During a 12 days trip abroad, the car stayed in an open air parking lot at what we would call normal temperatures here (5°C to 25°C). When we came back, the car started normally, but all sorts of messages appeared: hill descent control disabled, ABS not available, drive with caution, etc. When switched into drive, it just started rolling and I almost couldn't brake! The pedal was incredibly hard to press! I stopped the car, waited, restarted it, same thing, impossible to drive. The parking owner came and asked what’s going on. He said that he used to own a Range Rover a few years ago and he found himself in a similar situation, in the middle of nowhere, without access to recovery so he called his dealer and the engineer reluctantly told him to disconnect the battery and to wait a minute, then to reconnect it... He said that this solved the problem, so he brought a wrench, we disconnected the battery and to my surprise it did solve the braking problem! Apparently a reset helps with this... I should mention that I tried to use the Autel OBD tool, but it couldn't erase the errors...

Last edited by adara on 2nd Jan 2023 6:43pm. Edited 2 times in total

Don't know much about the PHEV but that sounds like the 12v battery has died enough to cause multiple errors, not unusual at airports as all the electrical signals floating around can wake the car up multiple times a day, each time depleting the battery somewhat...

Battery disconnection and reset usually sorts it, just get the battery and 12v charging system checked out..  Pete

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2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Parchment over Navy Interior. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand, Jet Interior. Sold
2002 L322 Vogue 4.4 V8 Epson Green, Ivory over Aspen Interior (Fatty Offroader) Sold
-Click for Project Fatty off roader-

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Don't know much about the PHEV but that sounds like the 12v battery has died enough to cause multiple errors, not unusual at airports as all the electrical signals floating around can wake the car up multiple times a day, each time depleting the battery somewhat...

Another trip, another 10 days in which the car remained unused, this time in the garage, same behavior: no brake servo and the messages: OK to drive with caution, ABS not available, HDC not available.
But, disconnecting the battery didn't help this time... So I went to the dealer and they said both batteries need replacing, the 90 Ah one and the 14 Ah auxiliary one... Price at the dealership £330 and £240 respectively, without labour...
The price in specialized stores is £160 pounds (Varta, identical to the JLR labeled one) and £52 (Exide, also identical), available tomorrow. They reluctantly agreed to let me bring them, will see the fitting cost tomorrow & also if this solves the problem...

Last edited by adara on 2nd Jan 2023 6:44pm. Edited 2 times in total

Phew, the problem was solved. The batteries were indeed the cause and especially the auxiliary battery, completely gone, 0 volts... I would’ve imagined that the failure of a battery would generate start up problems, warning messages, but not braking failure!!! £245 for diag and replacement were added to the cost of the batteries...

Last edited by adara on 2nd Jan 2023 6:45pm. Edited 2 times in total

Interesting fault, I never really give the aux battery any thoughts. You would think the system would be clever enough to give you a warning

" Attention your Aux battery is failing this could result in Death, as your brakes fail!!!!"  2018 SE SDV8 4.4 Byron Blue

Precisely. There were no warnings of any kind, there were no starting problems, but it’s true that 99% of the time the car starts in electric mode (PHEV)…