TDI90 erratic electrics - now Fixed!

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.
Ha ha - I read that as dash-pot. I was thinking, WHAT! the Audi TT's have a carb with a dash-pot!!

er, no
 
Little update on this one as I braved the cold this morning for a few more tests.

The relay that we have been discussing in holder 9 (printed 370) appears to function, I haven't had chance to swap this with one in our other TDI but it feels like contacts are operational inside (on the key turn) when touching it. A test with the meter shows power to the relay's in that block is matching battery voltage in all cases. Nothing appears damaged or melted there.

Battery I still feel is probably okay, I put the charger on it anyway and in less than 30 minutes on slow charge the charger displayed 'full'. Voltage battery voltage is 12.5v, minor drop of voltage with lights on etc but never below 12.3v ish and starter motor is still turning easily.

Removed, cleaned up and refitted starter motor earth (to earth point behind N/S head lamp), only because I thought it looked a bit crusty the other day so wanted to make sure that was okay. Didn't get time to do further checks with meter on Starter Motor itself, reverse light switch etc... will have a look tomorrow.

Kennedy.
 
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)

Thanks for highlighting this, where will I find this bank of relays?? Are they in passenger footwell with ECU, comfort unit etc?
 
I still think that battery is too low - they should be around 14 volts when engine is running

That’s just the standing charge on it, I can’t get the car running currently to see the voltage... last time I got it to start was a week ago.

I might borrow the battery off the wife’s A2 in the morning even though it’s about 4 years older than mine... but there’s been no signs at all of a sluggish battery on that car so feel it’s a worthwhile swap just to see. You never know.
 
Just because you can hear a relay clicking does not mean the internal contacts are in a good condition as they could be corroded or burnt.
 
Just because you can hear a relay clicking does not mean the internal contacts are in a good condition as they could be corroded or burnt.

Yeah makes sense. I’ll swap that relay tomorrow along with the battery both from my wife’s TDI just to rule these things out and then I’ll move onto the other relays as discussed and start checking other switches and connections I can access.
 
A good battery should be around 13. 8 volts, no load, and shouldn't drop below 12 volts under load.
The fact that the starter turns over well, may be miss leading, as it has dedicated supply, (to handle the high current), and may not reflect the connections (pos & neg) to the rest of the car.
Mac.
 
I’ve swapped battery and relay with my wife’s TDI this morning and all is the same. There’s never been a problem with the Varta F19 on my wife’s car and if anything the standing voltage is slightly lower than my battery. Obviously I can’t do a proper load/drop test currently but with the starter motor still turning strong I’m inclined to say battery is probably okay.

I’ve found that the power to headlight switch is reading 12v (car not running) with multimeter but on stage one of the ignition key turn the power drops to zero, then with the lights switched on it’s a negative reading. Is this suggesting a bad Earth relating to that circuit?

K.
 
A good battery should be around 13. 8 volts, no load, and shouldn't drop below 12 volts under load.
The fact that the starter turns over well, may be miss leading, as it has dedicated supply, (to handle the high current), and may not reflect the connections (pos & neg) to the rest of the car.
Mac.

Good afternoon Mac, I posted above before seeing your comments if you were wondering... so I’ll take your point about the starter motor on board.

What are your thought regarding the drop of power at the headlight switch?
 
Good afternoon Mac, I posted above before seeing your comments if you were wondering... so I’ll take your point about the starter motor on board.

What are your thought regarding the drop of power at the headlight switch?
I agree that the battery is (probably) not the problem.
Can you expand on the light switch measurements a bit? Where are the meter leads, especially the neg (earth) being held?
Mac.
 
I agree that the battery is (probably) not the problem.
Can you expand on the light switch measurements a bit? Where are the meter leads, especially the neg (earth) being held?
Mac.

Hi Mac, yeah I was probably testing it wrong, but I basically just used the positive and negative terminals in the back of the connector block to test for voltage... now I think the idea is that the negative multimeter probe should be on a reliable battery negative or the actual battery negative itself... ??‍♂️

Latest detail on the car is...

After a check of the under floor relays, namely relay 1 or position ‘A’ as I think it’s marked I thought I’d give the key a turn and really everything behaved exactly the same apart from...

the starter motor continued to turn over and over continuously WITHOUT key in ignition and the ignition off!! - Couldn’t do much at that point, smelt some electrical burning in the car but couldn’t see signs of shorting etc on anything exposed or any smoke - but the battery soon slowed and then there wasn’t enough power to turn starter any more.

Small amount of smoke visible from starter motor area, again, can smell the electrical smoke round the front.

I have had issue with the reverse lights cutting out the car and reverse gear selection also disabling all power at start up. I notice the cabling for starter and reverse lights are routed together, seems like another possible cause.

K
 
the starter motor continued to turn over and over continuously WITHOUT key in ignition and the ignition off!!
There's a live feed from the battery to the starter - it's live all the time! So you must have a short between the live terminal on the starter (which should be insulated) and the solenoid.

RAB
 
There's a live feed from the battery to the starter - it's live all the time! So you must have a short between the live terminal on the starter (which should be insulated) and the solenoid.

RAB

Hello Rab, cheers for input. What you said does correlate with where I think the smoke was originating, not lots but a little bit of lingering smoke was visible and it smelt like electrical shorting.

Would it be likely that a faulty ignition switch could be providing unwanted power to the relays/solenoid??

I’m still looking at that but realised the steering wheel might have to come off before removing the lower steering column cowling in order to remove the ignition barrel/switch - can anyone confirm if this is the case?

Thanks
Kennedy.
 
First thing to do is to check whether you are getting 12v to the solenoid when you try to start. If not check everything between the solenoid and the ignition switch - you will need a circuit diagram. You'll need to remove the steering wheel to change the switch. Disconnect the battery before removing the airbag.

RAB
 
Does sound like a serious short circuit between the starter and reversing lights harnesses. I would start there, make sure the looms are separated then check damaged insulating and burnt wires, carrying out any repairs as necessary. Once that has been done then you can continue with any other issues remaining. As the starter is permanently live I would disconnect the battery to prevent a short going un noticed and possible causing a fire.
 
The relay chatter and the dash board disco lights suggests one of two things:

- faulty electronics that controls the relay (ECU/CCU). It is possible to start and drive the car with the CCU completely disconnected, I did that once before I realised it was unnecessary in my case. It would rule out CCU as primary/secondary* cause. I do not know if it is possible to swap ECUs, someone else here may know.

- (locally) weak power supply to the electronics, dropping below minimum as soon as the relay is energised thus causing the electronics to reset and a new cycle to begin. This could be a short somewhere in the wiring, not sure how likely that is, but also may be a weak earth or a weak +ve supply connection. This can really be a number fo things - broken wire, oxidised contacts in connectors, dry joint on a PCB, corroded earth point.

We know that the starter motor supply is good, that needs very high current to operate so the connections are all good there. The suspected supply problem would be closer to the electronics clusters ie. ECU, CCU, dash board cluster (because the CAN bus hub is apparently located there). Unfortunately if the problem is dry joint or connector related then you will not be able to see that by measuring supply voltage on the outside of the circuit, you would have to know where to look on the PCBs inside.

The electrical wiring diagram for the TDI should be of help in locating potential earth and supply weak points that are relevant to the ECU/CCU/dash board cluster.

* by secondary cause I mean something can appear to be the cause because when it is disconnected the problem goes away, but it may be that it is the additional load on the power supply that makes the difference thus making the power supply weakness the primary cause. So for example the reverse lights may be such a secondary cause.
 
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