Changed Battery - Now EPC/EML won't go out (1.4 Petrol)

mjsbrabus

A2OC Donor
I think I had this before after a flat battery but can't recall how it was rectified.

I know that flat batteries cause all kinds of gremlins. My recollection is that the lights just decided to go off themselves after a while last time?!

The fault code that has appeared after battery change is the 17556 - G71 sensor implausible signal which I think I have had before from time to time but not for a few months. Tried to clear with code reader but seems to come back.

Car driving fine but idle is not steady on start up. No issues before battery change. Any ideas on how to get these lights off?
 
Update - no response needed. Just been to put the car in the garage and both lights extinguished.

So I guess the car and the battery have now decided they like each other and are talking.

You have got to love A2 electrics!!!!!
 
Low voltage or amperage can cause various problems with the A2. Its early computer system and fairly basic ( by todays standards ) way of alerting the driver to problems can be a problem. Quite often when the computer detects low power it either shuts down that part or puts it into a fail safe mode. When power is restored e.g. by charging the battery, the car still thinks the fault is there. When you use the system by driving the car the sensors often recalibrate themselves and if reading now are within expected limit the warning disappear as the computer resets itself.
 
My auto electrician loaned me a battery jump lead which fits into the diagnostic port and the other end into the socket on a jump start unit.
Brilliant and only £7 on Amazon.
Such a simple solution to a potential problem on any car and once fitted you can take as long as you like swapping batteries.
 
I'd use the cigar lighter socket in preference to the OBD socket. I'd not be happy putting any voltage on an OBD socket, ever. It's a low level output, direct to the controller, whereas the cigar socket is direct to the battery via a hefty fuse and big wires!
Mac.
 
Sorry to jump in on your thread but, I have 4 A2s and each have old and well used batteries, not one of them is fully charged at any one time unlike a new battery would be but only one A2 shows any signs of complaining, the other three just get on with it.
Even swapping the batteries around makes no difference.
 
Thanks for your comments Mac. But perhaps my auto electrician prefers powering through the diagnostics port because on some cars the cigarette lighter socket is not permanently fed and switched via the ignition. Think all VAG are though ?
 
I'd use the cigar lighter socket in preference to the OBD socket. I'd not be happy putting any voltage on an OBD socket, ever. It's a low level output, direct to the controller, whereas the cigar socket is direct to the battery via a hefty fuse and big wires!

Not true. The diagnostics have a 10A fuse and the lighter socket only 15A. If you have a modern VW, you have to use the OBD socket as the lighter socket is dead when the ignition is off.

RAB
 
I was referring, specifically to the A2, and owners who would do their own battery swap. A mechanic, who works on many brands would use a general purpose tool, and maybe, the OBD port. I would not connect a high current source, such as a jump start unit, to anything other than a battery via jump leads. An ECU would be destroyed before any fuse blew. The fuse that protects the ECU/OBD circuits is in the supply to those circuits, it provides no protection to the low current 12 volt output from the OBD socket, which is only intended to power the OBD lead.
The lighter socket is the safe way to charge the battery, and back up the electronics.
Just my opinion, obviously!
Mac.
 
Perhaps I didn’t explain properly.
The device off Amazon fits into the diagnostics port and the other end of the lead fits in the cigarette socket of the jump start unit!
Does this make sense ?

Cheers

Steve B
 
You are still powering the car back through the OBDII port. I really do not think Audi designed the A2 to be reverse powered that way, the CAR 12v socket is a much safer option. Another point on later Audis that have an ignition switched 12v socket is they all have remote jump start points under the bonnet whether the battery is in the engine bay or in the boot.
 
I was referring, specifically to the A2, and owners who would do their own battery swap. A mechanic, who works on many brands would use a general purpose tool, and maybe, the OBD port. I would not connect a high current source, such as a jump start unit, to anything other than a battery via jump leads. An ECU would be destroyed before any fuse blew. The fuse that protects the ECU/OBD circuits is in the supply to those circuits, it provides no protection to the low current 12 volt output from the OBD socket, which is only intended to power the OBD lead.
The lighter socket is the safe way to charge the battery, and back up the electronics.

Of course you wouldn't put a high amperage through the socket, just as you wouldn't through the lighter socket. That wasn't the original question. The live and neutral connections on the OBD socket are direct connections to the battery, via fuses; they are not connected to anything else. So they are perfectly safe to use with a 5A charger.

RAB
 
Of course you wouldn't put a high amperage through the socket, just as you wouldn't through the lighter socket. That wasn't the original question. The live and neutral connections on the OBD socket are direct connections to the battery, via fuses; they are not connected to anything else. So they are perfectly safe to use with a 5A charger.

RAB

I was commenting on this:
"... auto electrician loaned me a battery jump lead which fits into the diagnostic port and the other end into the socket on a jump start unit"
Mac.
 
Think there are some crossed wires here.
I read it as the jump start unit was just a convenient power source to prevent any 'memory settings' being lost while the battery was disconnected, and not to literally 'jump start' the engine

Cheers Spike
 
Think there are some crossed wires here.
I read it as the jump start unit was just a convenient power source to prevent any 'memory settings' being lost while the battery was disconnected, and not to literally 'jump start' the engine

Cheers Spike
Hi Spike,
That's how I read it too. However that jump start unit will have the capacity to supply in excess of 100 amps, no current limit.
Crossed wires? Doesn't bear thinking about..
I'll stick with an old PP9 I think.
Mac.
 
Hi Mac
It's always good to do what you think is safe so stick with your 9v supply.
In reality the current draw is limited to the demand of any particular module regardless of how big a power supply it's connected to. That's just how the car's battery works. It has around 800 amps (the CCA rating) available but when you switch on the interior lights for example it only draws the odd amp or two needed for the bulbs.
RAB pointed out the L and N pins within the OBD socket are fused and only connect to the main battery circuit so any module with memory settings is fed in the normal way via the cars individual fused circuits.
It would be interesting to know if the OBD connector used is fully pinned or only has the L and N pins installed

For newer cars with battery management systems I suspect a 9v back-up supply would not be sufficient for many memory setting circuits. The system progressively shuts down modules to save the diminishing battery power for the high priority circuits, which I think have a higher much voltage threshold.

Cheers Spike
 
I understand your points. Just seems high risk to me, given there is an easy, and safer alternative in the cigar socket. I see the OBD socket as a very low current output. The cigar socket is big wires, high current, and a big fuse, nothing else.
In a previous life, a colleague hooked up 10 bits of avionics wizardry (this was 1970 ish), to a big PSU (rack mount big dials, lots of amps etc) for testing. Switched on, nothing. Wound up the current trip, still nothing. Asked for advice, long story short, he'd got his Pos and Neg crossed! Followed very long night, lots of soldering, climbing over roof to raid the stores for bits, and convoluted explanations next day. It's stayed with me ever since! Perhaps that colours my view on this!
Mac.
 
I was commenting on this:
"... auto electrician loaned me a battery jump lead which fits into the diagnostic port and the other end into the socket on a jump start unit"
Mac.
I believe that you have misinterpreted the above. Jump start units usually have 12v outputs but not for jump-starting! So in other words, you can charge the battery from a jump start unit, if desired.

If you look at the wiring diagrams for an A2, you will realise that using L&N on the OBD socket is no different to using the lighter socket. The other pin connections are unused by the plug and therefore there is no connection whatsoever to the ECU/OBD. The lighter socket fuse is 15A, so is definitely not big amps. The OBD is 10A so is not a very low current output/input.

RAB
 
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