Hello all, thanks in advance for any help.

I have a 2006 ls430 with the UL package. Like most guys, i've ended up doing a lot of work to keep the OEM air suspension functional. So far I have replaced the compressor, 3 out 4 bags (both rears), and the exhaust solenoid on the compressor assembly. I'm now experiencing a weird issue where the rear bags will randomly deflate, and i will get the code C1751 "continuous current to compressor motor". Using techstream, I can clear the code and the rear end will come back up for a while. I can also use techstream to manually bring the bags back up. It used to be I would have to do that every once in a while, but now the code comes back after only a few minutes. I checked both rear height sensors and they are functioning properly. As far as I can tell from techstream, all the other various sensors appear to be functioning. Where should I look next to identify the issue?

 

Rear valve block. It controls the air in and out of the struts and when the seals go, you get weird behaviour like this.
48096-50040 VALVE SUB-ASSY, HEIGHT CONTROL, NO.2

 

Thank you my good sir!

 

Got the new part in and installed it and was able to get the car to lift back up after an hour or so. Took a look at it this morning and the car has started to fall in the rear again. Could it be the line going into the rear valve block has a small leak in it? Thanks for the help by the way!

 

It could. Did both sides drop the same amount overnight?
If one side drops further than the other, it is possible that the struts themselves are both leaking.

With a brand new valve block the seals should not be allowing any air out of the struts, so once up they should stay there.
Did you fit a brand new block or a used one?

 

The right side dropped a little lower than the left. It is also worth noting that another 24 hours after the rears had dropped, the front right also lost some pressure. As for the valve block, I ordered a supposedly new OEM block from a Japanese based parts seller on eBay. The struts I also purchased off of ebay, and i believe they are remanufactured. In retrospect I should have just bought some aftermarket struts. I wouldn't doubt that the struts I bought are already shot, but I would be more inclined to believe it's a single failure point since they failed at the same time.

If the system was functioning correctly, with the car off, would a valve inside the rear block prevent pressure from escaping the struts or would that be a valve further upstream?

 

My understanding of the system is that the compressor provides pressure to the reservoir which in turn provides pressure to the front and rear valve blocks.
The valve blocks control the air flow to and from the struts under computer control, so they are what regulates the pressure in each shock.

A new valve block should prevent a strut from losing pressure, unless there is a leak in the strut or a leak in the hose/connections between the block and the strut.
If the struts are dropping at different rates, I would suspect the struts/connections/hoses. Don't forget to check for leaks at the connections with some soapy water.