solenoid. If the module has 5 volt CMOS logic, even with a low drop out voltage regulator the module probably needs to see a steady supply voltage of a minimum of 7 volts. If the Audi has other parasitic loads dragging down the voltage the module may cease to function. However, as I noted before, there might be other things going on with this car contributing to the problem. My gut reaction would have been that a reasonably sized battery charger should have had enough jam to operate the hood release solenoid and to SMac770's point, if the voltage at the jump start terminal is 12 volts are higher with the battery charger connected I would expect that it should operate the trunk release mechanism.
04-25-2024, 03:53 PM
#37
AudiWorld Super User
The door release is actually connected to the J386 driver's door control module. That then passes a CAN message along to the J393, which then powers the rear lid latch release. This requires both modules to be working and awake. The more direct approach would be to just use the rear lid release button on the key fob. The key fob aerial is connected directly to the J393, and always works regardless of the wake state of the vehicle. But that assumes the J393 is operating.
Wouldn't be a first time if I gets it open to find water all over and fuses blown.
Wouldn't be a first time if I gets it open to find water all over and fuses blown.
04-25-2024, 04:38 PM
#38
AudiWorld Super User
The door release is actually connected to the J386 driver's door control module. That then passes a CAN message along to the J393, which then powers the rear lid latch release. This requires both modules to be working and awake. The more direct approach would be to just use the rear lid release button on the key fob. The key fob aerial is connected directly to the J393, and always works regardless of the wake state of the vehicle. But that assumes the J393 is operating.
Wouldn't be a first time if I gets it open to find water all over and fuses blown.
Wouldn't be a first time if I gets it open to find water all over and fuses blown.
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