Last month a customer brought in a 2013 Audi S7 with three problems: The automatic suspension system and automatic radar control headlights were not working properly, and he was also having an intermittent problem with his start-stop switch.

When the car arrived, we could see that the rear automatic shocks were not working correctly and the back of the car was sitting low to the ground. When we drove the car into the shop, the instrument cluster looked like a Christmas tree. There were warning lights on for automatic suspension and adaptive headlight controls.

Because the rear suspension was deflated, there was no reason to test-drive the car until we communicated with all of the control modules via the scanner. Once we had the car connected to the factory tool (Odis), we pulled several codes across multiple control units.

From the automatic height control module, we pulled codes 34 (level control), 677384 (ride height system plausibility error), 677385 C1046 (ride height system plausibility error), 403200 C10C8 (function shut off active) and fault P178E 00 115968 (function limitation due to excessive temperature). From the headlight range module, we pulled code 120589 (function restriction due to faults starred in other modules). There were no codes in the start-stop module. There were also a few power control codes in other modules, but they were not active.

We focused on the automatic height control system first.

The purpose of the automatic suspension system is to control the car’s ride height and the damping of the suspension automatically. The car has position sensors on the suspension that measure the height of the car. The position sensors then send information back to the suspension computer. The suspension computer also gathers information on the car’s speed, yaw rate and braking. The suspension computer then takes all that information to adjust the ride height to the car’s environmental condition.

Generally, there are two control types of automatic suspension systems. One uses hydraulic pressure and the other uses air pressure. The Audi that we were working on uses air pressure.

Diagnosing the problem

The first thing we did was clear all codes in the height control system and try to reset the ride height. As soon as we cleared the codes, they returned right away. With the scanner connected, we then tried to activate the air suspension. We could not control the suspension from the scanner and saw that the air compressor was overheating; it was at 111 C (nearly 232 F). We then gained access to the air suspension compressor and found the compressor wire and connector were melted. It got so hot that it melted the car’s body harness as well.

We had found out why the air suspension was not working, but we did not know what had caused it to overheat. We then inspected the air suspension power control relay and found no damage to the relay. In the process of ordering the air compressor, I found that we were to replace the air compressor relay at the same time. It is possible that the new relays have been updated. Sometimes relays can stick open and let current flow to a component unmetered. If that happens, the uncontrolled current flow can burn up motors and wiring harnesses.

Once we installed the new air compressor and new relay – and repaired the wire harness – everything worked great. We were able to run and adjust the ride height. As soon as we repaired the suspension, the headlight aiming system also came back online.

We then checked the headlight adaptation and test-drove the car. The headlight system actually never had a problem, but it was being affected by the car’s ride height. These systems work in tandem so that the headlights will stay in the optimum position as the car moves down the road.

We were never able to reproduce any problems with the start-stop switch, and there were no codes in the start-stop control module. If we find something in the future repairs, I will make sure to write about it.

It is really amazing to think how many control modules are dependent on one another. As we become more accustomed to all of this technology, it makes me wonder how we used to drive cars without computer controls.

Matt Pataky owns Sunnyvale Foreign Car Service, 15 Pioneer Way, Mountain View. For more information, call 960-6988, email sfcsmv@gmail.com or visit sunnyvaleforeigncar.com.