Red lights come on and stay on.
 

Car is a 2000 model FL S8. 148,000 miles and driven gently by me for the last 10 years.

Today, which was hot c.37c, just as we moved off, the car made a thump and all the 'PRNDL432' lights went red.

Car drives and reverses but no kiickdown and the autobox isn't changing as it used to. It wont kick down or even change down, I think and 'Sport mode' isn't working.

If I switch off, it starts normally and moves off ok (in first I expect) but the change up to second is accompanied by a thump and then the red lights come on and stay on.

Once the lights are on, selecting a "D" or "R" while stationary is accompanied by the same thump.

Is my car a gonner?

edit. Reading through other threads, reverse seems to precede this sort of thing. In my case. all was normal as I reverse parked. The problem first occurred 10 mins later when I drove out of the parking spot.

Interesting symptoms. Its going in to limp mode which is why it won't change or kick down, but doing it at the change to 2nd gear is unusual.

The first thing to do is scan it for codes. Second thing to do is make sure the TCU isn't wet.

How does it behave in tiptronic? Put it straight in to tip from startup and without moving, then pull away and see what it does and whether it will change gears manually.

Its not the F125, and doesn't sound like a clutch drum as that usually manifests in 1st. I'm wondering whether its a solenoid fault, and that is very often caused by a wet TCU.

After reading a bit on here, Tried the car again. No change.

Shut it down, restarted and tried it in Sport mode only. So selected 1 and moved off. box changed up through the gears as requested properly, and changed down properly too. I then reversed to turn. All ok.

Put the thing in "D" and drove home with the autobox working normally and no red lights.

So must be an intermittant F125 fault maybe?

Hopefully not a gonner yet!

Edit to add MikkiJayne, I missed your reply, but interested to see what you think now.
I can't easily scan it for codes as don't have the kit here. Don't think the TCU is wet as its hot here and hasnt rained for weeks. We are in Bulgaria now.

In "D" (when the fault was happening) it started in first, then changed to limp mode gear when it should have been changing to second- but now the thing is back to normal. So whatever caused the problem has gone away!

That does sound like an intermittent f125 fault: I had similar with my S8 a few months back after a period of gentle, and infrequent, use.

The problem went away after some more "spirited" driving, including the use of sport mode, and some "manual" shifting of the tiptronic, so hopefully your issue will disappear in the same way.

PS: I also had the f125 contacts cleaned by my local garage, and haven't had an issue since.

Thanks Tin Tin.
Now that I've realised I can 'cure it' by using tiptronic I feel a bit better.

I just paid 1200 quid to have the thing shipped to Bulgaria, so it'd be a right PITA if it croaked on me!

F125 problems happen when you move the shifter, not once its already in gear and moving.

I still have a beer voucher on a valve block solenoid intermittent code due to water ingress. This is a D2 remember. If Elon wants to find liquid water on Mars he should send a D2 with the scouting party :ROFL: The electronics box is probably full of condensation.

Thanks MikkiJayne. I'd best have a look for water ingress then. But where is this electronics box?

I can confirm that the fault does not come when you move the lever. Only about 100 yards after you move off.
The car has been here in warm, dry Bulgaria for a few months, but before that it stood outside in Scotland unused, for 18 months. There was some water ingress to the boot, caused by a perished bung, in the boot gutter side. Is there anything in the boot that could cause this?

dingdingding!

The electronics box is the black plastic lump at the base of the screen on the left. There are a bunch of philips screws holding the lid on which are almost certainly seized in place if it's sat for that long, but worth a try. The TCU sits at the top and is not water-tight, unlike the ECU, so has a tendency to be the first in line for condensation damage. Its a bit of a pain to get to, but if you can remove the connector its worth looking for corrosion there first and giving it a spray of WD40. Sometimes that will help it, but sometimes there is internal corrosion too. Have a look for my General Vod workshop thread - I show the process in there. That one got scrapped for a blown gearbox whereas in fact it was just water-borne deposits on the TCU pcb. I cleaned it with isopropyl alcohol and a toothbrush and let it try overnight and it worked perfectly +++

Btw, I sell replacement boot grommets here: https://www.ebay.co.uk/itm/153918842338

https://i.ebayimg.com/images/g/xekAA...bT/s-l1600.jpg

Hi Mikki.
Ok, I'll have a look in that box for water etc.
I need a couple of those grommets, so will buy as soon as I have a UK shipping address. We are in Bulgaria and shipping anything here from outside the EU is a pain.
Sorry for late response, last night we had a major storm here and lightning must have struck the mast-thus no internet.
I'm just relieved that its not 'curtains' mechanically for the box....yet. I really like this car.

Ok. got the lid off and it's clear there has been moisture in there. very light rusting of steel parts, and typical alumium corrosion, but not much.

I take it the engine ECU is nearest the wing and gearbox item nearest the middle of the car?

