ok, I have bought a 1999 A8. Did a tranny service myself. Which id did not help with the Tranny safe mode situation. Also did not have any PRND23 display on my dashboard.
Thinking this might be an electronic issue, I have tested with a test light all fuses and relays. I also unplugged the TCU without disconnecting the battery to see if there was power going to the pins. Put it back together, I did not turn the keys on (key was left out of the ignition) through out this process.
After putting all back together, I went to start the car and nothing, no crank, no engine light, no start.
Unhooked the battery and hooked back up in 5 minutes. The PRND23 came on the dashboard display. Still no start, no crank or engine check light. I hear the fuel pump, and the starting relays clicking. There is power going to the starter but no signal initiated in the signal wire going to the solenoid. I have even wiggled the shifter thinking of the neutral safety switch. It is like the whole car is in a safe mode. BTW the car was running before I checked all of the fuses and relays....HEEEELLLPPP. Any ideas Please????

 

SO..... you haven't scanned for fault codes, did a trans flush yourself, (knowing most likely nothing about the ZF transmission) and now you can't start your car? LOL

As far as the no start concern its probably not related to anything else wrong with the car. Take apart the ignition column and check the voltage going out of the ignition switch while cranking, its most likely the red wire with the blue stripe...maybe someone with a D2 wiring diagram can chime in and verify.

As for the transmission, if you don't own a vag com you're spinning your wheels. You don't know the process of changing the fluid (yes there is a process) and you don't even know what the cause of the problem was in the first place.

 

Super, thanks for the response. Yeah I know I was asking for trouble doing my own tranny service, unfortunately that did not fix my problem and I have created a new one. I have ordered a vag com to check for codes, but while I wait I was under the impression and correct me if I'm wrong, the ignition switch shouldn't have anything to do with the engine light coming on the dash board while key on.
Like I have mentioned I have absolutely no check engine light, yet I hear the fuel pump, fan running, relays switching.
I will check the red with blue stripe wire like you say this weekend, but appreciate your input on the no engine light...thanks a million

 

The ignition switch to the starter is a simple circuit, it shouldn't trip an engine light, however a problem with the transmission WILL, there everything is monitored.

The ignition circuit really hasn't changed since the invention of the relay.
It goes from a switch, to a relay then directly to the starter solinoid.

 

Ok, I went ahead and pulled the steering column appart. Tested the red/blue thin wire coming out of the ignition switch, it is sending signal, the ignition switch is also getting power. I went ahead and fed power to the signal wire going to the starter solenoid and the car started. I shut it off and would not re-start. Again I by-passed the solenoid and the car started, ran just fine for about 10 minutes and drove, which afterwards decided to shut off like you turn the key off. We tried to restart by bypassing and it only crancked, no fuel pump turning on, ignition switch signal and power still checks out. Is this immobilized? Next I am getting to check the ECU relay, if any other suggestions, please let us know. Also hooking up the OBD II this weekend and ordering the Bentley manual. Please LMK if any one has any suggestions. Thanks you guys, this car is a nightmare.........

 

You have an electrical problem in a car that sets the standard for electrical systems.

You need to either bring it in or change your way of diagnosis.

You do not need to check if the car drives you need the car to send power to that wire when you turn the key.

First scan the ECM for fault codes with a VAG-COM the generic readers can not and will not read all of your codes.
So what's the sense of going at it with half the info?
Do a search some guys have a cheap way of making one work off ebay. I have the Ross-tech.

You checked your fuses, right.
Does your key have fresh batteries???
Is it new??
Do you have a spare you can try?


It Does sound like an immobilizer issue. If it wasn't before it sure will be now.

 

I don't think you have the signal wire, its one of the largest wires coming out of the ignition switch. Try this, look at the signal wire at the starter solinoid, it should be the same color as the one coming out of the ignition switch. You can also check for 12V's on that wire at the starter while someone else tries cranking the engine. If there is no voltage there, it has a break in the circuit from the switch to the starter.

Go back to the ignition switch and re-check the signal coming out of it, if it is indeed sending 12V's out of that wire, then you have to locate the load reduction relay under the dash board and test it. It should be a small 5 or 6 pin relay with that same wire color going into it. Of course once you find it, and you don't know how to test a relay, you can jump it by redirecting power from a different wire bypassing the relay, it should fire the starter. You can also check the wire signal from the ignition switch to that relay with an ohmmeter.
That all checks out, you need a relay.

It wouldn't start if it had immobilizer, you can't bypass the circuit. If it were a immobilizer problem the car would start, then immediately turn off a second later with a yellow light flashing on the dash board that looks like a car.

 

Thanks you guys for all of the input. Last weekend we got some answers and hopefully solutions. According to the Bentley repair manual our Audi 1999 A8 did not come equipped with an immobilizer, that started in 2001.
Also followed some schematics and wiring diagrams which lead us to the following conclusions. Ignition switch checked out constant power wire and the big black and red signal wire had 12.86 volts. Also the wire feeding the starter relay also had good power as did the wire to the load reduction relay.
Next we checked the fuel pump relay, I started out with checking power to the FP fuse. No power, traced the wires to the FP relay. The fuel pump relay had again constant good voltage feed wire, along the small brown with green coming from the Ecm was giving signal to the relay. The relay clicked on and off, which made the fuse power wires blink on off, especially when I lightly tapped on it. So at this point we are ordering a new fuel pump relay.
We had also checked out the Red and black signal wire to the solenoid. No power. Found the starter relay which was getting power and signal from the ignition switch, traced it as far back into the firewall as I could with a good 12 volts. My next step is to trace it from the solenoid to the firewall if the fuel pump switch does not work. Sounds like we have two different issues. We also hooked up a generic OBD II ( I know it's not a Vag, but now we know we have communication with the ECM) we did get misfire codes and one incorrect gear ratio code.
Also will check the ECM J271 relay if we hit a dead end again. Did bypass a wire from the signal wire at the starter relay to the solenoid wire and the damn thing cranked.
Do have question the Bentley is very vague on the relay locations, nothing matches up with the pictures. I have attached our relay tray lay-outs, can anyone tell me where the load reduction relay lies....
Any and ALL suggestions are welcomed.

 

It is vague...calling the panel "central electric", instead of "panel under footwell"...but what seems to be consistent is the Load reduction relay is supposed to be at the opposite end from the Fuel pump relay on the same stretch of 6 relays (or relay outlets)...#1 location Load R and #6 Fuel R. Best I can read on my Bentley(?)

 

You are overthinking the circuit, the fuel pump relay has nothing to do with the ignition switch to starter circuit. It can ONLY come from the ignition switch to the relay, then stright to the starter. Since you jumped power to the solinoid and it cranked that eliminated your problem down to just the signal wire.

Now here is where these stupid cars get tricky, there can be "mulitple" wires the same size and same color under the dash that go to completely different things. I had this problem trying to diagnose the same damn thing on my A4 without the diagram.
You probably haven't found the right relay, from the looks of your provided pics it would be the size of that small grey one on the bottom right.