The CTS (Coolant Temperature Sensor) measures the temperature of the coolant in the radiator and based on that, sends info (in the form of 'resistance') to control the auxiliary fans operation.

Some cars have only one (1) aux fan. Some, like my S500, have two (2). Merecdes has set that the low speed fan operation starts when the coolant temperature reaches 100C. But practically speaking, the fans usually come on between 102 -105C.

My Cool Harness changes the effective reading telling the controller that the temp is higher than it really is, thus starting the fans at a lower temperature. For example, the CH-92 model turns the fans on around 92C. Overall, this effect keeps the operating engine temperature about 8 degs C cooler.

This is not the four terminal ECT (Engine Coolant Temperature) sensor which controls the engines's fuel mixture, etc.. In the picture above, it's next to the blue circled CTS (round black connector).

For more info, check my page (www house below) and click on the MENU #17.

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Regards . . . . JimF
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'94 S500 Cpe

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