Airing Out the Problems

April 18, 2014 | Reply More

In the first year of the new millennium, BMW introduced a new air suspension on its X-Series vehicles. This compensates for load by controlling the ride height of either the rear axle, or all four wheels in later versions. But what do we do when they stop working?

We generally don’t take any notice of things we use every day as long as they’re working fine. We just take them for granted. The moment something goes wrong, however, we are often at a loss as to what happened. This is especially true of our cars. We rely on them, we depend on them. When something goes wrong we need to get it diagnosed and repaired as fast as possible.

There is no doubt vehicles are getting more complicated. Some of the add-ons may appear frivolous, but some of the technology significantly adds to the safety of a vehicle. This is particularly true of the suspension system. BMWs are typically known for their sporty, precision handling – it’s a big part of their reputation. It improves safety by providing the driver with excellent cornering control. After all, the most important safety feature of any car is its ability to avoid a collision in the first place.

What’s the Purpose?

The air compressor assembly is mounted underneath the spare tire. This is the EHC I system, so what you are seeing here is the compressor, compressor relay, and the two air spring solenoids. You can electrically test everything from here. EHC II is a little more involved.

The air compressor assembly is mounted underneath the spare tire. This is the EHC I system, so what you are seeing here is the compressor, compressor relay, and the two air spring solenoids. You can electrically test everything from here. EHC II is a little more involved.

The BMW X5 represents a new breed compared to the standard-issue SUV. It was dubbed both an AAV (All Activity Vehicle) and SAV (Sport Activity Vehicle), and it provides a level of handling that’s superior to that of most of its competitors. One of the factors in that is its finely tuned sporting suspension system with electrical compensation (very similar to that of the E39 wagon). The X5 uses a multi-link rear suspension system that carefully controls the caster, camber, and toe of the rear tires to provide optimal handling as the vehicle is subjected to a variety of situations ranging from hard cornering to light off-road excursions.

It also has a larger load carrying capacity than its sedan counterpart. This means the additional load may change the ride height, throwing off the carefully-designed suspension geometry of the rear axle. Not only will this change the handling characteristics of the vehicle, but if driven long enough will cause uneven tire wear patterns requiring more frequent rotations and replacement. So, a system that can maintain the same ride height regardless of the weight in the vehicle will preserve handling and tire life.

Starting in 2000, the X5 got EHC (Electronic Height Control). This system uses pneumatics to maintain the ride height of the rear axle to compensate for weight carried in the luggage compartment (this is why a nearly identical system is found in the E39 wagon). As stated earlier, this keeps the suspension at the

 

Login to continue reading this article.

Not a member? Register for FREE access.


Lost your password?

Tags: ,

Category: Steering + Suspension, the bimmer pub

Leave a Reply

You must be logged in to post a comment.