2006 Dodge Sprinter 2500 (Mercedes 2.7L Diesel, Nag-1 Transmission) P0730 Code: Limp Mode, TCM Replacement & Rebuild Issues

Vehicle: 2006 Dodge Sprinter 2500 (Mercedes 2.7L diesel, Nag-1 transmission), 100,000 km, built in Germany. At approximately 99,800 km, the vehicle entered limp mode — only speeds 1, 2, and reverse were available. A Mercedes dealership diagnosed a faulty Transmission Control Module (TCM). I replaced the TCM with a used unit matching the 2006 model year. After testing in urban areas under 60 km/h, the vehicle operated normally. However, on highways, the transmission was limited to third gear — no fourth or fifth gear, and no torque converter lock-up clutch engagement occurred. I returned to the Mercedes dealer to install a new TCM, but they flashed the used unit and claimed it was functioning properly. Unfortunately, the used TCM triggered P0730 code, leading them to conclude that either transmission replacement or full rebuild is required — both being costly. A recommended transmission specialist rebuilt the transmission and torque converter. After clearing the P0730 code, the issue returned repeatedly, resulting in a 'Controlled Limp-in Mode' where only gears 1, 2, and 3 were available. The first time I shifted into Drive (D), the TCM immediately registered P0730 as 'Pending,' even when the wheels had not rotated. The specialist could not resolve this issue and advised towing the vehicle back to a Mercedes dealership. The transmission has now been fully rebuilt with new components — there are multiple orifices in the shift body valve, which may be contributing to the problem. According to the Mercedes Service Manual (Section 3.2.6: Transmission Adaptations), 'This TCM function should be used when a new transmission is installed to reset the TCM adaptive settings to factory defaults.' Could this procedure resolve the recurring P0730 issue? Any insights or solutions from experienced users would be greatly appreciated.