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Hi all,

After leaving work today my car started to play up. After turning the ignition key the engine would start for about 2 seconds then cut out. The immobilizer light on the dash flashed a bit pointing to an immobilizer fault. After I tried it 3 times it started and ran fine. I got home and plugged Vag-com onto it and got the following fault code:

17978 - Engine Start Blocked by Immobilizer
P1540 - 36-11 - - - Intermittent

I checked the state of the battery and it was about 11.9 Volts so it needs replacing. Would a duff battery cause a fault like the above???


(Not sure where to put this post so i've put it in electrical aswell. If this was wrong i'm sry)

It's possible a low battery might cause that, but more likely a bad connection between the immobilizer and the reader coil. Check your immobilizer for fault codes too. What year is this S4?

-Uwe-

I think this is a common problem on all A4's, maybe the ignition lock ( the bit you put the key into). I am sure I have read about it somewhere.

Cheers for your help lads, Its a 2000 S4, I'll have to check the immobilizer fault codes as I haven't done that yet. I'm going to get a new battery the weekend so hopefully that will be the fix. If not i'll have a look around the web for people who have had similar problems.

By the way Uwe I have only had Vag-com for a few weeks and what a top bit of kit, well worth the cash, Ross-Tech rule!!!

Cheers Phil

Right then just plugged it back into Vag-com and this is what came up:

Instruments

1 Fault Found:
01176 - Key
07-10 - Signal too Low - Intermittent

Address 25: Immobilizer
Part No: Bit teA dre ss
Component: e 17 eingeben

No Faults Found

or DTCs not supported by controller
or a communication error occurred

For some reason it wouldn't read the immobilizer module.....
Could the battery in the keyfob be low??? I think i'll change it just to make sure.

battery in the key fob is just for the remote lockng and alarm, that's a seperate system to the immobilisor which is a transponder in the front part of the key which doesn't require battery power

There is no separate immobilizer module in that car. "Bitte Adresse 17 eingeben" means "Please use address 17" (the instrument cluster). Sort of like the girl with the tatoo on her backside that says "Please use other door"..

Intermittent "Key -- Signal too low" codes are a classic symptom of dogdy connections between the immo (part of the cluster) and the reader coil at the ignition lock. You should unplug whatever connections are between on that particular car, clean connections with an appropriate contact cleaner, apply some contact stabilizer, and replug. Chances are you'll be good to go for several more years.

-Uwe-

Cheers for that Lads i'll have to brush up on my German!! I'll have a go at that the weekend and let you know how I get on.

Just a quick update. I've changed the battery and the fault codes have not reappeared, so all is good for now.

Cheers Phil