Hi all,

Sorry for the long post but I really hope somebody can point me in the right direction please. My car is a 3.6 TDV8 by the way. Not had a single issue with it in 2+ years of use. Last week I noticed the airbag light came on while driving. When I got home I turned the engine off and back on and it went away. The next journey the light came back on as soon as I started up, and I also had a 'park brake fail' warning for a few seconds. I replaced the battery (new 019, 95Ah, 850CCA), but this didn't seem to do anything.

Next journey I had another new warning 'Transmission fault, only certain gears available' or something, but the car seemed fine. I booked it in with the garage for a diagnostic (that should be this afternoon).

I had to use the car yesterday, same warnings on startup, drove for about 5 miles, noticed the revs were slightly high, weather was bad and traffic was slow but it wouldn't go above 3rd gear (tried manually putting it into 4th). I decided to turn around and head home at the next junction, as I turned around I got 'Unable to use low range transmission' (or similar) followed by 'HDC not available'. The dashboard then went dark, all gauges dropped to the bottom. No other warning lights or anything. As I was pulling into the side of the road the engine turned off. I tried to restart, but every time I put the key in the ignition all I get is a red flashing Park light. If I apply the handbrake it stops flashing and stays on as it should.

When I put the key in it makes the motorised noise as usual, turning to position 1 brings the radio console on, position 2 brings the green displays on but doesn't say anything and there are no lights on the dash other than the flashing park light. Starter position on the key doesn't do anything most of the time, sometimes if you move it through the gears it will allow the starter motor to turn, but runs continually without trying to fire.

I have disconnected the battery, hard reset (terminals together for 10 seconds) left it for 10 mins and reconnected but it is exactly the same. I am hoping to get a tow up to the garage later but not sure if the diagnostics will pick anything up as the ignition appears to be kind of off?

Any ideas as I am totally stumped? I have read lots of vaguely similar posts but nothing quite like this.

I'm a non tech, so don't take me serious, but it sounds to me as an electrical faillure, alternator not loading the battery, voltage to low. This is one of the reasons just to buy the gap diagnostic tool. Helped me out more than a few times. Hope you solve it soon

Sounds to me like a pretty usual alternator failure sir... Charge your old battery up and refit it, this should allow the car to start and to check the charge rate when she's running...

Diagnostic showed multiple modules not able to communicate, these included dashboard, immobiliser, transmission, amplifier (although the stereo seems to be about the only thing working on the car!) And at least 2 others whose names escape me.
I have charged and refitted the (brand new) battery. Battery diagnostic is reporting it to be fine and the car is still doing exactly the same.
Question is what connects all these modules? I am going to assume (by that, read hope) it may be a fuse / relay / connection. I will check all these to start with. Does anybody know where these modules are located? I would like to check them for water ingress etc.

What voltage is the battery showing currently? A failed alternator can take a battery with it and have lots of weird side effects though I'd have expected the garage to check it.

You really need to get a suitable diagnostic tool if you want to work on it yourself. If the voltage is okay I would reset all the faults and see which come back.

Gap IID BT is the preferred option. icarsoft is the more wallet-friendly one. 2016 Skoda Octavia VRS Estate
<gone>2009 FF Vogue TDV8 Buckingham Blue</gone>
<gone>2015 BMW 520D SE (not my favourite car)</gone>
<gone>2009 D3 HSE Galway Green</gone>

I think I may have to invest in a diagnostic tool.

The mechanic did check the battery, it was 12.2v after recovering the car (so low). I have swapped it for a fully charged battery (12.6v) and am charging the one which was on it. My battery tester shows it to be fine. Car is still exactly the same.

On the assumption that it is 1 thing affecting multiple modules, I am trying to trace the wiring back. In the passenger fuse box, the first 7 fuses (1-7 - top left) plus a few others, are showing 0v to either leg with ignition off, and around 4v with ignition on. A few others are doing the same. Does anybody have an electrical diagram for the tdv8? I am wonder if a link fuse has blown or if the ignition switch is dodgy causing high resistance?

You need to check the voltage whilst the car is running sir! Should show ideally 14.4v then put every electrical device on and see if it holds 14v...

Forgive me if I am missing something obvious but for that I would need the engine to be running! The car wont start. When the ignition is turned on, the solenoid type noise happens as normal, the 2 green dash displays light up but show no information, the gearbox unlocks itself and the parking light flashes red. Nothing else happens! The audio / nav system seems to work on ignition suggesting there is nothing wrong with the ignition switch.
I would like to investigate the electrical supply to these modules, but as I don't have a wiring diagram (I have a copy of the 2002 one but it doesn't look very relevant anymore) I am not really sure what should be happening in the fuse box. What I do know is that the 4V supply I found to 10 or so fuses yesterday seems rather odd. If some of the cars systems run on 4V (which I doubt...) they would surely be fused on the input to the step down supply not the output!

All fuses / fusible links on the passenger fuse board are good.

Fuse 1-7, 31-36 and a couple of others should 'turn on' with the ignition. I have just tested this theory on my dad's L322. Mine are registering 3.8v at the fuses when the ignition is on and 0v when off, possibly suggesting the ignition switch. However the ignition switch consistently turns some parts of the car on in all positions. Could this be ignition switch related?

While testing this I noticed that the brake lights come on with the ignition position on the key (without touching the brake pedal). The brake lights do not work with the key at the accessory position. Could this be something to do with the brake switch?

Sounds like your ABS may have lost its feed/memory? The ABS ECU has so many ECU's dependant on their feed from it...

I was wondering if you ever got to the bottom of your problem with starting, and whether you the diagnostic tool helpful.
I have a problem with some similarities but mine all works after a hard reset and today my replacement switch arrived.

Sorry, I completely forgot to post the solution... Yes I got the issue sorted, it was the ignition switch. Bit of a faff to replace, took about 6 hours to remove and replace the dashboard to get to the switch (switch to the left of the steering wheel) but instantly worked once I reconnected the battery.
The diagnostic tool didn't help, it gave a long list of modules which it couldn't see but that was about it.
Good luck!

Hi - I have the same issues that you had - just wondered how you discovered it was the ignition switch ....... do you have to buy 2 new keys with the switch - then you have separate keys for the doors ? thanks...

I took the passenger compartment fuse board apart and basically followed the issue to the switch. I couldn't find anything else wrong and the symptoms were that of electrical contact breaking down so went with gut feeling.
The switch sits on the back of the ignition, behind the bit that the key goes in so you don't have to replace your key / other locks.
Best of luck, hope you manage to get it sorted.
Ben

thanks so much for the quick reply , much appreciated . My diagnostic checks show issues thrown up by the fault but not clever enough to highlight the ignition switch which is looking like the culprit . I will order a switch and have a go . thanks again , do you have to remove the floor console to get to the ignition switch ?

Last edited by woldsman on 5th Jul 2021 10:04am. Edited 1 time in total