Started our GL350 up this afternoon & the transmission went into "limp mode". We have a T-Mobil wifi device that plugs directly into the vehicle's OBD II port. It sent the following text to my wife's phone: "Diagnostic Trouble Code (DTC) Detected, Code: P2454. Powertrain, Auxiliary Emission Controls, Fault: 54". Any ideas anyone? Turned the vehicle off and back on it is now out of "limp mode".