AlexA4B8Fan

2013 A5 engine light came on. Ran diagnostics and saw auxilary coolant pump issue (P261A00). This morning I popped the hood to see location of the pump, and dead battery. Down to 5V. Sat a while, got up to 11V, but not enough to start car. Checked again, down to 5.5V. How can voltage move that fast in a battery. I did pull out the OBD Eleven. I am currently charging the 2 year old (fairly new) battery, after disconnecting the positive terminal. I take it that following typical protocol to avoid lost codes is nulll and void at this point, so disconnecting without adding 12V to car system should not be an issue.

So I am quite bad with electrical. I put a resistance meter across terminals that go to battery to check for dead short. It was 5M ohms and some change. No idea what it should be, but not a dead short anyway.

So what would be my next step here. Any advise is greatly appreciated. This all sounds so freaking expensive, and I am not in a position to deal with this sudden expense. Thanks

AlexA4B8Fan

Update: I charged the battery for 20 min, hooked up the Pos terminal, car started right up. Let it run about 15 min. Shut off and checked voltage again after 30 min and at 12.06V. Hmmmm

findalex

15 minutes of idling isn't going to fully recharge a battery. If you haven't changed the battery in about 5 years, it's probably reay to go out. Becoming fully discharged only kills the battery sooner.

If I were you, I'd hook up a dedicated battery charger (maybe with desulfation feature) and let it charge 24 hours. Or there are cheap car battery testers that you can buy to check on the health of the battery.

SMac770

Don't leave the OBDeleven plugged in when you're not using it. It will run down the battery.

I'm pretty sure you should never connect a meter in resistance mode to a powered circuit. The correct way to measure a battery internal resistance would be to compute the resistance due to change in voltage during two different current flows.
https://www.hagerty.com/media/mainte...ng-resistance/
https://batteryuniversity.com/articl...nal-resistance

You have a scan tool, so query some useful electrical system info, block 14 and block 18 and block 19 of the J533 (19-can gateway). 014-1 will be the commanded alternator output voltage, 018-1 will be the measured battery voltage, 019-1 will be the computed battery state of charge. You might also check 001 for the term 30 and term 15 voltages as seen at the J533.

The aux coolant pump, if it's referring to the one that was safety recalled for fire risk due to overheating of the electrical connector, ....

Why let it just sit there idling for 15 min? Put the battery on a proper tester/charger and let the device do its job to completion.
Actually, while the battery is out, do you measure a resistance between the unconnected positive and negative battery harness connections? Won't help determine a problem with semiconductor devices, but if you do measure a reasonably low resistance, you've got something shorting somewhere.

AlexA4B8Fan

Great advise all. SMac, I did check resistance across the wires that attach to the battery when pos was disconnected, and got 5M Ohm. So no short. As mentioned, I did charge the battery up enough to start, only took about 30 min. I have a 10A charger. And yes, the aux coolant pump was coded as being stuck and bad. It needs replacing. Is it covered under the recall?

SMac770

Yeah, the V51 auxiliary coolant pump (the afterrun pump that runs to circulate coolant through the turbo on engine off) was changed for B8.5, and it can clog with debris causing excess current draw which will burn out and melt the connector and set the engine on fire. This was a big deal several years ago when the recall was issued. The pump should be disconnected until it is replaced, and it's a NHTSA safety recall, completely covered (should be).

https://web.audiusa.com/recall/

At the very least, unplug it and look at the state of the plugs, see if they appear melted on the harness or pump.

Next step would be to connect the battery, give it a minute for the modules to wake, then check the voltage drop on all the fuses, see if anything, before the car is even ignition on, is drawing a substantial amount of current. That includes checking the fuses in the ECM box under the hood.

A charger alone is only half good; would be better if you had a load tester also to see if the battery is storing a reasonable charge quantity. For example, if you log battery voltage while cranking the engine, does the voltage stay above 10.0V or drop below. It should not drop below 10s to start the engine.

AlexA4B8Fan

Thank you soooo much and Thank God for forums like this. I am quite handy, once I know where to look. So you say check/and or remove the connector that has been known to short. That certainly can explain my sudden dead battery that is new. Now, I just have to find out how to locate this pump......

AlexA4B8Fan

....so I looked at the pump, I know it's the correct one becasue of followed the metal coolant line coming from passenger side turbo location, crosses over to the driver side then connects to a rubber hose tha that routes downward to the pump located right below and slightly rearward of the throttle body. And I see the connector location molded to the pump, but there is no wire attached to it. I looked everywhere within about a 1 ft radius to see if it moved away, and there is not spare wire/connector anywhere near the pump. Huh? What do you think is going on there

SMac770

https://static.nhtsa.gov/odi/rcl/201...8V229-9666.pdf
page 10, 11, and 15

Did you check your VIN on the Audi site I linked to confirm the status of any recalls for your VIN? Had the disconnect been performed, had the replacement been performed, had nothing been done.

page 19, it looks like if the disconnect was done, then the harness plug is tied up somewhere.

The V51 pump gets 12v from the fuse 7 in the ECM box, along with a number of other devices (like the N422 coolant shutoff valve and the N144 and N145 motor mount solenoids). I'd test the voltage drop across that fuse to see if there's an appreciable current flow even with the ignition off or with the ignition on but engine off. That fuse only gets 12v when the J271 Motronic relay is activated by the ECM. So no only should there be no voltage drop with ignition off, there shouldn't be voltage at all. With ignition off, testing resistance from the fuse to chassis might be something to try.