MAY 2023 AFTERMARKET 29 www.aftermarketonline.net on cylinder 2. Please refer to Fig.2. However, the actuator blocked fault had not returned. This told me that the software had indeed been altered but with the car still under-boosting, the vehicle still had an issue that I needed to find. I could now proceed knowing the software was standard, and remove that from the list of possible causes. Re-checking everything, the only fault I could find was the amount of travel the turbo actuator made, from 5% to 90%. I actuated it with a scan tool, but I could not prove whether it was correct or not. Luckily, speaking to a good friend about the problem, they said they had a Mercedes in with the same engine for service. My friend was able to film a good test of the actuator and send me the video to compare. It was at this point I knew this was my problem as the video showed the actuator not only moving further but also much faster. Testing the wiring to the actuator proved it to be good, and checking fitting instructions showed no adaption resets. Checking on multiple scan tools showed no resets, so I was happy to call out the actuator as being faulty. The customer was contacted with prices and was happy to proceed with a new actuator and injector. Once both components were replaced, I carried out the same test with the scan tool forcing the actuator from 5% to 90%, but to my horror the travel was identical. At this point, I was a little lost as I felt I had covered all bases but was no further forward with fixing the fault. It felt like the unit needed to be learned by the control unit. However, using Autologic, which is Mercedes-based, it did not list a re-set, and double-checking fitting instructions showed no mention of re-setting anything. Afterwards though, I decided to try some aftermarket scan tools for an option and the first two showed nothing. Plugging in Autel and going deep into the menus showed a boost pressure positioner teach in process. Before running the procedure, I decided to plug back in the old turbo actuator, as I am not one to fit parts which are not needed, and if the old unit could be relearned, the new part would not be required. Sadly, the procedure kept failing, so I plugged the new unit in and re-tried and the procedure completed successfully. Attempting the same actuation test as before now showed the actuator arm to match the known good video in terms of speed and travel. Adjustment range The old unit for some reason had gone faulty, but had defaulted to a state of not being adapted to the control unit and randomly logged a stuck closed fault. Even though, for the most part it didn’t operate, it worked enough to allow the turbo to create boost, albeit slower than normal. As can be seen in Fig.3, the procedure on Autel lists that when successful, the adjustment range should change within 150ms however when not taught, it would be one second which matched my fault. I just wish I had found this option earlier but was happy to have finally found and rectified the issue. As you can see in Fig.4 and Fig.5, the difference in arm travel is visibly noticeable. Confident the fault was fixed, I then road-tested the car again and the vehicle now drove like a different car, with strong acceleration and boost more like what you would expect from an AMG Mercedes. Upon returning to the workshop and checking for fault codes, I now had no fault codes stored so was happy the vehicle was finally repaired. The customer reported after a few days the car was like a new Mercedes as it drove so well. Once again, like my other articles, this job shows the importance of a solid test plan and system knowledge to find the cause of seemingly insurmountable problems. Above: Fig 3 Below: Fig 4
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