Intermittent electrical power loss.

[Laurie61]

Hi all, my 13 plate superb is doing strange things. The car will go dead after switching off the engine. Up to now if it is left for a few minutes it will spring back to life, the battery is the original but is charged and starts the car without a problem. I have checked the battery terminals and they are fine with leads securely fitted to the battery post's.  The car will run OK when started and the engine does not cut out in use. 

 

Anybody experience something similar or know what it might be ?  

[superbdreams]

possibly a faulty ignition switch. do all the warning lights come on after it springs to life?

(air bag, abs)

[Laurie61]

5 hours ago, superbdreams said:

possibly a faulty ignition switch. do all the warning lights come on after it springs to life?

(air bag, abs)

 

Yes, there are warning lights on for steering Ect after power comes back on, the clock is also reset. I have booked it in at my regular Skoda dealer. I will point them at a possible ignition switch fault when I drop the car in.

 

When there is a fix sorted I will update this thread.

 

Thanks for the reply .  

[PipH]

If the clock is going off I think it must be something more fundamental, like an intermittent problem with the engine bay fuse box.

 

" The car will go dead after switching off the engine " 

It sounds like the alternator is keeping everything powered up while the engine is running.

But without a wiring diagram I can't help further.

 

You could try tapping the fuse box when it's next " dead " & see if power is restored.

[Laurie61]

1 hour ago, PipH said:

If the clock is going off I think it must be something more fundamental, like an intermittent problem with the engine bay fuse box.

 

" The car will go dead after switching off the engine " 

It sounds like the alternator is keeping everything powered up while the engine is running.

But without a wiring diagram I can't help further.

 

You could try tapping the fuse box when it's next " dead " & see if power is restored.

 

My initial thought was that the problem is close to the mains supply or distribution, which is why I looked at the battery terminals. What is harder to fathom is why it comes back to life without moving or touching the car.

 

It goes completely dead and then springs back to life without any input from me.  

 

I guess something could be getting hot, a partial short, which causes a power break and then cools and the connection is re-made?

 

Not as I have detected any sign of hot/burning electrical contacts. 

[chimaera]

If absolutely every electrical component in the car goes dead when this happens, the first thing I'd check is the condition of the main earth connection to the battery: follow the negative lead back to its earth point and make sure that's clean and secure.

 

After that you're into going through fuses and relays to see if any are dead/dying. Confirm if any electrical circuits remain functional when this happens: it'll help narrow down the source of the problem.

[3T51704x4]

If what chimaera is OK, look at the Terminal 15 and X contact relays on J519, swap them over as temp check to see if it still does it.

Check volt drop across battery terminal post and the clamp and get someone to crank the engine. this will show up a poor connection between the battery post and the clamp. You can also test the body and engine earth the same way.

One multimeter lead on battery centre post then the other to the engine block or head. If when it is cranked the volt drop is above 0.2V (I've seen an 8V drop on engine earth) you have a bad cable, poor (corroded) connection or broken wire within the PVC. This is a quick test to see if you have a poor connection without wasting time cleaning connections which are sound.

You can do the same to the chassis from the battery negative post. There are two different main earth circuits, body and engine earth. Use these tests for fundamental loss of battery power.

Go from battery positive centre of post to starter main battery terminal (30) to test starter feed (had this been your issue but it is not)

Batt pos to SB fusebox input to check for volt drop.

Batt pos to SC fusebox input from battery.

Batt pos to J519 input etc etc.

Do it in a methodical manor to speed your diagnosis.

As it is intermittent, you need to do these tests at the time you experience the issue which is why these sorts of events are the most challenging to track down.

VCDS scan could also help narrow down your issue like term 15 relay or X relief relay open circuit sporadic etc.

Edited 9 August, 2019 by 3T51704x4

[3T51704x4]

The reason for doing volt drop testing with the consumer running in the circuit is to identify poor connections and broken strands in wires. 

You can have 12V when measuring a circuit, but if the cable is unable to support current, the consumer i.e starter motor won't work so you need an efficient way to test it. 

Don't spike any wires as this will cause moisture to enter and results in black wire corrosion. Always back probe at a connector plug with the correct size probe so you don't cause any wire or pin damage.

Continuity testing also has its limitations as a 10 strand wire with only one strand still connected (others broken) will show as having continuity making you think the wire is sound, but it won't be able to flow current correctly.

I remember issues with Tiguan and Q3 earth straps causing intermittent non-starts, quick volt drop test identified the problem quickly.

I use a power probe Hook ........... Don't knock it till you've tried it!! It gives at a glance resistance of the circuit, any volt drop in the circuit and has a button you can press to load the circuit to give an instant pass/fail for lives and earths. You do need to know what you are doing with it though, like with any tool VCDS hand tools or the Hook, you can screw the car up IF you don't take your time or don't have an understanding of what you need to test and how to test it. 

Volt Drop Testing...

 

 

Relay and fan testing.....

 

 

 

 

 

Fuel Pump Circuit Testing.....

 

 

 

Sensor ref voltage (5V) short testing ...

 

 

Edited 9 August, 2019 by 3T51704x4

[Laurie61]

On 09/08/2019 at 18:47, 3T51704x4 said:

If what chimaera is OK, look at the Terminal 15 and X contact relays on J519, swap them over as temp check to see if it still does it.

Check volt drop across battery terminal post and the clamp and get someone to crank the engine. this will show up a poor connection between the battery post and the clamp. You can also test the body and engine earth the same way.

One multimeter lead on battery centre post then the other to the engine block or head. If when it is cranked the volt drop is above 0.2V (I've seen an 8V drop on engine earth) you have a bad cable, poor (corroded) connection or broken wire within the PVC. This is a quick test to see if you have a poor connection without wasting time cleaning connections which are sound.

You can do the same to the chassis from the battery negative post. There are two different main earth circuits, body and engine earth. Use these tests for fundamental loss of battery power.

Go from battery positive centre of post to starter main battery terminal (30) to test starter feed (had this been your issue but it is not)

Batt pos to SB fusebox input to check for volt drop.

Batt pos to SC fusebox input from battery.

Batt pos to J519 input etc etc.

Do it in a methodical manor to speed your diagnosis.

As it is intermittent, you need to do these tests at the time you experience the issue which is why these sorts of events are the most challenging to track down.

VCDS scan could also help narrow down your issue like term 15 relay or X relief relay open circuit sporadic etc.

 

Thanks for the input. I am taking the car over to the dealer, Tue 13th, today. I will raise the points mentioned above and see what they come up with. 

 

The car has shown some odd behaviour in the past, such as intermittent heavier steering feel and poor battery charging during a run. I am now thinking all these issues are related.  

[3T51704x4]

If you are having those issues too, forget the relays as on a different circuit. You are looking at loose/broken/corroded main type cable at battery or battery earth, engine earth or on the alternator.

Could even be an intermittent short in the battery itself.

Hairline crack in one of the strip (bolted) fuses in the SB fuse box.

Open the fuse box after running with all loads on for a few mins, use a thermal temperature detector and check the strip fuses for high temp, if you don’t have one, put your finger on the nuts to see if they are hot, the black alternator lead is usually favourite for failing causing a large voltage drop. Can easily be tested if the above info followed.

Edited 13 August, 2019 by 3T51704x4

[justg]

Hi, guys. I am facing exactly the same problem and am not sure what I should do. Does someone know how the problem was solved?