Fan speed sensor circuit (T123) no signal
- Start the engine and check that the fan turns. Check if the fan speed signal is plausible - Check the wire harness to the fan. - Check the belt transmission. (Only if fan is geared up). - If no fault found on belt transmission or wire harness, replace the fan.
What you'll see
No driver-visible symptom recorded.
System reaction
If there is an electrical failure on the sensor or wire harness, the control unit will demand fully engaged fan and the fuel consumption will increase. If there is a mechanical failure, There will be no fan cooling and the cooling capacity will be dramatically reduced. Can lead to torque reduction
Diagnostic depth
No signal from the fan speed sensor. The test does not run unless the engine coolant temperature is at normal operating temperature. This assures that the oil in the viscous coupling is not too cold.
- Electric short or open ciruit in the fan harness. - The speed sensor in the fan coupling is broken. - Belt in belt transmission is broken. (Only if fan is geared ). - The fan coupling is damaged.