2001 Suburban auto ride compressor deep dive troubleshooting

nvetro · July 12, 2015

I have a 2001 Suburban 1500 LT with the auto ride rear air suspension. On my last trip towing my 22' Hallmark inclosed trailer I noticed the compressor did not kick on when tongue weight was adding which of course caused the rear to sag.

Thinking it had to be the compressor since searching the web focused on the compressor (namely the exhaust solenoid) going bad. I went to CarQuest and picked up a new compressor and installed it and the compressor STILL did not kick on even with tongue weight. I do not have a service ride suspension indicator on my dash (this is likely because I am having a Suburban 2500 dash because I wanted a trans temp gauge and maybe this alert is disabled). I also do not have any codes stored when I used my scan tool.

I applied power and ground to the compressor connector and it ran and applying power to the exhaust solenoid leads on the compressor made it click, thinking MAYBE I got a bad compressor I returned it and got a new one, of course this did not fix my problem. I went a step further and applied power to Pin 30 and Pin 87 of the ALC relay under the hood which should trigger the compressor to go on, this did NOT work and I tested pin 30 was showing 12V just fine and the jump to 87 was working.

Other things I've checked are the IGN3 fuse (inside), Stud #1, and the RDC fuse under the hood, all came up fine. I also tested that there is 12V power at the connector which connects to the compressor (both the 12V main lead and the power lead that goes to the exhaust solenoid. When I stand on my hitch I hear a click coming from the compressor area, which I bet is the exhaust solenoid perhaps.

Anyway, I've checked everything I know and from searching forums. The harness looks in good shape as do the ride height sensors, could I be looking at a bad SCM (Suspension Control Module)? Thats the unit behind the right rear plastic in the trunk. The WEIRD part is when I jump pin 30 and 87 on the ALC relay the compressor doesn't come on, would a bad SCM cause this since I assume power runs through that unit?

Please help :-)

gmtech4 · July 13, 2015

I have a 2001 [/size]Suburban 1500 LT with the auto ride rear air suspension. On my last trip towing my 22' Hallmark inclosed trailer I noticed the compressor did not kick on when tongue weight was adding which of course caused the rear to sag. [/size]

Thinking it had to be the compressor since searching the web focused on the compressor (namely the exhaust solenoid) going bad. I went to CarQuest and picked up a new compressor and installed it and the compressor STILL did not kick on even with tongue weight. I do not have a service ride suspension indicator on my dash (this is likely because I am having a Suburban 2500 dash because I wanted a trans temp gauge and maybe this alert is disabled). I also do not have any codes stored when I used my scan tool.

I applied power and ground to the compressor connector and it ran and applying power to the exhaust solenoid leads on the compressor made it click, thinking MAYBE I got a bad compressor I returned it and got a new one, of course this did not fix my problem. I went a step further and applied power to Pin 30 and Pin 87 of the ALC relay under the hood which should trigger the compressor to go on, this did NOT work and I tested pin 30 was showing 12V just fine and the jump to 87 was working.

Other things I've checked are the IGN3 fuse (inside), Stud #1, and the RDC fuse under the hood, all came up fine. I also tested that there is 12V power at the connector which connects to the compressor (both the 12V main lead and the power lead that goes to the exhaust solenoid. When I stand on my hitch I hear a click coming from the compressor area, which I bet is the exhaust solenoid perhaps.

Anyway, I've checked everything I know and from searching forums. The harness looks in good shape as do the ride height sensors, could I be looking at a bad SCM (Suspension Control Module)? Thats the unit behind the right rear plastic in the trunk. The WEIRD part is when I jump pin 30 and 87 on the ALC relay the compressor doesn't come on, would a bad SCM cause this since I assume power runs through that unit?

Please help :-)

Did you have the truck SCM scanned before guessing anymore ? Hmmmm ?

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nvetro · July 13, 2015

I was trying to avoid bringing the truck to the dealer because I bet al their going to say is bad compressor and change me $200 to tell me something wrong.

Any other DIY things I can test? I'd rather get a new scm on eBay for $125 before throwing money away at the dealer