Temperature sensor for a motor vehicle comprising: - a thermocouple comprising two metal wires welded together at a first end forming a hot weld for measuring a temperature T1 in the motor vehicle, said two metal wires each comprising a second end intended to be electrically connected to an electronic device or an electrical harness, and - a first thermocouple portion in which an insulating sheath surrounds the metal wires of the thermocouple, the two metal wires of the first thermocouple portion being separated by a distance D, - a second thermocouple portion not covered by the insulating sheath extending from the first end of the metal wires of the thermocouple to a front end of the insulating sheath over a length of between 6 mm and 10 mm, the said second thermocouple portion comprising a narrowed end part in which the two metal wires of the second thermocouple portion are separated by a distance d which is less than the distance D separating the metal wires of the first thermocouple portion, the distance d between the two metal wires of the second thermocouple portion is between 1 mm and 2 mm, and - a cap surrounding the second thermocouple portion to protect the hot junction, comprising: - a first tubular portion surrounding the narrowed end part of the second thermocouple portion and comprising a first closed end facing the first end of the metal wires of the thermocouple, - a second portion comprising a first part surrounding the insulating sheath connected perpendicularly to a second part abutting the front end of the insulating sheath, and - a third portion in the form of a truncated cone connecting the first tubular portion to the second part of the second portion, the second part having the shape of a disc with an orifice at its centre. - a thermocouple comprising two metal wires welded together at a first end forming a hot weld for measuring a temperature T1 in the motor vehicle, said two metal wires each comprising a second end intended to be electrically connected to an electronic device or an electrical harness, and - a first thermocouple portion in which an insulating sheath surrounds the metal wires of the thermocouple, the two metal wires of the first thermocouple portion being separated by a distance D, - a second thermocouple portion not covered by the insulating sheath extending from the first end of the metal wires of the thermocouple to a front end of the insulating sheath over a length of between 6 mm and 10 mm, the said second thermocouple portion comprising a narrowed end part in which the two metal wires of the second thermocouple portion are separated by a distance d which is less than the distance D separating the metal wires of the first thermocouple portion, the distance d between the two metal wires of the second thermocouple portion is between 1 mm and 2 mm, and - a cap surrounding the second thermocouple portion to protect the hot junction, comprising: - a first tubular portion surrounding the narrowed end part of the second thermocouple portion and comprising a first closed end facing the first end of the metal wires of the thermocouple, - a second portion comprising a first part surrounding the insulating sheath connected perpendicularly to a second part abutting the front end of the insulating sheath, and - a third portion in the form of a truncated cone connecting the first tubular portion to the second part of the second portion,