Hi

Any ideas guys please....

I refurbed my Hitachi compresor a little while ago as it was throwing "slow to raise errors and sometimes dropping to bump stops while driving".

I tested for leaks first and found none. The car didn't drop at all over two weeks with the battery disconnected and measuring the hub to wheel arch. So I was happy it wasn't a leak.

Refub compressor worked for a couple of days then threw up the suspension light. Never droped though so I carried on driving it for a couple of weeks. Then with driving it slowly got lower and lower as the compressor wasn't coming on at all.

Fitted a new relay first and changed the other air suspension fuses just in case.

Took it to get the codes read at my normal garage. The guy there knows I'll do what I can so he was happy just to plug his machine in. I told him I suspected wiring or something electrical. He said it was low pressure in the reservoir and that it would be a new compressor.
I think its on its original compressor and know they are usually to blame so bought a new compressor.

Fitted it today and still it doesn't fire up.

I haven't a clue where to check for dodgy wires. All the ones I could see I moved incase there was a broken connection to no avail.

So....wondering if there is anythnig else I can diagnose easily myself before I book it in?

The compressor motor wires are easy to follow as they are thick and run from front wheel arch liner down the side.

But first bridge relay contacts to see if it fires up.
Check large fuse first.

Thanks Andy. So remove wheel arch liner?

I've tried a new relay, but will try and bridge the connections. Any advice on what wire to use? I don't want to get fried.

I replaced the J fuse, even though it looked ok, and the 20A and 5A Air Suspension fuses.

Bridge the 2 large terminal holes

If you get a spark the compressors running or trying.

Don’t matter what size wire. Paper clip or something ?

Just run it for 39 seconds max

cheers, will try that tomorrow

I bridged the relay connections but got nothing.

Wiring?

Check continuity between the relay wiring down to the compressor, then you'll know if it is actually getting power.
Further, then give the compressor a 12v direct feed, and see if it fires up. 2011 MY D4 HSE
Previously 2001 D2 TD5, 1996 D1 300Tdi, 1985 90 2.2 petrol.
Bikes! KTM, BMW, British, Classics and others.

WIll do next as I just tried my usual mechanic and he has gone on holiday for 2 weeks!

I'll find some wires I can use to feed a 12v to the compressor, although its brand new, so should be good. Most proably find the old one works too

Any tips on finding the right wires to check continuity for? I saw in another post that they run under the plastic sill. I guess that passenger side and the plastic just above the footplate and not the plastic on the inside between door and carpet?

Failing that, any recommendations of a decent Indy near Gatwick??

they run UNDER the car.

As I think I said there is a large connector behind the front plastic wheel arch liner where 1 thick wire can be seen

check its live there with your bridge in the relay slot.
check the connector there.

you should then be able to kinda follow it or try

Great, thanks Andy

I couldn't see where it went after I got to the reservoir from the compressor. I'll check behind the wheel arch liner.

Maybe a sily question, but... If I give the compressor a direct 12v feed to test, will it raise the suspension? Is it safe to do so in short periods?

I'm just thinking that it might make driving to a garage more bearable, and also I read somewhere that if the reservoir pressure is too low it won't allow the compressor to run? Not sure how true that is.

It might.
If you get the compressor running, start the car straight away and see if it will raise.

Have you had this plugged in at all as yet? a tool that can monitor the solenoids and see what the compressor is actually doing will help here..
If you bridge the relay as mentioned, maybe go to the compressor 12v connector first? Far easier to find than messing with the wheelarch liners straight away. 2011 MY D4 HSE
Previously 2001 D2 TD5, 1996 D1 300Tdi, 1985 90 2.2 petrol.
Bikes! KTM, BMW, British, Classics and others.

Can't see a GAP tool helping much, considing what you have found so far

Given the original diagnosis..Fit a new compressor.. after:-
"Took it to get the codes read at my normal garage. The guy there knows I'll do what I can so he was happy just to plug his machine in. I told him I suspected wiring or something electrical. He said it was low pressure in the reservoir and that it would be a new compressor.

That could be another issue. 2011 MY D4 HSE
Previously 2001 D2 TD5, 1996 D1 300Tdi, 1985 90 2.2 petrol.
Bikes! KTM, BMW, British, Classics and others.

this is what diagnostic machines aren't the only tool required.

A non operating compressor would result in low pressure in the tank, wouldn't it ?