Car loses all electrics when turning key

[GregS4]

Hi all,

I have a B6 S4 Manual. I replaced the battery around 6 months ago. But recently the car was taking a little longer to start until the other day when it didn't start at all.

When trying to start it now, I put the key in turn it once and all the electrics come on fine, and all light up. But when I try turn the key again to start the car just shuts down and all the electrics go off.

The only way to get the electrics back on is to wait a few hours or disconnect the battery and re connect it, then all the electrics work again.

I'm in need of the car as soon as possible.

Thanks in advance,

Greg

[Cinna696]

Check your battery voltage with a multimeter, sounds like it's dead. Since it's only 6months old you should have your charging system checked and/or the car for a drain on the battery.


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[PetrolDave]

Sounds like the battery has gone high impedance so when you place a heavy load on it (as when trying to start) the terminal voltage drops very low.

Since the battery is only 6 months old I'd start by checking the volatge when the engine is running and the alternator should be charging - it could be too low or too high to cause the battery to fail.

[GregS4]

Sounds like the battery has gone high impedance so when you place a heavy load on it (as when trying to start) the terminal voltage drops very low.

Since the battery is only 6 months old I'd start by checking the volatge when the engine is running and the alternator should be charging - it could be too low or too high to cause the battery to fail.

Thanks for replying.

I'm unable to start the car to check? Any ideas?

I've got a battery pack to jump it, that fails as it just cuts out, and so does jump leads from my other car... Both just cut out all the electrics when trying to start it.

[PetrolDave]

I've got a battery pack to jump it, that fails as it just cuts out, and so does jump leads from my other car... Both just cut out all the electrics when trying to start it.

Isn't there a relay that cuts power to non-essential electrics when starting? I wonder if you've got a relay problem, there are some in the area under the ECU where water often accumulates and that can "kill" the relays.

[GregS4]

Isn't there a relay that cuts power to non-essential electrics when starting? I wonder if you've got a relay problem, there are some in the area under the ECU where water often accumulates and that can "kill" the relays.

Well we have had a lot of rain this week in Cumbria!!

Are they actually underneath the ecu box? I've been struggling to get to the last screw to remove the top of the ecu lid off.

[getslideways]

put a battery charger on it for a bit, or how long are you putting the jump leads on for? It may need to sit that way for a bit while raising the rpm of the other car. It may not immediately work. Same with a jump pack, especially if its been sitting around for a while in the cold too.

How long was the car sitting before you tried starting it (how much time since the last time you drove it). Also, lots of short trips wont give the car much time to replenish its battery.

Cold weather cuts a battery's ability drastically.

Also check and clean your battery cables as weak connections and weak grounds can show the same results as a low battery, where low draw electronics work fine, but when a high amp draw like a starter is engaged it cant keep up, and pulls energy from everything else it can. Electricity is sort of like water, it needs to "flow" so any kink in the electric circuit (weak connection) limits the amount of power that can be delivered when asked.

Pickup a multimeter, they are essential for diagnosing electrical problems.

[VinnysS4]

put a battery charger on it for a bit, or how long are you putting the jump leads on for? It may need to sit that way for a bit while raising the rpm of the other car. It may not immediately work. Same with a jump pack, especially if its been sitting around for a while in the cold too.

How long was the car sitting before you tried starting it (how much time since the last time you drove it). Also, lots of short trips wont give the car much time to replenish its battery.

Cold weather cuts a battery's ability drastically.

Also check and clean your battery cables as weak connections and weak grounds can show the same results as a low battery, where low draw electronics work fine, but when a high amp draw like a starter is engaged it cant keep up, and pulls energy from everything else it can. Electricity is sort of like water, it needs to "flow" so any kink in the electric circuit (weak connection) limits the amount of power that can be delivered when asked.

Pickup a multimeter, they are essential for diagnosing electrical problems.

