Mercedes CLK Diesel Transmission Problems

I understand your concern. I had a similar experience with my CLK, including erratic shifting and limp mode. While it could be a faulty transmission control unit, a comprehensive transmission diagnosis is important to ascertain whether the issue stems solely from the ECU or if there are underlying mechanical issues within the transmission itself. Before committing to a transmission repair, I suggest a thorough inspection of the transmission fluid and valve body. Has the fluid level been checked? What is the condition of the fluid? Burnt or discolored fluid, or the presence of metallic particles, would indicate more extensive internal wear. It would be judicious to undertake further investigation before assuming ECU failure to be the sole cause. I strongly suggest you check those before spending money on an ECU replacement.

Fluid level is good and the fluid was changed about 20000 km ago. I checked for metal shavings when it was drained, but found nothing unusual. A transmission diagnosis was performed with Mercedes diagnostics and it shows a code related to the TCU specifically. What else could it be besides a fried car computer?

Given that the fluid appears to be in acceptable condition and a diagnostic code points directly to the TCU, it is indeed becoming increasingly probable that the control unit is the primary source of the transmission problems. However, it would still be prudent to consult with a qualified workshop specializing in Mercedes vehicles before proceeding with the ECU replacement. They can perform further diagnostic tests to definitively confirm the TCU's failure and also check the wiring harness and connections to the TCU. While I understand your inclination towards a DIY approach, these systems are complex, and the potential for unintended consequences is significant. A workshop will possess the specialized tools and expertise to ensure a proper transmission repair and avoid exacerbating the issue.

I appreciate the feedback. I was hoping to avoid the shop, but you're right. It's likely beyond my capabilities without specialized tools. I'll get it towed to a reputable Mercedes shop for a proper diagnosis and transmission repair. Thanks again.