Series resistor. Porsche 986 Boxster / 996

Series resistor for front cooler fan.
The Genuine Porsche 99661610100 is the factory-spec series resistor used to control the speed of the auxiliary radiator (cooling) fan on select Porsche 986 Boxster and 996 Carrera / 996-series models.

Fits:
Porsche 986 Boxster 1997 - 2004
Porsche 996 C2 / C4 / C4S 1998 - 2005
Porsche 996 GT3 / GT3 RS 1999 - 2005
 
Diagram Ref No 4.

This resistor modulates the electrical current to the cooling fan, allowing the fan to run at different speeds (low and high) depending on engine and coolant temperature demands. By enabling variable fan speed instead of only full-speed operation, it helps regulate engine temperature more precisely, reduces noise when full cooling isn’t required, and ensures efficient radiator airflow under load or idle conditions.

Replace the resistor when:
• The cooling fan only works at high speed or fails to run at low speed (indicating resistor failure).
• Fan runs intermittently or erratically, or coolant temperatures climb under idle/traffic conditions.
• Heat-related failures (resistor overheated, wiring insulation damaged) or exposure to moisture/age has degraded the resistor.
• Cooling system overhaul: radiator or fan motor replacement, or when restoring an older 986/996 to maintain OEM reliability.

Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.

99661610100

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