nRF9151 has three COEX I/O pins. For details on each pin's function, see LTE modem coexistence interface in nRF9151 Product Specification.
The COEX0 function can be configured with the %XCOEX0 AT command. If COEX0 is configured for Global Navigation Satellite System (GNSS) Low-Noise Amplifier (LNA) control, its functionality can be verified in GNSS RX testing.
COEX2 can be monitored during RF TX testing and checked that the pin line is changing states. For more information on configuration options, see COEX0 pin control configuration %XCOEX0 in nRF91x1 Production Test AT Commands Reference Guide.
The COEX interface can be tested also with the %XGPIOTEST AT command that is supported by the Production Test Image (PTI) modem firmware. Each pin can be set to the output mode and to the logic low state (0 V) or to the logic high state (VDD_GPIO). The pin voltage can then be measured with external test equipment. Alternatively, the pins can be set to the input state and the pin status can be read. The result of the test can be compared to an externally set level.
For more information on the %XGPIOTEST AT command, see Modem GPIO functionality test %XGPIOTEST in nRF91x1 Production Test AT Commands Reference Guide.