Volvo XC90 air suspension / SUM calibration issue

[liushaohuai5]

Hi everyone,
I’m trying to troubleshoot an air suspension calibration issue on my 2016 Volvo XC90 T8 and would appreciate some advice from people familiar with VIDA/SUM calibration.
Background:
The left rear height sensor linkage was previously disconnected from the sensor arm. Before I fully restored the mechanical position of the linkage and sensor arm, I performed a calibration in VIDA while the vehicle was physically sitting at what looked like normal ride height.
At that time, the sensor readings were roughly:

• Left rear: 0.55 V
  
• Right rear: 3.23 V
  

The car was physically at normal rear ride height, but the left rear sensor was clearly near the end of its voltage range because the linkage/sensor arm was not in the correct mechanical zero position.
I have now restored the left rear linkage and sensor arm position. At the same physical normal ride height, the rear sensor readings are now approximately:

• Left rear: 3.23 V
  
• Right rear: 3.23 V
  

The sensor behavior also seems mechanically reasonable now. When the rear suspension rises, I observed:

• Left rear voltage decreases, for example 3.3 V → 1.9 V
  
• Right rear voltage increases, for example 3.3 V → 4.5 V
  

So I assume the rear sensors are mirror-oriented and opposite voltage direction left vs right is normal.
The problem:
Even though the car is currently sitting at normal physical rear height, when I command “normal level” / enable leveling, the rear suspension still rises. My suspicion is that the SUM still has the previous bad calibration stored, where it learned that 0.55 V on the left rear sensor = normal ride height. Now that the left rear sensor is mechanically restored to about 3.23 V at the same physical height, the SUM may interpret the car as too low and tries to raise the rear until the left rear voltage moves back toward the old incorrect reference.
My questions:

1. Does this interpretation make sense? In other words, could the SUM be chasing the old left rear calibration value of ~0.55 V even though the mechanical sensor position has now been corrected?
   
2. Is there a Orbit procedure that allows a static height / sensor position calibration where I can keep the car at the current correct physical ride height, enter the measured heights, and overwrite the old calibration?
   
3. If the calibration routine first tries to auto-level using the old calibration, is it safe/reasonable to temporarily disable the compressor or remove the compressor fuse so the rear cannot be raised during calibration? I understand that residual reservoir pressure could still raise the car through the valve block, so I’m not sure whether this is a valid approach.
   
4. Does VIDA require the compressor / air suspension system to be fully online for SUM calibration to complete, or can the height sensor calibration be written with leveling disabled?
   
5. Is there any SUM adaptation reset, initialization, “identification,” software reload, or re-programming procedure that clears an incorrect height calibration? I do not mean just clearing DTCs, but actually resetting/relearning the SUM height reference.
   

I’m trying to avoid calibrating the car after it has already been incorrectly raised by the old calibration, because that seems like it would write another bad reference. My goal is to keep the vehicle at the current correct physical normal height and overwrite the old SUM calibration with the corrected sensor positions.
Any advice on the correct calibration sequence or safe procedure would be appreciated.

[liushaohuai5]

Hi everyone,
I’m trying to troubleshoot an air suspension calibration issue on my 2016 Volvo XC90 T8 and would appreciate some advice from people familiar with VIDA/SUM calibration.
Background:
The left rear height sensor linkage was previously disconnected from the sensor arm. Before I fully restored the mechanical position of the linkage and sensor arm, I performed a calibration in VIDA while the vehicle was physically sitting at what looked like normal ride height.
At that time, the sensor readings were roughly:

• Left rear: 0.55 V
  
• Right rear: 3.23 V
  

The car was physically at normal rear ride height, but the left rear sensor was clearly near the end of its voltage range because the linkage/sensor arm was not in the correct mechanical zero position.
I have now restored the left rear linkage and sensor arm position. At the same physical normal ride height, the rear sensor readings are now approximately:

• Left rear: 3.23 V
  
• Right rear: 3.23 V
  

The sensor behavior also seems mechanically reasonable now. When the rear suspension rises, I observed:

• Left rear voltage decreases, for example 3.3 V → 1.9 V
  
• Right rear voltage increases, for example 3.3 V → 4.5 V
  

So I assume the rear sensors are mirror-oriented and opposite voltage direction left vs right is normal.
The problem:
Even though the car is currently sitting at normal physical rear height, when I command “normal level” / enable leveling, the rear suspension still rises. My suspicion is that the SUM still has the previous bad calibration stored, where it learned that 0.55 V on the left rear sensor = normal ride height. Now that the left rear sensor is mechanically restored to about 3.23 V at the same physical height, the SUM may interpret the car as too low and tries to raise the rear until the left rear voltage moves back toward the old incorrect reference.
My questions:

1. Does this interpretation make sense? In other words, could the SUM be chasing the old left rear calibration value of ~0.55 V even though the mechanical sensor position has now been corrected?
   
2. Is there a Orbit procedure that allows a static height / sensor position calibration where I can keep the car at the current correct physical ride height, enter the measured heights, and overwrite the old calibration?
   
3. If the calibration routine first tries to auto-level using the old calibration, is it safe/reasonable to temporarily disable the compressor or remove the compressor fuse so the rear cannot be raised during calibration? I understand that residual reservoir pressure could still raise the car through the valve block, so I’m not sure whether this is a valid approach.
   
4. Does VIDA require the compressor / air suspension system to be fully online for SUM calibration to complete, or can the height sensor calibration be written with leveling disabled?
   
5. Is there any SUM adaptation reset, initialization, “identification,” software reload, or re-programming procedure that clears an incorrect height calibration? I do not mean just clearing DTCs, but actually resetting/relearning the SUM height reference.
   

I’m trying to avoid calibrating the car after it has already been incorrectly raised by the old calibration, because that seems like it would write another bad reference. My goal is to keep the vehicle at the current correct physical normal height and overwrite the old SUM calibration with the corrected sensor positions.
Any advice on the correct calibration sequence or safe procedure would be appreciated.

Can anyone tell me if Orbit will do normal leveling during the calibration? The current setpoint is wrong so using VIDA will raise the rear up.

[konrado1]

Hey, You don’t actually need to open VIDA to check if your sensor values have stabilized. You can monitor everything directly inside OrBit before doing the calibration!Here is exactly what you need to do to verify the system: In OrBit, go to the third tab: ECU Tools.In the top-left corner, under Active Diag ECU, select the SUM (Suspension Module) from the list.Make sure the request Type is set to Read Data by ID (0x22).Use the filter to select and monitor the following sensors:Front Left (FL) Height SensorFront Right (FR) Height SensorRear Left (RL) Height Sensor (the one you just fixed!)Rear Right (RR) Height SensorBody Acceleration Sensors (Front and Rear)Click the Parameters Monitor button at the bottom. What you need to look for:Observe the live readings while the car is stationary on flat ground:The values must be completely steady. You should see a flat line on the graph with no voltage fluctuations or sudden spikes.This will confirm that your repaired Rear Left sensor—along with the other three corners and the acceleration sensors—is sending a clean, reliable, and noise-free signal to the computer.Once you see that all four corners and acceleration sensors are steady and stable:You can safely close this monitor, go to the Service tab, and run the Air Susp. Calibrate routine. OrBit will override the old 0.55V error, level the car properly, and successfully save the new ride height reference!