In an effort to increase your air ride system knowledge, here are the top questions (and answers) from a recent ImportCar webinar on air ride diagnostics.
1. The compressor does not run when the car is parked. What is the problem?
Most modern air compressors do not directly fill the air shocks or struts. In most systems, the compressor fills a reservoir (with some Lexus models being the exception), and the air in the reservoir is then used to trim the pressure in the air ride units. When the reservoir is depleted, the system turns on the compressor. But, the compressor will turn on for only short periods if the vehicle is stationary. The compressor will turn on when the vehicle is at speed so there is airflow and less of a chance of the driver hearing the compressor operate.
2. The car has multiple communication codes. How can this prevent the air ride system from working?
A simple failure of a trunk switch, BCM or security module can cause the system to be inoperative on some vehicles. Why is that? Late-model air ride systems are on the serial data bus so they can share information. They can use different inputs from other systems to determine the correct position of the suspension, which can include vehicle speed, engine load and other PIDs. Likewise, the air ride module shares data with the other modules on the serial data bus.
3. What is happening when an air ride system is in a fault or service mode?
When a system is in fail-safe or fault mode, it is trying to preserve the system until it can be serviced. This means that the control module will not allow the compressor to melt down if there is a leak. In addition, most units will maintain minimum pressure or height in order to prevent a bladder from fully compressing and the suspension from bottoming out.
4. The system says it is missing the input for the ambient air temperature. Why does this matter?
Most systems factor in the ambient temperature. The outside temperature can affect compressor runtime because of the relationship between temperature to air density. Some systems might use the temperature sensor mounted on the front of the car for the HVAC system, while others use the engine’s mass airflow sensor. Check for communication codes in the HVAC module.
5. The system has a code for reservoir plausibility and/or the compressor has timed out. Does this indicate a leak?
It could be a sign that the compressor is worn out, even though the vehicle is still maintaining a minimal or normal ride height. That’s because all air ride systems are unable to do two things. First, they can’t measure wear in the compressor. As a compressor runs, the ring wears and the compressor is unable to generate enough pressure to operate the system. The control module can’t measure the wear on the ring. Second, an air ride system can’t detect leaks in the system. But, it knows that a healthy compressor will generate a specific change in pressure in the reservoir over a specific amount of runtime. The plausibility and timed out codes are set because the amount of pressure generated did not match the system’s expectations.
6. How and when should an air ride system be calibrated?
Before a vehicle is returned to a customer after a strut unit or sensor is replaced, you should perform a calibration procedure for the air ride system. Calibration procedures typically involve measuring ride height at all four corners and entering the data into the scan tool. Not doing this can lead to possible codes and, in some cases, strange alignment readings for cross camber and toe angles.
7. What is the best source of information on air ride?
The key to understanding the embedded logic of air ride systems is service information. For most vehicles, the air ride logic is included in the “system description and operation” section of the service information. Some OEMs include diagnostic tests in the service information that can pinpoint faults.
8. What types of scan tools can work with air ride systems?
Scan tools are essential for working on some systems. Some enhanced scan tools can even observe PIDs for the air ride system like valve operation, modes and vehicle position. The next-level tool can perform bidirectional tests and possibly perform a calibration of the system. There are non-factory tools that can perform these tasks.
9. What is the future of air ride?
Air ride is not going away and system features are constantly improving. For example, the size of the inlet and dump valves on the new air ride systems for Mercedes-Benz and BMW are increasing. These valves are what allow the suspension to react in 60 milliseconds. Also, dual chambers in the air bags allow the pressure to be managed more effectively and reduce compressor runtime.