2010 A4, 2.0T Quattro

Any advice on where to start?

My code reader shows a low voltage condition on every car component EXCEPT the ECM. I tested the battery, which is less than a year old, and see 11.77 Volts. Same reading at the positive terminal in the engine compartment. When I try to start the car, there are severe misfires (the code reader says on Cyl 1 & 4) and it stalls quickly, never even getting a chance to idle. There was a warning sign. Prior to its current condition, the car was idling roughly but was completely smooth on acceleration and at speed. On visual inspection I can't see anything obvious. I would think if it was a short a fuse would have blown.

 

On a resting battery at 20C, a voltage of 11.77 volts would indicate a charge level of around 10% for an AGM battery or around 20% if you have a flooded cell battery. So, that would suggest that your charging system is probably not functioning. However, in order to test the charging system you really need to have the engine running. With the engine running the voltage at the battery terminals should be higher than 14.2 volts. If you can get the car running test the battery voltage. If it is below 14.2 volts you likely have a charging system problem of some kind which could be the alternator and or regulator or it could be bad electrical connections.

Depending on how long your battery has been in this discharged condition, it may be beyond recovery. At some point, discharged batteries will not accept charge. You may need to take the battery to a specialist to determine whether it is salvageable. If you can recharge the battery or purchase a new one, you should be able to install it and start the car which would then allow you to do a running voltage test. If the running voltage is not above 14.2 volts then you have a charging system problem and you need to stop the engine and diagnose the charging system before you kill the battery again.

If your charging system is dead, the battery in its current state of charge will likely not allow engine operation. With a non functioning charging system if you do manage to get the engine to start the battery voltage will likely drop way below 11.77 volts which will lead to erratic behaviour or non operation of electronic components. Both ignition coils and injectors are sensitive to supply voltage. The ECU will have dwell adjustment curves and injector offset curves for reduced voltages; but, once the voltage drops off the edge of the adjustment curve you enter in to the land of erratic operation.

 

Is that also true if I have an external charging source? I used jumper cables to try and start the car (yes the battery did discharge) but I got the same misfiring problem and immediate stall. Also note that its a manual transmission.

 

rough idle can be a number of things, such as PCV or plugs or coils or injectors or fuel pump, etc. But if it was only rough at idle and ran under load fine, probably PCV. But PCV doesn't normally cause a full stall. You need to scan for DTCs and see what comes up.

Have you run the the battery down trying to restart the engine? Pull the battery and put it on a charger to restore it's state first. If the engine is starting, but not starting well, there's no assurance the alternator output is stable and able to take over running the vehicle from the battery.

 

Did you try to jump start the car from another running vehicle? Unless you have a serious wiring problem on the A4, the other car should have been able to maintain the voltage on the A4 allowing for operation - if the wiring is not messed up. If that external source was a portable jump pack, it is impossible to say without knowing the capacity of the jump pack and the state of charge of the jump pack. A small jump pack may not be able to maintain a stable voltage on the A4 if the A4's charging system is dead.

If you were using another running vehicle to do the jump start and the A4 would not run while connected to that other vehicle I think you have a fairly significant vehicle electric problem.

As a matter of interest, since your current battery is less than 1 year old, when the battery was installed was the correct adaptation process for the battery carried out? If the charging controls were not reset for the new battery you may have cooked it by over charging it.

 

Never knew that it was necessary to do an adaptation process for a new battery. I do have a code scanner for Audi's that lets me customize settings. I may look into that at some point. For now, however, I did have it jumped with a running car. Since no fuses are blown, perhaps I can try and trace the wiring from the battery to respective fuse blocks to see if there is a short.

 

The car systems run off the battery connection. Engine off, the battery runs the car. Engine on, the alternator runs the car, but the alternator voltage has to make it to the battery positive post before it can pass to the car systems. All the fuse blocks run off the C and D posts of the fuse panel A (the block on the battery positive post).

