The apparatus detects error in transceivers of individual modules connected to a communication network, the network being a two-line network. The apparatus comprises a reference voltage source to output a first and second reference voltage value in response to a control signal. A controller controls a predefined sequence of steps in performing a test to detect the errors of the transceivers. A first and second comparator compares a voltage of the corresponding first and second line to a select first and second reference voltage as commanded by the sequence of steps of the test sequence. A first and second latch device is triggered by an output signal of a corresponding first and second comparator as a result of the compare operation, the first and second latch device being placed in a state which indicates the relative voltage level of the signal to the reference voltage and is subsequently detected by the processor to determine whether the voltage level of the first line and second line is stuck at a fixed predetermined level thereby indicating an error of the transceiver under test.