EV Mode switch

Could be any number of reasons. According to the Owners manual:

It may not be possible to turn EV drive mode on in the following situations. If it cannot be turned on, a buzzer will sound and a message will be shown on the multi-information display.
●The temperature of the hybrid system is high.
The vehicle has been left in the sun, driven on a hill, driven at high speeds, etc.
●The temperature of the hybrid system is low.
The vehicle has been left in temperatures lower than about 68F (20C) for a long period of time etc.
●The gasoline engine is warming up.
●The hybrid battery (traction battery) is low.
When the amount of remaining hybrid battery (traction battery) charge displayed on the meter or Display Audio system is low. (P. 35)
●Vehicle speed is high.
●The accelerator pedal is depressed firmly or the vehicle is on a hill etc. ●The windshield defogger is in use.

If it actually is in EV Mode and the dash simply isn't indicating it, then that's a different issue.

 

I just hit 100,000 miles on my 2012 C. 4 years ago when I first got the car I tried the EV switch, and realized it was pretty much useless. Most likely yours was acting normal. If not and its actually broken, you will never miss it. It puts the car in electric only mode, which is good for very low speeds and at best about 1 1/4 miles before the battery runs dry.

 

Rj's right, EV mode is quite pointless however it should display that black letter on green EV symbol on your information screen and if it doesn't I would just take it to the dealer and have them check it out as it may or may not be a symptom of a greater underlying problem.

 

I agree that EV mode is pretty useless in general, however I often use it when I first start to car to prevent the engine from firing up until I back out of the garage and am actually underway.