BMW F11 5 Series Touring: one side high, and the air lines swapped.

What came in

A 2011 BMW 530i Touring, the F11 5 Series estate, with self-levelling air suspension at the rear. The left rear corner stayed high and felt hard. There was a big difference in ride height between the left and right.

A lot had already been done to it. Two new level sensors had been fitted. The air suspension valve block had been replaced. The control unit had been flashed back to standard software, so the system should have been behaving as it left the factory.

The calibration would not take

The normal next step after new sensors is a ride-height calibration in ISTA, BMW's workshop software. You measure each wheel's height and enter the figures, and the car learns them.

It failed. ISTA reported that it could not write the values to the control unit while we were entering the height for each wheel.

A failed calibration is not much use as a diagnosis on its own. It told us the system was not in a state to be calibrated, not why.

Testing the air side

So we stopped working through the software and tested the air itself. The question was simple: when the system tries to let air out of the left rear bag, does the air actually leave?

With the car on the two-post ramp, we supported the left lower arm on a screw jack and opened the left air line at the valve block. It hissed, and the bag went completely soft.

That told us a lot. Pressure had been trapped in the left bag. The bag and its line could hold air. The air just had no way out through the valve block when the system asked for it.

What we found

The rear air lines were connected the wrong way round at the valve block: the left bag's line on the right port and the right bag's line on the left.

Our reading is that when the system tried to let the left corner down, it was working on the wrong bag. That fits a corner stuck high and hard, and a calibration that would not complete. We swapped the lines back to the correct ports. With that done, the next step is to let both bags refill, check each corner raises and lowers on command, and then run the calibration again.

What to watch for

• New parts do not prove the fault has moved. This car had new sensors and a new valve block, and the symptom was still there. When it survives new parts, look at how the parts were fitted.
• One corner high and hard means trapped air. A bag that will not come down is usually not a leak. Find out whether the air can get out.
• Check the port layout after a valve block change. The lines are easy to cross and the result looks like a failed component.
• Do not calibrate around a fault. If the ride-height calibration will not accept values, fix the air side first and calibrate afterwards.

If your BMW is sitting unevenly, start with our BMW specialist page or the diagnostics page.