Strange electrical issue C5 Exclusive

Hi community,

I am having some trouble working out an electrical fault with my car. After receiving it back from the garage after having both head gaskets replaced, they advised my battery was ‘shot’.

Upon trying to turn the car over while leaving, nothing. Classic symptoms of a bad battery so got jump started to leave.

After attaching a new battery and turning over the engine, after my first key click all the normal dashboard icons and startups commence, once I turn the key further to start it everything just dies. The only indication I have of power is my central locking light flashing. Everything else is dead electrically including locking the car, lights etc.

Thinking it was a faulty battery I replaced it with a second new one, same thing. Everything is just dead.

Strangely though when I jump start the car everything turns over as normal, I can drive the car any amount of mileage with no issues at all. I can even lock and unlock the car as normal, until I turn over the engine like above and everything dies.

I’m unsure what could be the fault here, if it had of been the starter and alternator they shouldn’t work when being jumped? If it had of been the battery it’s extremely unlikely I have two faulty brand new batteries, all the terminals look tight and corrosion free.

Any help or suggestions would be appreciated!

Thank you.

Classic symptom of loose and/or dirty connections.

Did you clean them with a wire brush ? both surfaces ? make them nice and shiny.


I did some work and had my starter out for 10 days. And no start. Cleaned connectors on cables and it started fine. A little corrosion can do that.

also check for an engine ground wire not being reconnected.


You have to analyze what is different when hooking jumper cables up? You are connecting directly to the cables. Post to cable connector is suspect.

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First guess is as posted above, corroded/loose battery connectors. If not that, second guess, it’s possible some of the computer’s “start” electronics were damaged by jump starting. It’s also possible the electronics damage occurred as part of the head gasket job, esp if you had no start/cranking problems prior. Askyou shop to double check all the chassis grounds have been properly reconnected, especially those from the battery negative, from the engine, and from the transmission.

Thanks for all your post, I will start to diagnose this tomorrow and keep you all updated.

Thank you.

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Looks can be deceiving. After being 100% the battery connectors had no corrosion on them, I cleaned them up anyway and just like that, the car starts as normal everytime.

Thank you for your reply’s and showing me I was wrong!


A resistive oxide layer can form on metal surfaces, which is nearly impossible to see. More common on aluminum, but possible on other metals too presumably. Glad you got your C5 back to reliably starting. Just curious, are you located in Ireland?