If you are experiencing limp mode after replacing the oil cooler seals on your OM642 engine in the Jeep Grand Cherokee CRD, Sprinter Vans or Mercedes BlueTEC models the good news is that it is probably an easy fix.
The ECU will show codes for the MAFs and IAT sensors, potentially more. The first thing to know is that codes that cannot be cleared or reappear immediately even with the engine off are and indication that the sensors are no longer connected. First, check that all connectors are properly seated – the Mercedes connectors need to be fully seated, and “CLICK” into place, or else they will not get a good signal.
If you are certain the connectors are fully seated then you probably blew the fuse that these sensors all get power from, especially if you did not disconnect the battery before starting the job.
The fuse that powers all these sensors is located in the fusebox under the hood. It is a 15 AMP fuse located here:
If you pull that fuse you will see that it has blown – e.g. the wire inside the fuse has broken.
Get a replacement 15A fuse. DO NOT PUT A HIGHER AMP FUSE IN THAT LOCATION. Fuse amperage is carefully chosen by the engineers designing the electrical system. Fuses blow to protect other electrical components. Putting in a higher amp fuse can expose more expensive components & wires to currents they cannot handle.