For the last couple of days, the driver heated seat hasn’t worked immediately on start up. You switch it on (lights ok) and doesn’t get hot. After some time into the journey, if you switch it off and then back on it seems to work.

I also noticed this morning than neither the driver heated seat, or front and rear screens worked. I initially turned on the seat heater and the defrost program button which. The heated seat started working (switched off and on again) after some time into the journey but the screens had cleared themselves by then so not sure if they also started working or not.

Are these circuits linked in any way? The fact that the seat heater does work some time into the journey makes me wonder if it’s a current fault – in other words it takes time before there is enough juice to run all these power intensive circuits at the same time?

Any thoughts?

That is a symptom of a battery issue. The car will automatically prevent systems from working if they would excessively drain the battery. There is a hierarchy of systems that are shut down. Could be the sign of a tired alternator or battery. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Thanks - that makes sense. Do you know what that hierarchy is?

As below. When cold, for example, the system will reduce power to the air suspension, then the front seats etc., then inhibit the front seat heaters and so on. Hopefully this makes sense.

Quote:

Cold Start Electrical Load Management

Power Reduction / Inhibited
1 / - Air suspension
2 / - Front seat heaters
3 / - Entertainment system
- / 4 Front seat heaters
5 / - Rear window heater
6 / - Windshield washer jet and exterior mirror heaters
- / 7 Windshield washer jet and exterior mirror heaters
8 / - Windshield heater
9 / - Climate control blower
- / 10 Rear window heater
- / 11 Windshield heater

Hot Start Electrical Load Management

Power Reduction / Inhibited
- / 1 Front seat heaters; windshield washer jet and exterior mirror heaters
2 / - Windshield heater
3 / - Rear window heater
4 / - Air suspension
5 / - Entertainment system
- / 6 Windshield heater
- / 7 Rear window heater

Continuous Electrical Load Management

Power Reduction / Inhibited
- / 1 Front seat heaters
2 / - Windshield heater
3 / - Rear window heater
4 / - Air suspension
5 / - Entertainment system

Quote:

The ATC module calculates the electrical load from the battery voltage and generator output voltage, and compares the result
against the maximum load available from the generator. The calculation is averaged across the first 20 seconds after the engine
starts, and subsequently averaged every 60 seconds. When the ignition is turned off, the ATC module stores the status of the
electrical load management for 20 seconds. If the engine is re-started within the 20 seconds, the ATC module resumes electrical
load management using the stored status. If the engine is re-started after the 20 seconds, the timers are reset and the ATC
module re-calculates the status.

If the electrical load is more than the maximum load available, the ATC module requests an increase of engine idle speed using
the medium speed CAN bus message to the ECM. If an electrical load imbalance remains after an increase in engine idle speed, or
if the electrical load is more than the capacity of the charging system, the ATC module reduces the electrical load by reducing the
power of some vehicle systems or inhibiting their operation. The number of systems controlled depends on the electrical load
reduction required. The systems controlled, and the order in which their power is reduced or they are inhibited, are contained in
three priority tables. The table used depends on the ambient air temperature, battery temperature and ECT:

The cold start table is used when the ambient air temperature is less than 5 °C (41 °F) and the ECT is less than 30 °C (86
°F).
The hot start table is used when the ambient air temperature is 5 °C (41 °F) or more and the ECT is less than 30 °C (86
°F).
The continuous table is used when battery temperature is more than 5 °C (41 °F) and the ECT is more than 50 °C (122
°F).
If none of above conditions are met, the ATC module adopts the last used table

Splendid - that is extremely helpful. I'll test the battery and alternator output and see whats what.