The air ride suspension on Land Rover Range Rover and Discovery models is what helps set these vehicles apart from a normal SUV. The system lifts the suspension up over obstacles, and lowers the suspension to make it easier for the occupants to get in and out. But with functionality, comes complexity.
Late-model Range Rover and Discovery models have a dedicated module to control the air ride suspension. It is on the CAN bus and is connected to the ABS, ECM and other modules to determine the suspension height, mode and even quick corrections to limit body roll and brake dive. The module uses information like ambient temperature for proper operation of the compressor.
Land Rover has issued revised software for the air suspension control module to cure everything from issues at high altitudes to key-off height corrections. Check for the latest version and TSBs if you run into a problem that might be intermittent.
Ride Height Sensors
Since the late 1990s, Land Rover has used Hall Effect ride height sensors. These sensors not only measure the position of the suspension, but also the rate of movement. They are supplied with a voltage of around 5 volts. The signal voltage is changed as a magnet moves past a coil. Internally, it is difficult to damage one of these sensors. Externally, the linkage that connects the sensor to the suspension arm can be damaged. On some sensors, the linkage is serviceable; on others, it might require a new sensor.
On a scan tool, compare the values of the ride height sensors side to side. The readings will have a specification for height side to side, which is typically between 5-10 mm. You can get strange readings from sensors if there is a bad connection or a wiring problem. But, if there is a short or open, the value will stay at a high or low value that is impossible. This is when a code is set and the system goes into fault mode and the ride height is kept with pressure readings.
The connector can be damaged and cause a short or open. A code will be set when this happens. If a sensor is replaced, it must be calibrated after it is installed.
Any time a ride height sensor or a module on a late-model Land Rover is replaced, you should perform a calibration of the air ride system. This requires a scan tool that is able to communicate with the air ride module. Not calibrating the system can result in codes, and the system can go into a default mode. This can lead to an unhappy customer.
Before a calibration procedure is carried out, make sure the tires are at the correct pressure. And be sure to charge the customer for the calibration procedure.
Air Springs (Bags)
Air springs are no longer the weakest link for Land Rover models. Since 2002 with the introduction of the L322 platform, Land Rover has consistently improved its air bag designs and materials. However, that does not mean that they will not eventually leak.
On older models, the front springs would dry rot before the rear. Oftentimes, this was due to the heat from the engine bay and oil leaks, plus the fact that they are mounted lower on the frame rail and lower control arm. In 2002, the L322 configuration moved the air spring to the top of the strut.
If you are looking for a slow leak, the spray bottle and soapy water method might work. On newer models, it might be difficult to spot the leaks at the top and bottom of the air bag. If you have the factory IDS or SSD tool, it is possible to perform a leak decay test where you can check the ride height over time while the system isolates the corners.
The air line connectors at the springs and reservoir can also leak. It is possible to trim the hose and reconnect the fitting.
Most Land Rovers use a single-piston, high-pressure air supply compressor. The typical compressor can generate more than 200 psi, and there is a pressure relief valve on the compressor that is set at approximately 250 psi. Many of these compressors also have a valve to keep the pressure at a minimum of 40 psi. Most air springs have a burst pressure above 450 psi.
These compressors have a fixed piston that tilts in the cylinder. The cylinder is sealed with a ring made of phenolic resin or similar material. The ring is not lubricated and is designed to wear.
The compressor is used to fill the reservoir on most systems. 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.
Over time, because of wear in the compressor, it will not generate enough pressure to recharge the reservoir.
The system will sense that the compressor is not generating enough pressure to fill the reservoir by measuring the amount of time the compressor has to run under a given set of conditions (ambient temperature and barometric pressure) to change pressure.
If the compressor is not able to fill the reservoir in a given period of time, it will set codes and lock the suspension into a predetermined ride height, while performing the bare minimum corrections to conserve air in the reservoir and minimize compressor run-time.