How to Fix Suspension Issues in the GM 755? (3+ Troubleshooting Tips)
In this brief article, we are going to discuss the issues that occur in the GM Z55 AutoRide Air Suspension, what the causes are, and Troubleshooting Tips.
Top 3 Rear Suspension problems in GM Z55
- A bouncy and rough ride
- A dash warning light of ‘Service Autoride’ or ‘Service Ride Control’
- Vehicle saging at one axle or at just one corner
What is the GM Z55 Suspension?
The Autoride, also known as RPO Code Z55, is GM’s trademark name for their own unique automatic pneumatic load-leveling suspension and computer controlled Adjustable Shock Absorbers. The Autoride system provides for the best balance between a great ride and sharp handling characteristics.
Many GM SUV’s were offered with an optional Z55 suspension package on the Chevrolet Suburban, Tahoe, Avalanche, among other GM trucks produced from the 2000 to 2014 model years.
The Z55 Package was also available as a standard on the
- GMC Yukon Denali and
- Yukon XL Denali trim levels and is available
On GM’s upmarket SUV models like the Cadillac Escalade, and Escalade EXT, this system retained the Z55 option code, but was named differently as “The Road Sensing Suspension” instead of Autoride.
The Z55 Autoride system has:
- Dynamic damping modes, and
- Automatic load control via an air suspension system
to maintain the Suspension Ride Height and maintain ride quality both when the truck is empty and when it is fully loaded with cargo or passengers. Hence, the Z55 Autoride system is a hybrid of a dynamic hydraulic and an air suspension.
- The GM AutoRide Adaptive Suspension works via a centrally-located air pump.
- When necessary, it pumps air into each shock absorber to raise the vehicle, or pumps air out to lower the vehicle.
- The system works in conjunction with an independent multilink rear (Coil Sprung) suspension system as well as MagnaRide Shock Absorbers.
A bouncy and rough ride in Yukon Denali
The Major Symptoms of Rear Rattling Noise Issue are:
- A noticeably harsher ride quality
- Compressor not starting at all
Root Causes for bouncy and rough ride
There are two Major Potential Causes for a Bouncy and Rough Ride :
- Air Compressor Malfunction
- Air Leakage in the System
Troubleshooting bouncy and rough ride: Air Compressor Malfunction
Ideally, within 5 secs of starting the engine, the Compressor must turn on. You will notice it by the distinct compressor sound. If this does not happen then you need to do the following:
- The first thing to check would be the Fuses; they are located under the hood in a box on the right side
- Use a Multimeter to check for continuity in the AutoRide related fuses as shown below
- Replace any of the fuses that may have blown. Restart the car and see if the Compressor turns on. If not, then the next thing to check is the ALC Relay.
Check ALC Relay
- Check the Automatic Level Control (ALC) Relay, which is located right below the Fuse Box. Bypass this relay using 1-square wire and check whether you can hear the Air Compressor start running. If not, then it means the Air Compressor has died
Inspect Air Compressor
- Disconnect the Air Compressor and remove it for inspection. The Air Compressor is located at the Rear end of the vehicle on the Driver’s side
- Supply direct Battery power and see if the compressor starts
If it does not, then replace the Compressor and repeat the Direct supply test. Fit onto the vehicle once verified.
- Even if you have rectified a possible Compressor problem by the appropriate replacements, you must understand that compressor failures usually happen due to overwork. And over work happens when there is a pressure drop in the system due to leakage/s.
- Hence it is highly essential to check for system leakages even after you see that the compressor seems to be working fine.
Troubleshooting Bouncy and Rough Ride: Air Leakage
- Air Leakages have to be checked using a Soap Bubble Test
- To conduct this test you need to first pressurize the system. Start the vehicle and let the air compressor run for at least 10 min.
- While the engine is still running, First check the Air Bellows by spraying soapy water all over.
- Check if there are any spots that are bubbling. To see this, you can wipe off the foam and see if the bubbles form again on their own without you spraying any more soapy water.
- Repeat the same procedure all along the air lines, especially at those locations where there is a connection or joint
A dash warning light of ‘Service Autoride’ or ‘Service Ride Control’
Probable Root Causes for AutoRide Warning message
The most probable Root causes for the ‘Service AutoRide’ Warning message are:
- Compressor needs reset
- Air Compressor Malfunction
- Air Leakage in the System
Troubleshooting AutoRide Warning message: System Reset
- Sometimes the system could have gone out of calibration due to road bumps
- You can try resetting the compressor by disconnecting the battery and keeping it that way to 15 mins
- If a ‘Reset’ did not work then try troubleshooting the Compressor and the Air Bellows.
Troubleshooting AutoRide Warning message: Compressor and Leakage
For troubleshooting tips on Air Compressor malfunction and Air Leakage refer to this section.
Vehicle saging at one axle or at just one corner
The vehicle seems to be sitting lower on one corner or one side. If you measure, with a tape, the height of the wheel center from the fender bottom, all 4 corners, you notice there is a significant difference of at least 1 inch.
Root Cause for Sagging problem
- Usually, the reason would be related to the sensor calibration. For some reason, maybe due to a hard bump from the road, the height sensor would have lost its reference ‘zero’ position.
- Another reason could be that one particular Air Spring has a leak or has gone weak due to age
Troubleshooting Sagging Problem
- ‘RESET’ the suspension by following the steps explained in this section.
- If Reset did not work, you can now check whether the Height Sensor Linkages are still intact and that they have not broken
- Once you see that the Height Sensor Linkages are all proper, you can now check whether the electronics part of the sensors are in working condition.
- Using the diagnostic tool you could troubleshoot by plugging the diagnostic tool to your OBD II port. Go to the ‘Electronic Suspension Control’ ->And ‘Read Data Stream’. Here you can select individually, each of the sensors that you want to diagnose. They will be named as “RR Position Sensor”, “RF Position Sensor”, etc.
- Now raise or lower the suspension and see what happens to the value shown in your position sensor; if it works, then it will change as and when the suspension ride height changes.
- If you find that all is good up until this point, the only thing left is to check for leakages in the Air Spring that has a sag. You can use Soapy Water Spray and do a Bubble Test
In this brief article we have discussed the issues that occur in the GM Z55 AutoRide Air Suspension, what the causes are, and Troubleshooting Tips.