Heavy Metal! - July - 2022

An Audi Opportunity! An OB5 Transmission With Issues Inside AND Outside

When a vehicle comes into your shop with multiple codes, it is usually tricky to figure out where to begin. Sometimes electrical and mechanical faults are so substantial and evident that choosing what should be addressed first is challenging. The choice is compounded when working with European-made vehicles. I like to refer to such tough cases as opportunities.

As we all know, BMWs, Mercedes, Audis, and Volkswagens each have quirks of their own; especially on the electrical side. Unfortunately, the manufacturers leave the aftermarket at a disadvantage with little diagnostic reference material. As a result, shops choose to steer clear of these vehicles even when it’s obvious the transmission needs to be rebuilt. However, in the case of a 2015 Audi S4 Prestige Premium Plus equipped with the OB5 (DL-501) DCT transmission, the opportunity was met head-on!

The vehicle came into Gold Coast Transmissions in Florida, where my close friend, Steve, was responsible for diagnosing the problems. The car came in with numerous codes (figure 1) and a unit that needed internal repairs. Given the extent of internal damage to the transmission and the projected parts to be replaced, the decision was made to handle the obvious first, with a high probability that the codes would also go away.

The OB5 is a 7-speed, DCT transmission with a dual wet clutch. While the OB5 is found in Audi vehicles, variants of this transmission are found in Volkswagen and Porsche. The unit has a valve body that houses solenoids, actuators, sensors, and a TCM. None of these components are sold separately, however the dealer sells a complete assembly called a Mechatronic. The dual wet clutch is also sold as an assembly. However, several aftermarket resources are available to service various internal components. Check with your soft parts supplier for availability.

The unit was rebuilt with a new wet clutch assembly and a 1,500-dollar OEM Mechatronic assembly with all sensors, solenoids, and internal harnesses. After installation and a test drive, transmission codes returned. At this point, it was evident that the problem wasn’t inside the transmission. Instead, we needed to look outside the box.


Just mentioning Audi and electrical problems in the same sentence is enough to make the best diagnosticians break out in a cold sweat! Following a process that starts with the basics is necessary here. So, the battery and charging system conditions were the initial checks made. No issues were found here. The static and cranking battery tests passed with flying colors.

The charging system checked within factory specifications too. Next, the harness and connectors associated with the transmission were inspected.

Lo and behold, issues were found here! A green liquid had found its way to the harness leading to one of the transmission connectors. It was evident outside the harness and didn’t immediately appear to be an issue until the trail of fluid led to the connector. Here, the fluid traveled down the harness, where it could pool on the back of the connector. The connector was separated and revealed that the fluid wicked through the insulation, causing corrosion to the pins and contacts (figures 2 and 3a-3b).

One should never assume that a green fluid is engine coolant with late-model vehicles! So, the coolant reservoir was checked, verified to be green in color, and found to be low (figure 4). The coolant reservoir on this vehicle is located above the transmission with hoses running near the connector and harness in question. A closer inspection showed that a coolant hose rubbed against a wastegate control component, creating a pinhole. Coolant was spraying on the wiring harness as a result. The technician cleaned the contaminated connector, repaired the coolant leak, and corrected the coolant level. With everything together, the vehicle tested with no codes. What a relief!


When you look at individual trees before assessing the forest, complex problems can become a nightmare. In this case, since the vehicle set multiple codes after major components inside the transmission were already addressed, the problem most likely was outside the transmission. Power and ground must be verified from the source to the module whenever multiple codes are set in a module. In this case, the module is a part of the Mechatronic assembly inside the transmission. Therefore, structured steps led to an unexpected area of concern and the source of the issues.

Multiple problems in a vehicle with obvious transmission problems can be scary to tackle.

However, approaching them with a broad scope in view will give you a better chance to turn a problem into an opportunity!

Until next time, see ya!

Thanks to Steve at Gold Coast Transmission for the information!