It is. Getrieb = transmission!

Oh dear.

Scooshed some WD-40 in there, and refixed the cover- seeing as the fault had gone away.

Took it out on the road and not only is the fault back, but it also does it in tiptronic now too!

I guess next step is remove the TCU and clean its insides?

How the heck do u remove the TCU wiring connector???

Just picked up on this thread - 37 degrees in Langbank - really?

We moved!
In Bulgaria these days after the job in Kazakhstan ended. My S8 is here now, Tiger will be here (hopefully) in a week.
Actually, I think the heat might be a factor here. Certtainly the ESP/ ABS goes on the blink when it's too hot, but behaves in cooler weather.

Unscrew the TCU bracket (two screws at the front) so that it can be lifted towards the front of the car, then unbolt the TCU from its bracket (4x M6 nuts). You may need to lift the ECU out to get the TCU wiring free.

Thanks Mikki.
I shall report back.

Well, I re-racked the TCU. no difference.

Now took the top off it, looks great inside...

tried the toothbrush and rubbing alcohol on the side you can see, and tipped some down the inside too...

Next, I'll drink the rubbing alcohol if it doesn't work...

hmmm. Board looks Ok at a glance, but looking through a triplex loupe, there's clearly corrosion and deposits all over the place.

I'll let it dry and then put it together, but I think it's likely 'Donald Duck'd' A8 parts don't have a replacement.

Part number is 4D0 927 156 BN

OK put it back in, no joy. Now what do I do!?

Update.
Cleaned the TCU more and more. Went at it with isopropyl alcohol, toothbrush, cotton buds and scraped between tracks where it looked like it might be corroded.
Fitted it two or three times- each time 100% faulty in tip and auto.

Got bored and decided to fix the two damaged brass ferrules on the box that contains the TCU/ ECU and ABS, so at least once repaired, new TCU might stay dry. I cut a slot to screw them in and bedded them with Superglue.
Decided to build it back up properly and just use it in limp mode while trying to find a new TCU. Flooded the TCU with WD-40 and dusted the terminals with a diamond file.
Built it back up.

Decided to enlist some proper help and said a prayer to God that somehow it would work!

Tried it in tiptronic- still knackered.
Restarted and set off in 4th. Went OK! Drove it in tip and in Auto.
All OK! :-)

Don't know if it'll stay fixed, but all OK for now.
Maybe it just wanted attention??

Gave thanks to God! ('Cos I don't think it was me....).

Well, it didn't stay fixed......;-(

Seems it's some sort of 'startup' fault.

The red lights/ limp mode thing either happens at the first gear change as you move off after starting the engine.

Or else the trip is completely normal.

If the fault is absent, you can drive for hours normally, but the next startup might bring the lights on, with a thump followed by limp mode.

If you start and leave it in tip- first gear- it never comes.
Also, I can start and reverse for as long as I like.

Baffled.

The fault is clearly associated with that first change up- but not all the time.

I had my gearbox rebuilt in 2014.

Some time later it started lighting everything on the dash and went into limp-home mode. Called the gearbox specialist and they said it was definitely an electronics issue. Waited a few months and obtained the replacement TCU (thanks Prestige) and it fixed my problem instantly. My original TCU was immaculate; the replacement was not quite as clean and tidy but it certainly did the job. Still working fine 6 years later.

John G

I checked my car using my OBD Eleven device on the OBD-II interface and it came up with a transmission control unit/module ROM checksum error at the time - hence my actions in getting the unit replaced despite it looking visually perfect.

John G

Thanks John
I guess my TCU has had it too.

MikkiJayne. Reading through the threads on here in search of wisdom, I noted somewhere that you have a box of them
Would you consider flogging me one, please?

Mine is 4D0 927 156 BN

Ta.

Got the codes read and up came "P0758 Shifter Solenoid B: Electrical".

What can cause this?

Is there a cable that could be damaged or nibbled by animals? (a known problem here)- or could it be low ATF level?

Highly unlikely that low ATF would cause an electrical problem with one of the solenoids. Your suggestion of animals is probably more realistic, as I've read previously about how much damage is caused by them. A thorough inspection of the appropriate loom should confirm your suspicion, as well as checking the physical connection to the transmission to ensure it's clean and secure.

Thanks Steamship.
Luckily I have a pit here, so will have a look tomoz.

The Pine Marten is a known nibbler, and if he has been at my car, I shall give him lead poisoning.

This turned out to be a faulty TCU.
A secondhand one has fixed the problem completely.

For info, my car was stored for about 18 months outside in Scotland, but it ran fine for 6 months this year after coming out of storage and shipping to Bulgaria..

The fault appeared out of the blue and became harder as time went by, putting the box into limp mode nearly every journey, but not 100% of the time.

In the end about one start in forty didn't result in limp mode, but the rest did.

I guess it was condensation inside the TCU while it was stored that was at the root of the problem.