What he said...
Absolutely get a multimeter. Harbor freight has cheapo ones for like 5 dollars. They suck but it will tell you if your alternator is providing the correct voltage (after you get it started) and they will tell you your batteries resting voltage.(you could also get a battery/alternator load tester as they arent that expensive either(autozone will test it for free) From what you describe, it sounds like it could be either a loose or corroded ground wire or maybe just a bad battery. Throw the battery on a charger and after it is charged up, check to see if you have any large drains in your system(basically hook up a test light or your brand new cheap harbor freight multimeter inbetween the battery cable and the battery and start pulling fuses. when the light goes out or the multimeter drops down, you will have narrowed your search) If it only gets better after disconnecting/reconnecting the battery...then i'd bet it is battery related

[IslandHydro]

Sounds like there's a connection problem somewhere. Most likely either at one of your battery posts, or at the grounding point for the battery to the frame. Everything works fine until you try and pull large current (starter) and then it opens up. Try putting a voltmeter on the actual posts of the battery (not the connection to the cables) and see if voltage holds while you try to start. If it does then start measuring across the various connections to see where the voltage drop is. Another really fast way to do this is pour a bit of water on both posts, and on the ground to the frame. The offending connection will steam when you try to start it.

[QIKRNU]

OK; not my thoughts, those of my ME/racer brother.

Two thoughts come to my alleged mind.

1) The high resistance at the offending connection will produce a lot of local heat with high current flow which will produce the telltale steam. So in that sense the concept should work.
2) Water in the connection could provide adequate electrical conduction to mask the issue. Ergo, solution is to douse the engine bay with water every time you want to start the vehicle. Caution- there may be unwanted side effects to this procedure. Side effects may include weak spark, no spark, water in the intake tract, engine fire, and explosion. Consult your mechanic before using this procedure.
3) In the time it takes to drag out the meter one could loosen the battery terminal connections, twist the connection parts to break up the corrosion without losing electrical contact (no need to reset the clock and reprogram the radio, both PITA jobs), tighten them back up and try it. If it works you can ignore the root cause until the corrosion rebuilds. Probably a few months during which time you will have forgotten the procedure and have to go back to the internet. Eventually the battery terminals and connectors will need to be cleaned and if you are lucky this will coincide with having to replace the battery and you can get a twofer


OK so that’s three thoughts. But you gotta cut me some slack, I left my calculator in the other room. Besides I’m an engineer and I do scope creep.



[GregS4]

What he said...
Absolutely get a multimeter. Harbor freight has cheapo ones for like 5 dollars. They suck but it will tell you if your alternator is providing the correct voltage (after you get it started) and they will tell you your batteries resting voltage.(you could also get a battery/alternator load tester as they arent that expensive either(autozone will test it for free) From what you describe, it sounds like it could be either a loose or corroded ground wire or maybe just a bad battery. Throw the battery on a charger and after it is charged up, check to see if you have any large drains in your system(basically hook up a test light or your brand new cheap harbor freight multimeter inbetween the battery cable and the battery and start pulling fuses. when the light goes out or the multimeter drops down, you will have narrowed your search) If it only gets better after disconnecting/reconnecting the battery...then i'd bet it is battery related

Thanks,

My friend (old audi technician) seems to think its a earthing issue. I've checked the main one from the battery, and cleaned all the contacts.

I've also tried to jump it again today but had no electrics at all. Even with both jump leads and 2 separate jump packs plugged on.

Just to rub salt in the wound I broke my Metatarsal in my foot last night so even when I get it going I won't be able to drive it for a while.

Reading from above, yeah I don't actually drive the car far too work and when I'm off shift very rarely drive it further than 10 miles a couple of days a week. I know, I know, it isn't good for the car!

So mainly the question is which earthing connections should I check? I have had an intermittent Centre brake light error recently!

[VinnysS4]

Well if it is a connection issue, like a ground/earthing issue, you will need to trace the battery cables.(both positive and negative) The Negative cable goes right from the battery to the Body of the car. It is like 12 inches long. The Positive cable goes two ways. One cable goes down to the starter/alternator and the other cable goes over near the ecm/fuse box. I'm not sure where the frame to engine ground wire is located at, but that could always be the issue. If you had external power hooked up to the car and it still had no juice, i would be willing to bet that it is a corroded/loose connector somewhere in the cables. Copper can corrode over time with the introduction of minerals. Take your 5 dollar multimeter you went and bought after reading here (wink wink) and set it to the OHM setting. Put one lead on the negative battery post (not the cable) and the other one anywhere on the frame/body/engine. What does it say? If it is much more than 0 ohms, you have resistance somewhere in the grounding system(corrosion). now turn it to the continuity test and do the same thing. if it doesn't read continuity, then there is an open ground. Do these tests with the positive battery cables as well(one on the back of the alternator, as much of a pita it is, and do it on the other positive cable and the fuse block.