Rear End of Vehicle Sags After Vehicle Sits Overnight (Repair Air Leak In Electronically Controlled Air Suspension (ECAS)

Some customers may comment that the rear end of the vehicle appears to sag after the vehicle sits overnight or longer. After the vehicle is started, the rear end rises to normal operating level.

A 1.5 mm (0.060 in) leak down drop of the rear end over a 24 hour period is considered normal.

An air leak in the ECAS system may cause the rear suspension air springs to lose pressure.

Follow the service procedure below in order to diagnose the cause of the air leak.

Air Leak Diagnosis

Important: Remove the #1 30 amp ECAS fuse from the UBEC before starting the vehicle.

1. Drive or push the vehicle into the service bay and raise the vehicle off of the ground. Refer to the Lifting and Jacking the Vehicle information in the Service Manual.
2. Inspect the rear air springs and document on the repair order which one of the springs is collapsed. The collapsed air spring generally is the circuit that is at fault and is not holding pressure.

Caution: A sudden release of pressure may cause personal injury or damage to the vehicle. The air suspension system is under pressure until the air supply lines are disconnected. Use the following precautions when servicing the air suspension system:

•	Wear gloves, ear protection, and eye protection.

•	Wrap a clean cloth around the air supply lines.

3. Inspect the air lines at the ECAS compressor ferrule nuts for proper installation. Each air line has a bubble 18-22 mm (0.70-0.80 in) from the end of the line that acts like a stop. The bubble should be seated next to the ferrule nut with the line fully seated. If the air line is not fully seated, loosen the ferrule nut and push the line in until the line stops or the bubble is within 2 mm (0.08 in) from the ferrule nut.

Important: Do not over tighten the ferrule nut.

4. Inspect the ferrule nut for the proper torque.

Tighten
Tighten the ferrule nuts to 2.5 N·m (22 lb in).

5. Replace the ECAS compressor, P/N 15006679, if the ferrule nuts are stripped or cross threaded. Refer to the Air Spring Compressor Replacement procedure in the Service Manual.
6. Inspect the ECAS air lines for any kinked or damaged air line from the compressor to the air springs.
7. Replace any damaged or kinked lines using P/N 15324582 (RH) and P/N 15324581 (LH). Refer to the Air Suspension Air Line Replacement procedure in the Service Manual.
8. Inspect the air lines at the air springs for proper line installation. Each air line has a bubble 18-22 mm (0.70-0.80 in) from the end of the line that acts like a stop. The bubble should be seated against the collet on the top of the air spring. When the air line is properly seated, you should not be able to pull the air line out of the air spring without pushing down to release the line from the air spring collet.
9. Seat the air line into the air line collet by pushing the air line into the air spring collet.
10. Replace the air spring, P/N 15159630, if the line will not seat into the collet. Refer to the Air Spring Replacement procedure in the Service Manual.

Important: If very fine scratches are noticed in the air line where it seats into the collet on the air spring, replace both the air line and the air spring.

11. Remove the air lines from the air springs and inspect the lines for very fine scratches in the line where it seats into the collet.
12. Replace the appropriate air line, P/N 15324582 (RH) and P/N 15324581 (LH), and the air spring. Refer to the Air Suspension Air Line Replacement and the Air Spring Replacement procedures in the Service Manual.

Air Leak Diagnosis with Soapy Water

1. Lower the vehicle.
2. Reinstall the #1 30 amp ECAS fuse into the UBEC.
3. Turn the ignition ON and allow the vehicle to rise until the compressor shuts off and the vehicle has reached its normal curb height.
4. Turn the ignition OFF.
5. Remove the #1 30 amp ECAS fuse from the UBEC.
6. Raise the vehicle.
7. Remove the wheelhouse panel on the side that the air spring is deflated. Refer to the Wheelhouse Panel Replacement procedure in the Service Manual. Use soapy water to aid in the diagnosis of the leak area.
8. Spray soapy water on the top of the air spring where the line enters the collet on the air spring and look for bubbles.
9. Spray soapy water on the air lines at the compressor connections and look for bubbles. The bubbles from the soapy water will indicate the leaking area.

ECAS Compressor Output Procedure

Important: Use only the accessory inflator tool assembly that comes with the vehicle. The accessory tool has a built in by pass valve and should be the only tool used to test the compressor output.

1. Reinstall the #1 30 amp ECAS fuse into the UBEC.
2. Open the rear hatch and locate the accessory inflator outlet on the right rear quarter panel.
3. Turn the ignition ON.
4. Install the accessory inflator tool assembly provided with the vehicle.
5. Turn the accessory inflator switch to the on position.

Pressure
The compressor output pressure should be between 138-724 kPa (20-105 psi).

6. Refer to the Air Suspension Diagnostic Information and Procedures in the Service Manual if the compressor is inoperative or out of the output pressure specification.

Parts are currently available from GMSPO.

For vehicles repaired under warranty, use: