A method for operating an electro-pneumatic parking brake module (10, 10', 10") for an electronically controllable pneumatic brake system for a vehicle, in particular a commercial vehicle, the module having a supply port for receiving a supply pressure (pV), at least one parking brake port for connecting at least one parking brake cylinder, a main valve unit which receives the supply pressure (pV) and which is configured to control a spring mechanism pressure (pF) at the parking brake port as a function of a control pressure (pS), a pilot valve assembly, which receives the supply pressure (pV), for providing the pilot pressure (pS), the pilot valve assembly having a bistable valve which is switchable between a first ventilation position and a second venting position, and a control unit for providing first and second switching signals (S1, S2) to the pilot valve assembly, the pilot valve assembly having a monostable holding valve which is pneumatically connected in series with the bistable valve and is arranged in a control line of the main valve unit, the holding valve being opened in an open position in a currentless state, and the control unit being configured to hold the holding valve for holding the control pressure (pS) in the holding position by means of the first switching signal, and an auxiliary adjusting port being arranged in the control line for receiving an auxiliary control pressure (pZ) which is provided at an auxiliary brake pressure port, the method having the step of: - filling the parking brake cylinder by pressurizing the control port (52.4) of the main valve assembly to control the spring mechanism pressure (pF) at the parking brake port as a function of the control pressure (pS), - the control port (52.4) being pressurized by means of an auxiliary control pressure (pZ) which is provided at the auxiliary brake pressure port and is accepted via the auxiliary adjusting port, - the holding valve automatically switching to an open position to vent the control port (52.4) in the event of a fault in an electronic component, in particular in a control unit of the brake system, and/or in the event of a power failure, the control port (52.4) of the main valve assembly being vented in order to vent the parking brake port, characterized in that - for holding the auxiliary control pressure (pZ) at the control port (52.4), the holding valve is held in the holding position. a supply port for receiving a supply pressure (pV), at least one parking brake port for connecting at least one parking brake cylinder, a main valve unit which receives the supply pressure (pV) and which is configured to control a spring mechanism pressure (pF) at the parking brake port as a function of a control pressure (pS), a pilot valve assembly, which receives the supply pressure (pV), for providing the pilot pressure (pS), the pilot valve assembly having a bistable valve which is switchable between a first ventilation position and a second venting position, and a control unit for providing first and second switching signals (S1, S2) to the pilot valve assembly, the pilot valve assembly having a monostable holding valve which is pneumatically connected in series with the bistable valve and is arranged in a control line of the main valve unit, the holding valve being opened in an open position in a currentless state, and the control unit being configured to hold the holding valve for holding the control pressure (pS) in the holding position by means of the first switching signal, and an auxiliary adjusting port being arranged in the control line for receiving an auxiliary control pressure (pZ) which is provided at an auxiliary brake pressure port, the method having the step of: - filling the parking brake cylinder by pressurizing the control port (52.4) of the main valve assembly to control the spring mechanism pressure (pF) at the parking brake port as a function of the control pressure (pS), - the control port (52.4) being pressurized by means of an auxiliary control pressure (pZ) which is provided at the auxiliary brake pressure port and is accepted via the auxiliary adjusting port, - the holding valve automatically switching to an open position to vent the control port (52.4) in the event of a fault in an electronic component, in particular in a control unit of the brake system, and/or in the event of a power failure, the control port (52.4) of the main valve assembly being vented in order to vent the parking brake port, - filling the parking brake cylinder by pressurizing the control port (52.4) of the main valve assembly to control the spring mechanism pressure (pF) at the parking brake port as a function of the control pressure (pS), - the control port (52.4) being pressurized by means of an auxiliary control pressure (pZ) which is provided at the auxiliary brake pressure port and is accepted via the auxiliary adjusting port, - the holding valve automatically switching to an open position to vent the control port (52.4) in the event of a fault in an electronic component, in particular in a control unit of the brake system, and/or in the event of a power failure, the control port (52.4) of the main valve assembly being vented in order to vent the parking brake port, characterized in that - for holding the auxiliary control pressure (pZ) at the control port (52.4), the holding valve is held in the holding position. - for holding the auxiliary control pressure (pZ) at the control port (52.4), the holding valve is held in the holding position.