Help!
it’s a Grand Cmax. Due to it being a modern car all the lights seem to stay on with the doors open.
So ended up with a flat battery. Now the speedo/rev counter and all the buttons on the steering don’t work.

Is this because I jumped it or something else?

Disconnect battery for a while and then reconnect. Might have confused it.

Maybe related to why you needed to jump start it in the first place?

Blown a fuse covering the speedo?

Sounds like something is preventing the body modules from “going to sleep” hence the flat battery? No speedo also shows a lack of communications (CAN BUS) between DIM and the EMS.

Disconnect the battery completely, make sure it’d fully charged, then reconnect and try again (this “hard boot” should reset most issues)

Battery disconnected , put back on .
It only bloody works!
That’s why I love this place.

Ah, it’s good to see the age old solution of turn it and turn it on again has now transferred to cars.

Make sure you are not wearing nylon trousers when you do it.

Nah, you will be fine.

Battery out and on charge over night and then reconnect.

You might need to drive, switch on and off a couple of times. My old Mercedes reported something stupid like 128 errors after a flat battery. Turn it off, turn it on again. 35 faults. Drive two miles and down to 3 faults. Off over night and all clear in the morning.

So what is the correct way to jump a car in the 21st century?

Donor car running, broken car fully off.
Black cable to black cable.
Red to red.
Start car with flat battery.
Spend a while cancelling all the bloody errors.

Read the car manual in case a specific vehicle has specific instructions or terminals.

Trying to jump my car from a neighbours Q7 we couldn’t even see the battery. Had to look in the manual to find its connections. Not making it easy these days.

I managed to fry an alternator by jump starting somebody else’s boat. My advice, run the donor car engine for a few minutes with the car with the flat battery attached via jumpers. Switch off the donor car engine, then try to jump start.This way you are not potentially overloading your alternator.

I was using a jump pack so I wouldn’t think a huge amount of juice was going in.

Jump pack should supply the same voltage and current as anything else, otherwise it wouldn’t work.

When battery voltage goes low, the car becomes like a military academy – bits of it keep passing out*. The gateway then logs a shitload of faults, and some things with faults will be turned off to be on the safe side. Most of then should go away once voltage is restored, or after a short time.

If the Prius battery goes flat (the 12V one) then the automatic driver window wind down doesn’t work for half an hour or so. Just that, everything else is fine.

* prize for recognising that quote

Hitchhikers Guide. 🙂

Probably a good reason for that given other reports in this thread – it does at least weed out the totally incompetent.