Excessive voltage drop across a wiring path will be near zero when the current is near zero. So the voltage across the battery posts and the across the jump start posts and across the alternator (B+ output post to housing) should all be the same engine off. If they are not about the same engine running, then you know you have a problem with the charging system wiring path.

If you are seeing lower voltage at a fuse than at the battery positive, then there's an issue in the wire path from the battery to the fuse. The fuse row might be a single connection or each fuse might be a separate connection.



U6 and 615 are the jump start posts.




You'd need to be more specific about which fuses are seeing significantly below (more than a few tenths) battery measured voltage to speculate any possible cause. There's also the fuse row in the ECM box.

The battery adaptation should be done on a battery change event, after resetting the date/time. If you can't do the adaptation, the battery should only be replaced with the same kind/size. But it's not going to make the vehicle stop working altogether.

 

So, with using a running car as a jump source, your engine would not run continuously? Did your car run while connected to the jump source and die after disconnection or did it fail to continue running even while connected to the jumps source? Where did you attempt to jump start the car, at the jump start terminal or at the battery terminals?

If you jump started using the jump start terminal and the starter motor was spinning at its normal speed, then a bad connection from TV22 to the battery could result in low voltage at the battery and the rest of the car. If the starter motor was slow to turn over, a bad connection between the jumps start terminal and the starter motor may be the problem. As per the diagram provided by SMac770, either of those connection problems will affect the charging of the battery and can result in low voltage in the vehicle electric system even if the alternator is cranking its little heart out. If you can get the engine to run, measuring the voltage at B+ on the alternator, 30 on the starter motor, the jump start terminal (TV22) and then the battery + terminal may give you a clue as to where the problem is. Don't bother with this test if the car is not running.

I would not start by looking for a short circuit. Short circuits are usually characterized by no voltage, not low voltage. Bad connections are the more likely issue. I would start by checking all the connections in that circuit that extends from the alternator B+ terminal all the way back to the battery + terminal. Bad connections at the fuses on the A fuse panel can cause low voltages in different areas of the car; but, should not affect the ability to charge the battery if the alternator is functioning. Rough handling of the A fuse panel when replacing the battery can cause damage to the connections / fuses. Make sure that you check the chassis ground for the battery - terminal. Corrosion on that connection will cause problems.

Failure to adapt the charging system to your new battery is probably not the cause of your present problem, although your 1 year old battery may now be suffering from premature ageing and due for replacement. Audi appears to alter the charging voltage (upwards) as the battery ages. The adaptation process resets the voltage to something that is more appropriate for a new battery. Failure to reset the voltage will likely result in overcharging of the battery shortening its life. AGM batteries have a slightly different ideal charge voltage than flooded cell batteries which is reflected when you enter the battery type. However, for over a decade people have been stuffing AGM batteries into cars that were originally equipped with flooded cell batteries without any modifications to the charging system and without any material issues. Can't comment on the effect of installing a flooded cell battery into a car originally set up for an AGM battery.

 

For some background, this is my teenage sons car. I'm desperate to get it running since he is now using my S4, a recipe for disaster.

The starter was replaced about three months ago. It cranks effortlessly. With a running car as a jump source (the aforementioned S4), it does not run continuously and its connected to the jump source not the battery. Note that its the same behavior even without a jump source. The engine sputters violently and then stalls. I need to try to find some time away from my normal job to follow these suggestions. I appreciate all the feedback. Also, as an experiment, I compared the voltage of the battery with and without it being connected and there is very little difference (11.92 vs 11.94). The jump terminal measures 11.90.

 

You need to separate if you're working a charging system issue or an engine issue. As noted in the pic, the car electronics run from the battery posts, not the alternator "posts". And if the battery reads under 12v static, then it's too low charged anyway. Pull it out, put it on a proper charger for the type that it is (AGM vs wet flood), get it back to 100% SoC. Reinstall it, note the voltage, check for that voltage on all the term 30 fuses. Though the ones of interest to the engine operation are in the ECM box. If all the fuses look good, the battery alone should be enough to start the engine and run it idling for a minute. If it's dying as soon as it starts, you have an engine issue. Do you not have VCDS?