I know renting the scanning tool doesn't seem great; but, it's the easiest way to start diagnosing the problem.
I have had the Xineering GM Shock Sim resistors for over 50k miles now. Yes, there have been some failures that have been good learning experiences for me. Initial install (at local auto shop) saw the resistors get a voltage spike which fried one of the ride heights. Xineering sent me a new ride height resistor. I also think that this local auto shop broke the small plastic locking clips on several of the ride height sensors, which makes the connection between sensor and Xineering resistor not 100% solid. I've gone ahead and electrical taped around the plugged in components. I think winter weather (snow and salt and gunk) here in Maine played a role in another resistor failing. Xineering again replaced that one.
Most recently, I've been throwing a RR Ride Height Sensor code. Not always, just from time to time. Using Xineering's scan tool, and a volt meter, I was able to determine that the RR Ride Height Sensor is shot. I literally had to manufacture a new sensor rod to "hold" the sensor in a good position. Using the scan tool, I was able to read the voltages going to the RR Ride Height sensor. As I moved the sensor arm up and down I saw the voltages going up and down. Once around 2.4 volts, I cut my rod and installed. For reference, the sensor arm is now about 1 inch higher than where it should be, but I'm getting proper voltage.
Why is voltage important? The Xineering Shock Sims product rely on proper voltage to function. This is one reason why the ride height trim procedure is recommended by the company upon installation of the product. This reprograms the computer with the new ride height, but also stores the values associated with the ride height sensors.
This leads to the BIG update. I haven't seen anyone talking about it here on the TYForum, but I have been Beta testing for about 9 months now. Super impressed! Xineering's new
OBDSS product is better performing, easier to install and maintain, and works great!
http://www.shocksims.com/obdss.html
This new product accomplishes the same MRC delete on our GM trucks and SUVs without using ride height or shock simulator resistors. This means that the 8 resistors on the exterior of the vehicle (plugged in underneath) are moved inside and live under the dash, plugged right in to the OBDII port. The OBDSS requires proper voltages at all 4 corners, so your OE sensors need to be functioning properly. Xineering has some neat protective plugs you can also install to keep your sensor clean from road debris. I have been really happy with how this new product has performed. I am using an OBDII splitter also, so there is an option to have the Xineeering shock sims running as well as another product (ie: AFM delete maybe)
Safe Travels!