I'd first check the battery voltage, then, with the negative meter lead on the battery negative terminal, use the positive lead to measure various points that should be at battery voltage, like the supply of the light switch, ignition switch, anything you can access. By doing this, you will be checking out the earth confections, (assuming the battery looks good).
Suggestions on here are practical, but just guesses. We need some real information to point us in the right direction.
Mac.
It’s very well insulated in the boot area surrounded by polystyrene & one or 2 floors.Bare in mind that 3/4 years is quite old for a battery, even a decent one. I know they put the battery in the boot for weighting issues, but it can be cold down there instead of nice and toasty by a hot engine for it's whole life.
Just a though
Interesting cheersIt’s very well insulated in the boot area surrounded by polystyrene & one or 2 floors.
That’s why the original Varta units last so long (17years) in my case.
Hth
Keith
Hi Mac,Insulation only slows the rate at which heat is lost or gained, depending on the relative temperature either side of the insulation materials.
However, if a car is out in the cold overnight, the battery will drop close to the ambient, regardless of the insulation.
The 17 year old battery would have been past it's best well before the icing is dry on the 17th birthday cake. It's a bit late when your out on a cold day or night, and the car won't start, 'cos the battery is dead!
Should be checked as part of the service routine, and changed before it leaves you stranded.
Mac
Still think relay location 9. Removing and refitting it only does not completely prove anything. You need to check it with a meter and if possible open it to see if there are any loose contacts that fit into the relay holder or if any contacts inside the relay are burnt or even welded shut. Dropping in a replacement known good relay may be the easier option.
№ | Designation | A |
---|---|---|
A | Strip fuse for glow plugs (engine) (S39) (applies to engine code ATL) | 40 |
A | Engine control unit fuse (S102) (applies to engine code BAD) | 30 |
A | Strip fuse for glow plugs (engine) (S39) (applies to engine codes AMF, ANY, BHC) | 60 |
B | Engine control unit fuse (S102) (applies to engine code ATL) | 10 |
B | Air mass meter fuse (S74) (applies to engine code BAD) | 5 |
B | Engine control unit fuse (S102) (applies to engine codes AMF, ANY, BHC) | 10 |
C | Fuse -1 - (30) (power steering) (S204) | 80 |
Relays | ||
1 | Terminal 30 voltage supply relay (J317) (applies to engine code ATL) | |
1 | Motronic current supply relay (J271) (applies to engine code BAD) | |
1 | Relay for glow plugs (J52) (applies to engine codes AMF, ANY, BHC) | |
2 | Automatic glow period control unit (J179) (applies to engine code ATL) | |
2 | Terminal 30 voltage supply relay (J317) (applies to engine codes AMF, ANY, BHC) |
Hi terrywindy1,On the older Audi's that I own .
All these problems can be caused by a broken ignition switch, the part that plugs to back of the key barrel. Fairly easy and cheap repair on old Audi's ,never done one on an A2.
Hey, check out MEYLE Ignition- / Starter Switch in the AUTODOC app https://m.autodoc.co.uk/meyle/2117021View attachment 73693
It's unlikely to be the battery if the car starts since the starter motor is by far the largest load and OP says the starter turns strongly. I would rule it out all the same - voltmeter should read a stable 12V+/-0.5V with ignition in pos II (light load) nor should it dip much below 11V with headlights on or during cranking. Saying that, I only just replaced the original 18 year old Varta battery and as it turned out unnecessarily - my problem turned out to be a bad starter motor earth (the one behind n/s headlamp).
The erratic dashboard does suggest a power supply problem, which leaves poor/intermittent connection as one possibility - either on +ve 12V supply side (relay/connector/wiring), or a bad earth (in connector/wire/earthing point). If it were an intermittent short you might expect to see / smell smoke.
As PlasticMac says, check any +ve supply points with respect to body/-ve battery terminal. This may identify a problem on +ve supply side.
To find a weak earth, measure voltage at equipment locations where it is supposed to be battery -ve (earth) , relative to the battery -ve terminal itself. Good earth connections will show 0V (or millivolts of noise). If the connection is bad you will see "ground bounce" - local earth potential going up relative to -ve battery when equipment is switched on and starts to draw current.
The A2 has "decentralised electronics" - e.g. power steering controller and steering angle sensor, door control units, parking sensors, dashboard etc are all networked on a CAN bus. Excessive electrical noise (e.g. ground bounce due to a bad earth) can scramble communications on the CAN bus, with unpredictable results. I had a faulty J387 door control unit once, symptoms started with electric window opening by itself randomly on frosty mornings but within a few weeks everything was going nuts - interior lights would turn on and off randomly, fuel flap would not operate, alarm was randomly going off, dashboard display would not show if doors were open or closed.. Unplugging the connector for the door from the CCU immediately stopped the symptoms in the rest of the car. Suppose it's a possibility also that the ECU or dashboard gateway is faulty.
Good luck,