The part is a black plastic box about the size of the palm of your hand. It has part numbers and serial numbers clearly visible on it. In the Fusion Energi the location of the modem in the car was under the flat area under the rear window behind the back seats. Quite difficult to figure out how to remove that top panel to see the part. The location is likely different in your CMax though. I had something similar happen in my Fusion 2014 energi. Modem stopped working in January 2018 in Vancouver. Because I find it hard to believe that an electronic part like this would just fail after 3.5 years, I started researching online and found messages like this. In some cases the modem replacement service on bulletin 15N04 was not actually performed. I'd taken mine in last year, I think, to have that service done where they'd replace the modem with a 3G version. Service was apparently completed. According to the 15N04 service bulletin here: https://ford.oemdtc.com/2653/15n04-embedded-modem-replacement-2012-2016-ford-2015-lincoln Your TCU modem should have part number GM5Z-14G229-BD. If it does not, your modem was not replaced correctly. I was able to verify that the modem in my car, after this service bulletin was completed, is in fact NOT the correct part.