Aftermarket June 2022

I was recently asked to look at a Mercedes Benz C- Class 250D. This vehicle came from an auction. My customer, a car dealer, asked me to see if I could help him, as all the repairs they had performed to date had failed, with the engine management light still illuminating intermittently. What seemed like a routine task turned into a much deeper diagnosis than should have been required. Before I start my diagnosis process, I always approach the customer to ask if they have any history of the vehicle. Other than their repair attempts, which included a differential pressure sensor and pipework being installed, he knew of no other work that had been performed. This can be problematic because I did not have any information regarding when the fault started to appear. I sought this information because it can often help me repair the vehicle a lot more quickly. I started with a full system scan. If you refer to Fig.1, you will see the scan revealed two fault codes being stored. As you can see, the two codes present were for the exhaust temperature sensor bank 1, sensor 1 and exhaust pressure too high, bank 1. With any fault related to the diesel particulate filter (DPF), it is critical to address the root cause of the blockage, rather than only fixing the blockage first. Otherwise, the DPF will just block up again. Therefore, it was essential for me to address the exhaust temperature bank 1 sensor 1 fault. By removing the airbox I was able to gain direct access to the sensor and the connector. A few quick tests verified the sensor had good voltage and ground supply. This left me to verify and condemn the sensor as being an open circuit. A new sensor was installed, and the vehicle was then rebuilt. I interrogated the engine ECU and cleared the exhaust temperature sensor fault code. After verifying the sensor was now operational, in live data, I then turned my attention to the DPF being blocked, as indicated by the 26 AFTERMARKET JUNE 2022 TECHNICAL www.aftermarketonline.net SOFTWARE MANIPULATION AND HOW TO CATCH IT! A Mercedes-Benz that Ryan recently encountered provided him with an opportunity to muse on software manipulation scan tool PID. Viewing the live data from the differential pressure sensor, which was replaced by the car dealership, I found the backpressure at idle to be 40mbar, and more than 150mbar at 2,500RPM. This indicated a partially blocked DPF. This was then verified using a manometer. This device is used to measure smaller pressures. I suspected this blockage was due to the initial fault of the exhaust gas temperature failing. Therefore, I carried out a clean using JLM's two-stage cleaning solution. This procedure brought the pressure down to 5mbar at idle. After carrying out the clean I reset the DPF adaptation data and monitored the soot accumulation figures on a road test. This confirmed both the adaptation was successful, BY Ryan Colley, Elite Automotive Diagnostics Fig.2 Fig.1