Follow up to the Z55 Autoride repair. I found the Denali would sometimes ride smooth and soft and sometimes ride hard? It has very few miles on it since I repaired it, less than 140 so far. I had installed the used pressure switch for the air compressor because the new AC Delco switch that came on this new compressor had been found to not work and was throwing a hard code in my scan tool, since I was getting odd response out of the rear air auto ride system I ordered in a new Dryer since that is the only way I found to get a new pressure switch. It comes mounted on a new dryer. I had time this weekend and checked the pressure parked before starting this repair. Scan tool showed system air pressure was at 76 lbs, 2.4V approx. When driving this Denali with the scan tool connected watching the system air pressure I noticed it slowly leaked, ride would start out very firm with the system showing nearly 80 PSI and as I drove it would slowly drop air pressure till it would get down to zero after maybe 20 minutes of driving? Ride would soften up as pressure dropped? I believe the leak was at the used pressure switch on the dryer. I believe these readings were all bad numbers due to the bad pressure switch/sensor.
I replaced the dryer and switch, had to play with the O ring on the dryer where it plugs into the compressor, the original was pretty loose which could lead to leaks. Got this tightened with a new o ring and assembled.
Tried to test the repaired compressor and it would not come on. Scan tool hooked up to try the exhaust valve, it would not operate? Tried to use the tool to activate the compressor, it would not operate????
I shut the car off, key off and waited about 2 minutes and turned it back on, compressor still did not cycle? At this point I used the scan tool and asked it to clear the codes for just this Z55 suspension system. It did this. As soon as the codes cleared, ( even though the scan tool clearly told me there were no active codes ) the compressor activated normally, pumped up the shocks and shut off. The exhaust valve opens like normal once the shocks went through the initial compressor run and pumped up.
After this I shut down the car, waited 2 minutes and turned the key back on, the exhaust valve opened again and following that the compressor turned on like it should and ran for maybe 30 seconds and shut off.
Compressor is now operating normally/properly. I sprayed the system down with soapy water and watched for bubbles. None showed after 45 minutes.
Checked pressure after the repair in the Z55 system. Now the new pressure sensor is showing the shocks have 23 lbs of pressure. I watched this pressure for an hour to make sure it was not leaking. In the first 5 minutes after the shocks filled on start up the pressure very slowly dropped from 23 PSI to 21.2 PSI. I believe this is just the air balancing out between the two shocks. I did notice the driver side shock fills faster than the passenger side. I believe this is due to the length of air line being longer on the passenger side. After a few minutes the pressure stabilized and stayed at approximately 21.2 for the next hour. Tells me no leaks while parked. I think voltage was .882v V at 21 PSI pressure. I did notice while testing that at 5 v the system shows nearly 200 PSI.
Last test today, took it for a 40 mile test drive, hit the freeway, drove 68 mph on cruise control, 20 miles out, turned around and 20 miles back home. It now drives perfectly, very forgiving ride, takes bumps like a pro. Pressure jumped to 23 psi on the start up for this drive and stayed exactly there the entire drive. I did have a full tank of gas, all seats in the car but I was the only person in the car for this drive. So now I know, an empty 2008 YUKON DENALI has a running air pressure around 23 psi when loaded like mine, basically empty except for the full tank of gas and a driver in the car. I wanted to hook up a trailer with 400 lbs of tongue weight to watch the shocks adjust but ran out of time. No doubt they will work now.
My tool did allow doing a RESET of the Z55 system after repairs. I had read that you should do a Bump Stop reset also after repairs but my scan tool did not offer that option.
I post this information because I could not find any information anywhere telling me what pressure or voltage to expect in a properly working Z55 system.
My scan tool is a Launch X431V+, it offers two way communication with the vehicle. Expensive but it has allowed me to do many projects and find many issues on several cars. It can do some programming of modules, sets TPMS sensors etc. Only downside of this tool it the Updates, updates are free for 2 years after purchase. After that they cost $400 per year and if you do not pay they lock your scan tool. I wish I had bought a tool with lifetime updates provided but this is a very good tool to have in the shop.
Hope this helps the next guy/gal trying to repair a Z55 auto ride system.
Mark
