obdII reader draining battery?
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Audiworld Junior Member
Joined: Sep 2017
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From: NB, Canada
Parasitic drain?
So I have had my 2003 A4 1.8tqm for about half a year now, and havent had any major problems considering what I paid for it. The car came with quite an old battery and as expected it called it quits a few months after I got it, which I ended up replacing with a new one of slightly higher CCA's. All was well and the battery voltage was over 14V while the engine was running since I replaced the battery, and the last time I checked the voltage was just a few days ago. Long story short, I drove the car day-before yesterday and it started just as quick as it ever had, but this morning was a different story. The battery charge was so low the automatic locks didnt even work, and I had to open the door manually. I checked the battery voltage through the obd reader and it read 6.6 volts which is basically nothing.
It wasent that cold outside, and the only thing different now is I had the obd reader plugged in for the past few days, so I'm trying to figure out weather the obd reader caused a parasitic draw that drained the battery over the weekend? I checked if I left the headlights or any interior lights on, but coudnt find anything that would drain the battery. The last time the battery died was in an equally sudden and mysterious manner, but I chocked that one up to the battery being old.
It wasent that cold outside, and the only thing different now is I had the obd reader plugged in for the past few days, so I'm trying to figure out weather the obd reader caused a parasitic draw that drained the battery over the weekend? I checked if I left the headlights or any interior lights on, but coudnt find anything that would drain the battery. The last time the battery died was in an equally sudden and mysterious manner, but I chocked that one up to the battery being old.
Last edited by LordKarnage17; Mar 29, 2018 at 04:48 PM.
Thread Starter
Audiworld Junior Member
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From: NB, Canada
It seemed a bit lighter than I remember when I took it out of the car, but there wasent any residue in the battery compartment, and I feel like fluid draining in just a few months is unusual. Either way, I got it from Walmart with some sort of warranty, so I dropped it off there and they're seeing weather it can be charged up or needs to be replaced.
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From: San Diego, CA
An OBDII dongle will drain your battery, but shouldn't have caused what you're seeing. I suspect that your alternator may be bad, and that can both drain and damage the battery. Best to get it checked out before wasting more time and money on batteries.
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Audiworld Junior Member
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From: NB, Canada
What would be the best way of testing the alternator? I figured having a voltage of over 14v at idle was within spec. Apparently the guys looking at the battery said it was ok after being charged, so I'll keep an eye on the voltages while driving.
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From: San Diego, CA
I've always had the dealer test it when they replace the battery, and I don't know what they do. When my alternator died in my Lexus and the battery lost its charge, it basically shut everything down in the car except for the engine while I was driving (dash went dark, steering and brake assist was gone, etc.), and you definitely don't want that happening to you in the middle of nowhere. Luckily, I was in a parking deck about to pull into a space, and I was able to push my car the rest of the way and get it towed to the shop. It freaked me out.
Thread Starter
Audiworld Junior Member
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From: NB, Canada
I've always had the dealer test it when they replace the battery, and I don't know what they do. When my alternator died in my Lexus and the battery lost its charge, it basically shut everything down in the car except for the engine while I was driving (dash went dark, steering and brake assist was gone, etc.), and you definitely don't want that happening to you in the middle of nowhere. Luckily, I was in a parking deck about to pull into a space, and I was able to push my car the rest of the way and get it towed to the shop. It freaked me out.
One think I did notice is regardless of weather the engine is on or off trying to raise the windows when they're already closed, dims the headlights just a bit. That does seem to lead towards a charge issue, just not to the extent you've described.
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Thread Starter
Audiworld Junior Member
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From: NB, Canada
Ok the plot thickens. I had the obd reader disconnected, and the battery died again today. Drove it to town, parked it for an hour and a half, came back to a battery at 8V which wasent anywhere near being able to start the car.
I leave it parked there, and come back later in a buddy's car with a pair of jumper cables, only to find out somehow the voltage was back up enough for a single crank (it was low but enough to crank over the engine), so I'm very confused.
Every time I've checked the battery voltage while the engine is on its been near or above 14V so the only other option is some sort of parasitic draw, but I'm hard pressed to think of any sort of parasitic draw that can drain the battery that much over the span of just an hour or 2.
I leave it parked there, and come back later in a buddy's car with a pair of jumper cables, only to find out somehow the voltage was back up enough for a single crank (it was low but enough to crank over the engine), so I'm very confused.
Every time I've checked the battery voltage while the engine is on its been near or above 14V so the only other option is some sort of parasitic draw, but I'm hard pressed to think of any sort of parasitic draw that can drain the battery that much over the span of just an hour or 2.
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That is one heck of a parasitic draw. Possilbe, but only likely if your brake lights aren't going off
So, I will go back to my original questions.
1. Have you checked the electrolyte levels in the battery?
2. How much over 14V are you getting out of your alternator? I ask because perhaps your voltage regulator has failed, the voltage is too high, and you have cooked your battery.
What is the voltage of your battery after you charge it with your engine off?
So, I will go back to my original questions.
1. Have you checked the electrolyte levels in the battery?
2. How much over 14V are you getting out of your alternator? I ask because perhaps your voltage regulator has failed, the voltage is too high, and you have cooked your battery.
What is the voltage of your battery after you charge it with your engine off?
Thread Starter
Audiworld Junior Member
Joined: Sep 2017
Posts: 44
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From: NB, Canada
That is one heck of a parasitic draw. Possilbe, but only likely if your brake lights aren't going off
So, I will go back to my original questions.
1. Have you checked the electrolyte levels in the battery?
2. How much over 14V are you getting out of your alternator? I ask because perhaps your voltage regulator has failed, the voltage is too high, and you have cooked your battery.
What is the voltage of your battery after you charge it with your engine off?
So, I will go back to my original questions.
1. Have you checked the electrolyte levels in the battery?
2. How much over 14V are you getting out of your alternator? I ask because perhaps your voltage regulator has failed, the voltage is too high, and you have cooked your battery.
What is the voltage of your battery after you charge it with your engine off?
Depending on how discharged the battery was the voltage while the engine was on hovered between 3.6v and 14.2v. After turning off the engine it dropped gradually to around 12.5v. That all seems pretty normal to me, but I'm by no means an expert on this and have only started researching this stuff after these recent issues.