The temperature gauge of the car will reads hot when stuck on traffic. The possible cause of the problem is a faulty fan motor, sensor or switch. Other reason is a slipping fan belt. Temperature Gauge that Reads Hot Possible Causes Faulty Fan Motor, Sensor or Switch If the car is equipped with an electric fan then the possible cause is that the motor, sensor, or the switch is faulty. The purpose of the fan is cool down the engine when the car is stopped or moving at low speed such as during traffic. Since your car is equipped with an electric fan those three parts mentioned above is possible cause of the problem. When the fan motor is faulty the fan will not function to cool the engine. The purpose of the coolant sensor is to measure the temperature of the coolant, when the temperature is high the fan will be triggered to cool down the engine, now if the sensor is faulty the fan will not be triggered and the engine won’t cool. The purpose of the fan switch is ...