Yesterday i implemented a test setup with a PCM1690 audio DAC, using KL10 I2C1 for control. When i looked at SDA with the scope, i found the ACK from the slave was at about 0.4 V. Though within specs, this looked ugly. I checked the pullup current and found the pullup resistor was about 150 Ohm. The error was in the I2C1 pin configuration. When i used the PORTx_PCRn configuration bit ODE (open drain enable) in addition to the pin MUX setting, everything looked perfect.
I am writing this note, because it's an error that may go unnoticed. I don't have time to check the Kinetis sample code, today i have to do the I2S part.