Method for diagnosing an earth fault of a start/stop unit of a motor vehicle

A method of diagnosing a ground fault of a start/stop unit (4) adapted to control the starting and the stopping of a vehicle motor, said unit being part of a start/stop device (10) further including a ground output (3), said device (10) being further associated with a driver device (11) including a circuit (15) for reading the status of the start/stop unit, said diagnostic method comprising:

• in a preliminary phase:
• equipping the driver device (11) with a ground (20) switchable between two positions and connecting the ground output (3) of the start/stop device (10) to said switchable ground (20),
• during operation of the vehicle, at the time of a start/stop instruction:
• reading (step 210) a first value of the signal present at the input of the reading circuit (15), then,
• temporarily switching (step 220) the switchable ground (20) from a first position connected to a ground (16) of the vehicle to a second position connected to a ground resistor (RM),
• reading (step 230) a second value of the signal received by the reading circuit (15) during the switching of the ground to the resistor (RM), and
• comparing the first and second values (step 240), and
• if the first and second values read are significantly different, diagnosing an absence of a short-circuit to ground,
• if the first and second values read are substantially equal, diagnosing (step 260) a short-circuit to ground fault of the start/stop unit (4).