I'm pretty sure it's the ambient air sensor. The LR3 has a sensor you can buy separately, JTF000052. But somehow the LR4 decided that you can only get the sensor as part of the lower air guide, LR055300.
FYI... I bought the LR055300 lower air guide and found out my was working fine and tried to return it. The restocking fee was 15% and to ship it back was $50+, so it's just sitting my garage.