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We have a 2014 VW Golf (diesel automatic) and recently we have started getting sporadic "christmas tree" errors when starting it. A few seconds after starting the engine, we get error after error reported in various systems:

  • parking brake auto-hold
  • ABS
  • anti-skid
  • cruise control

We have seen online, and had it suggested by a mechanic, that the battery may be to blame. I find this hard to understand given that the engine starts fine.

Can anyone explain why it could (even theoretically) be to blame? I can see that this is probably a daisy-chain where one sensor reports an error and this causes other systems to turn off but not why the battery would be the root cause. We're happy if it is, since the other option is an ABS pump problem, but how?

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Some electronics are very susceptible to power differences. Most need continuous power in the ~12-14vdc range to function correctly. The starter, on the other hand, will work at lower voltage levels, with enough torque to turn the engine over and get it started. Once the resting voltage of the battery gets below a certain point, the electronics may start having issues, exhibiting the problems which you are noting while the engine would still be able to start and run. I ran into this very recently on my wife's '08 Hyundai Azera. Once I changed out the battery to a new one, all the symptoms completely went away.

To find out for sure if this is the issue, two things you can do. First, use a multimeter and check the voltage at the battery before you try to start it up in the morning. When I looked at the voltage in my wife's car, I believe it was somewhere in the 10-10.5vdc arena. Second, take the battery to a battery shop or retail outlet where it can be load tested. This can tell you how much reserve capacity the battery has and whether it'd need replaced.

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  • Low voltage during cranking I suspect, if it falls below 9 volts during cranking it will cause this, probably a bad battery or possibly an alternator is not charging it fully.
    – Moab
    Feb 17, 2020 at 17:25

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