2003 TD6 with messages coming up , suspension inactive and also HDC inactive at the same time ,, can't put it down to any particular speed or distance traveled , sometimes happens straight away , other times after half hour on motorway ,, when I stop and turn key off then restart it clears it for a while ,, any ideas please

What state is your battery in? (beats stan to it!)

That is the first place to look, check that all your electrics are OK, alternator kicking out a good voltage.

HDC Inactive on startup usually a sign of low voltage.

All the ECUs are in a chain, so a problem in one place may cause others to appear.

Once you are happy that your electrics are OK, further diagnosis is possible.

Do you have an IIDTool (or similar) or access to one? The actual fault codes will help to understand where the issues lie. .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

Battery in good condition , only six months old , checked what I can with electrics , hdc warning isn't on start up ,

Compressor in boot, has it been replaced at any time do you know? Dont think it would affect HDC though, they do tend to eat compressors in my experience

Compressor not been replaced since I've had the car and have no receipt when bought her either ,, suspension works fine when I alter the height ,