TDI90 erratic electrics - now Fixed!

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.
 
I did a few more checks this afternoon, removed lower dash to check relays as suggested by @audifan... relay in number 9 was removed and refitted and could have made a difference because then the car did start. It was working briefly but the power steering wasn't working when it was running so something was still not right. Locked the car and went back to it half hour later and still erractic electrics as before. I'll leave everything exposed for now anyway...

When I thought more about it I think I may have had the battery charger connected at that point so maybe this now points back to the Varta battery being the problem even though it is only 3 or 4 years old. I'll do some more checks tomorrow.

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.

Cheers Mac, I've borrowed a meter and I'll try and do some meaningful checks on the car in the coming days, thanks for the advice, appreciate it.

Kennedy
 
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
 
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
It’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
 
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
 
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
Hi Mac,
My point was that the varta original batteries in our cars last an incredible amount of time in their location if you
compare them to general vehicles, not withstanding general maintenance checks etc.
If problems are encountered then replacement as required .
Hth
Keith
 
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.
 
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.

Good shout... we’ve got a TDI75 parked out front so am I right in thinking I’ll find the same relay in that car, 370 in spot 9?...

I will indeed get the meter on my connections as well even though I don’t really know what I’m doing ?... but I will have a poke around anyway.

Nicking a relay off the wife’s A2 is obviously an easy thing to try, I can do that tomorrow or Weds.

Kennedy.
 
Cheers for comments on batteries as well.

I know batteries can fail after a few years but I think the Varta F19 should be a decent choice for a battery that will last. My wife’s TDI had the same battery fitted a few years before mine and that ones okay. Like a lot of owners on here, pretty sure it was the original Varta battery I replaced so there must have been at least 10 years on that one...

So yeah hoping not to have to buy another one!

Kennedy.
 
Even battery as good as the Varta can loose capacity and charge if it's not regularly charged, or there is a constant, low level current drain somewhere.
Low volts due to poor charge or high resistance is still my bet.
Mac.
 
The other important relay is relay 1 in the 3 relay holder

Relay carrier (3-point)


Relay carrier (3-point): Audi A2 (8Z; 1999, 2000, 2001, 2002, 2003, 2004, 2005)


Relay carrier (3-point)
DesignationA
AStrip fuse for glow plugs (engine) (S39) (applies to engine code ATL)40
AEngine control unit fuse (S102) (applies to engine code BAD)30
AStrip fuse for glow plugs (engine) (S39) (applies to engine codes AMF, ANY, BHC)60
BEngine control unit fuse (S102) (applies to engine code ATL)10
BAir mass meter fuse (S74) (applies to engine code BAD)5
BEngine control unit fuse (S102) (applies to engine codes AMF, ANY, BHC)10
CFuse -1 - (30) (power steering) (S204)80
Relays
1Terminal 30 voltage supply relay (J317) (applies to engine code ATL)
1Motronic current supply relay (J271) (applies to engine code BAD)
1Relay for glow plugs (J52) (applies to engine codes AMF, ANY, BHC)
2Automatic glow period control unit (J179) (applies to engine code ATL)
2Terminal 30 voltage supply relay (J317) (applies to engine codes AMF, ANY, BHC)
 
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,
 
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/2117021
Screenshot_20201201-030221_Chrome.jpg
 
Last edited:
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
Hi terrywindy1,
Had this on our A class as well normally caused by big / heavy key ring!
Hth
Keith
 
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,

Very informative post, we’re learning today!... gives me another bunch of things to try this week for sure.

If I still can’t make some progress on things I’ll either need to get lucky on starting it and taking it to a garage or see if there are any A2 experts in the Coventry area willing to stop by my house to lend a socially distanced hand on it... but not giving up just yet.

Thanks again chaps

Kennedy.
 
If you are prepared to travel around 60 miles you could give WOM a call and explain to them the problem. They are based near Stoke. They come highly recommended on here.
 
I've read your original post again, and I'm thinking dashpod. I know, as a Mk1 TT minder, dash pods can be a pain. Just wondering if you have a dash pod repair co not too far away, that could check it out for you? If not post it to Patryk at Totaltronics, or, better still, give him a ring, and ask his opinion.

Mac.
 
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