[77newell]

If air pressure is maintained on the dash or rear gauge while shut down with the rear actively sagging then the only valve that can cause the leak down of the bags is the "down" solenoid which you should be able to detect with soap bubbles over the vent on the 6-pack. A leaky "up" solenoid would cause an increase in height as long as pressure in the service tank is higher than bag pressure. The HCV solenoid if leaking should allow only a limited decrease in height until the HCV tries to raise the coach. In this last case, it will stop the drop until leaks in the supply air to the HCV goes below that needed to raise the coach and then those air leaks will cause the coach to drop.

So, noticing the timing of the drop after the key is shut off will help you diagnose where to look for the problem. If it is immediate, then the first defect noted above is more likely, if there is a delay until the service tank pressure drops it could be the later defects noted above.

Air consumption while driving is also a hint at where to look. A leaky HCV solenoid will cause no problems on the road, but can cause problems when parked. If an air bag is leaking you will see higher air consumption on the road. A leaky "down" solenoid will increase air consumption on the road, symptoms similar to a leaky air bag.