intermittent lose of almost everything

06 jetta 1.9 tdi driving along and the inst cluster all goes to zero engine quits push clutch in coast to stop. none of the lights work cept the hazards, the windows work and the courtesy lights work but nuthin else seems to. let it sit few mins turn key n cluster comes back on starts back up and runs for an undermined amount of time before it does it again. until last night... whatever it is finally said fu.

immobilizer - how does this system work on this car?

ignition switch?

ecu? - which puter powers up cluster?

i wanna rip the ign sw out n put a toggle n a push button ha but dont know how those imo things work. does the tumbler get 12v+ or how does the antenna talk to the ecu when the key is near?

i dont have a obd reader or any other reader yes the car had idiot lights on for a while now bulb and airbag maybe even the steering wheel one sometimes iirc

any help greatly appreciated don

Is your location Huntington New York, where it snows and road salt is used and automotive electrical items all take a terrific beating and ground wire connections routinely get corroded? If you do not have an appropriate VCDS and know how to use it, search for a local TDI guru and pay to have someone figure your car's problems out, as other than agreeing that it appears to be a serious electrical problem, the information you observed and reported lacks sufficient detail to draw any further conclusions.

Sounds like a dead battery to me, caused by an alternator that gave up the ghost a day or two ago.

It is very likely you have a loose ground. A common problem on the A5's as they get older. Does not sound like an immobilizer issue. The Immobilizer would still allow your car to start but would shut the engine down in about 3 seconds or so.

There is a major chassis ground located underneath the airbox that can loosen over time and cause the problems you describe. You will have to remove the airbox to get to it. That ground has loosened twice on my car. The second time I replaced the factory acorn nut with a new steel locknut.

All VCDS will tell you is that you have a crap ton of Fault Codes. Kind of a waste of time doing a scan until you make sure all of your grounds are clean and tight.

That car does not have an "ignition switch" in the traditional sense. It is more like a "key position sensor" which sends a signal to the steering column ECU, then to the Central Electronics, which in turn sends the necessary signal to all the other various modules across the CAN bus.

It is quite possible the load reduction relay is bad, in the relay box in the car, which is a little tricky to get to as the lower dash trim needs to come loose for access.

However, as stated above, start with the obvious, and at the source: the battery. Check for voltage at both the underhood fuse link box AND check the grounds. The A5's only ground point from the battery is easy to get at, fortunately, as it sits right up top. But there are also lots of ground points in other places. A manual will show all of them, but the ones you'd be most concerned with are the ones on the steering column/dash brace above the pedals and the ones on the lower A-pillar area behind the hood release. The ones under the air box area, down low behind the headlight, would also be good ones to check, as those get exposed to the elements.

But after checking to make sure the battery voltage is at least 12.5 static AND it is still that much measuring from the body and fuse link box, I would then switch to a scan tool to see if you can find out if the CE actually "sees" the key switched on when it should.

thanks guys

huntington beach so cal - no rock salt here. i dont live on the water but living near it and the car not being kept in a garage corrosion could be an issue

do dead batteries or bad alt cause these cars to act demon possessed? thought once batt voltage was too low a car wouldnt start? (or if it went low while running it would start misfiring?) wouldnt a charge or battery light have come on if the alt died?

when i get the car back here i'll check the voltage and the grounds and report here

thank you all for your thoughts and your time - very nice

Do check the ground under the airbox. Even without corrosion it could still be loose. And the OH's advice is definitely top notch. As he posted, the load reduction relay could defiantly be an issue a well as various grounds........

If you drive a lot of short trips, the battery may not get fully charged and over time battery voltage can get lower causing poor charging. Try putting the car on a battery charger overnight and then revisit the issues.

Your symptoms could be the result of a bad battery or one that needs a charge. If you suspect you have an alternator that is charging low, charge the battery and recheck the charging voltage. Charging voltage should be about 14 1/2 Volts.

If you put a battery on a charger overnight and the charger needle does not go down to 1 to 1 1/2 Amps, (stays at about 4 Amps or so) the battery needs replaced.

oilhammer said:

That car does not have an "ignition switch" in the traditional sense. It is more like a "key position sensor" which sends a signal to the steering column ECU, then to the Central Electronics, which in turn sends the necessary signal to all the other various modules across the CAN bus.

Click to expand...

That's about right, isn't it? When you turn on an electrical device you don't actually turn it on. What you are doing is sending a request or command to a controller (the ECU is a controller) to turn the device on. I think most people don't really understand how vastly different digitally controlled systems are compared to the old analog systems on older cars.

We should have a section dedicated to digitally controlled systems on cars. Some CanBus links for those that want a better understanding of this stuff.
https://www.csselectronics.com/screen/page/simple-intro-to-can-bus/language/en
https://en.wikipedia.org/wiki/CAN_bus
https://news.voyage.auto/an-introdu...o-programmatically-control-a-car-f1b18be4f377

LinBus. A simpler and cheaper communication protocal used in conjunction with CanBus.
https://en.wikipedia.org/wiki/Local_Interconnect_Network

I put a little presentation on at a TDIfest one year, CAN systems, and talked a little bit about that. But yes, the low voltage signal request carried to a controller that actually does the load switching is pretty commonplace for a lot of things nowadays. Good news is, that sublet control also means input/output can be tracked via OBD and bidirectional controls and such. Which is why I get so flustered when I see people here (and elsewhere) waste so much time tearing things apart looking for some issue when 30 seconds with a scan tool will do the same thing.

Certainly some amazing technology. I agree. To diagnose a digital car with any degree of success, you need to be able to access the cars network.

A lot of folks don't understand a scan tools purpose in diagnosis. Even dealer techs are guilty of this. What they will do is retrieve the DTC's and just start replacing components named in the text of the DTC instead of actually diagnosing the problem. Helps them take shotgunning parts to a whole new level.

What I would like to see is a scanner function built into the infotainment/NAVI system. Being that the radio is already CanBus networked, all it would take is for some new firmware written for the radio. It would be awesome. You do the secret squirrel handshake with the system and BAM!!! You're in maintenance mode.

But no, all the car manufacturer gives you on the car is a single spend money light (CEL) and only for emissions related DTC's.

Hmm.. It seems like either the battery is dead, or there is a problem with ignition. Or even both at the same time... Getting information about CAN Bus isn't difficult, but finding the right one can be.

I personally read an article from autopi on CAN Bus twice and it gave me a very useful base of knowledge, exactly what I needed at the beginning. See the article below.