I live in the land of speed bumps and road construction. The last couple of days my 05 S Type had started acting up in a weird way. When I;m driving everything is fine, but any bump like a speed bump or different levels of pavement all the electrical processes go out for 2 seconds or so. The dashboard and all other displays go dark and the AC stops. The doors unlock too. Once the power comes back on theres a distinct "clunk" and the car shudders a little. At this point I get three new codes flashing: ABS fault, Gearbox fault and DSC fault. Everything seems ok except when I pull out from a stop it seems to be in a higher range gear and takes forever to get going.
When I stop the car, put it in park, turn off the ignition and restart the car it all goes back to normal... until I hit another bump.
I have some theories but would like to hear from you experts as well

 

Based on your description, this appears to be another battery-related issue.

How old is the battery and what is the voltage reading? If it is still the original one, replace it and if it displays less than 12.5 volts with the engine off, replace it.

Have you checked all the connections at the battery terminals and earth points for tightness or corrosion?

 

I would concur on the connection diagnosis.

 

The doors unlocking is a giveaway it's probably related to the inertia switch in some way. Possibly corrosion at the switch or in the circuit between it and the ignition switch. Inertia switch is at the lower LH "A" post.

Good luck!

 

The battery is only six months old. I checked the connections but not the voltage
I will check the intertia switch as well. Thankd everyone