Q: Rear Suspension on 2003 GMC Envoy

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The rear air suspension on my car seems to be failing. What is the most likely cause; pump, shocks or air bags and what would the cost be to fix it? Thanks much.
(2) Answers
It is not uncommon for the rear air suspension air pump to fail on your GMC Envoy. That being said, the system should be completely diagnosed buy a qualified technician before any parts are replaced. Most of the parts for the air suspension system are quite expensive. Proper diagnoses of this system is critical to avoid replacing parts that do not correct the problem.
truck is sitting low in the rear used to hear compressor when ever we loaded the truck with any thing,there is another compressor on the truck used for blowing up tires and other things,is this the same compressor that charges the suspension.