How to Solve Air Suspension Issues in the GMC? (Troubleshooting Guide)
In this brief article we will discuss the general issues that occur in the GMC SUVs’ Air Suspension, what the causes are, and Troubleshooting Tips.
Most Common Suspension problems in GMC Air suspension systems
- 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
GMC Air Suspension
We will focus on the 2 major Air Suspension systems that were available as options, in most GMC Trucks, the Z55 and the G67 RPO Codes.
RPO Code Z55
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.
GM Full-Size 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.
RPO Code G67
G67 was offered as an option on the mid-size GM SUV models such as:
2004-2007 Buick Rainier
2006-2007 Chevrolet TrailBlazer SS
2002-2007 GMC Envoy, Envoy XL
2004-2005 GMC Envoy XUV
2002-2004 Oldsmobile Bravada
2005-2007 Saab 9-7X
Unlike with the Z55, the G67 Code air suspension was a lot more simpler with no Adaptive Shock absorbers. The G67 code vehicles came with separate Air Springs and conventional shock absorbers.
A bouncy and rough ride in Yukon Denali AutoRide
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’ in Yukon
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.
Yukon AutoRide sagging 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
Envoy Air Strut failure
- Rear suspension sits low
- Hissing noise from the rear of the vehicle
Troubleshooting Air Strut Failure
- Once the engine starts, the compressor automatically comes on as well and tries to maintain the air pressure that is required for the suspension to function.
- The Hissing noise is basically from a leakage point within the Air circuit. The fact that it is continuous, also gives a clue that it is indeed from the air suspension system.
- The air suspension system tries to maintain pressure all the time. The leakage creates a drop in pressure, which the compressor tries to overcome by overworking.
- The leakage, in a majority of cases, would be located in the Air Springs themselves. Air bellows undergo massive wear and tear.
- Towards the end of the Air bellow’s service life, it develops cracks that would potentially turn into a leakage
- Before removing the air bellow, you will need to depressurize it, so that it becomes saggy to help in the removal.
- Depressurization is done by accessing the air valve in the compressor and bleeding it.
Envoy Air Compressor Failure
- When loading the vehicle, and the rear suspension goes down due to the weight, the Self-Levelling mechanism should automatically start the Air Compressor and increase the Ride Height
- Sometimes, this mechanism does not work, as the Compressor does not come on
Troubleshooting Compressor Issue
- Check the Air suspension Fuses
- Check the Air Compressor Motor Relay
- In the fuse Box located in the engine bay, look for the ECAS fuse and replace concerned Fuses and Relays where necessary.
- If it still does not work, then you need to check whether the compressor is getting power supply.
- Check for voltage after loading the vehicle with 100-200 kgs weight. It should read ~ 12V
- If you find that the supply voltage is not the issue then you need to remove and examine whether the compressor itself might have burned out. Connect a 12V power supply standalone and see if it starts. If not then the compressor needs replacement.
- Before performing a compressor replacement always make sure that the ECAS fuse has been removed. Otherwise the system gets confused the next time you start the vehicle with the new compressor fitted.
Envoy Height Sensor Malfunction
- The rear of the vehicle sags at one corner
Troubleshooting Height Sensor Malfunction
- The rear suspension levelling system is triggered to self-level based on the signal from an electro-mechanical lever mechanism
- The Height sensors have oblong holes on the bracket attachment to the chassis meant for calibration adjustment
- For the Height sensors to activate the leveling mechanism, they need to be adjusted to reference ride height
- The reference ride height is the distance between the chassis frame bottom and the Bump stop bracket on the axle. The reference height is 5.33 inches with +/- 0.1 inch tolerance
- To perform the calibration the frame needs to be raised and supported on stands, and the rear axle needs to be supported on a jack for height adjustment
- The height sensor chassis bolts need to be slightly loosened so as to enable adjustment
- Adjust the chassis height to the earlier mentioned reference height.
- Now tighten the Height sensor chassis bolts
In this brief article we have discussed the general issues that occur in the GMC SUVs’ Air Suspension, what the causes are, and Troubleshooting Tips.