I have a 2013 Hyundai Elantra with automatic transmission. Recently the car loses power when trying to accelerate and stalled a few times (flooring it does nothing). The tachometer gets stuck @ 0 while driving regardless of speed and acceleration. I also just noticed today that nothing happens when I try to downshift manually.

But it doesn’t always happen. Sometimes it works just fine and the tachometer pops back to life. When I brought it to my mechanic he couldn’t observe the problem and no error codes came up (and didn't seem to think that it was a transmission problem).

Any insight as to what the problem might be or what I should tell the mechanic to check would be greatly appreciated.

 

The tach signal is trying to tell us something.

More examining of crank sensor and signals coming from it are in order. It could be a sensor problem, a wiring problem between the sensor and the PCM
Usually when the crank signal is interrupted or lost intermittently the engine will almost stop running. Crank sensor circuits don't usually produce a code.

 

Thanks. The tach works when the engine works normally and then it goes dead when the engine acts up.