So a bad coolant temp sensor can cause drivability issues, increased fuel consumption and increased engine wear. It will also likely mean that the coolant temperature gauge (if it has one, many cars now only have idiot lights) doesn't work.
3 Symptoms of temperature sensor and thermocouple errors
The symptoms of temperature sensor and thermocouple errors can differ depending on the type and severity of the issue. However, erratic or inconsistent readings, out-of-range or unrealistic readings, and no readings or signal loss are common signs.
To check if a temperature sensor is working, first, compare its readings with a known accurate thermometer. This helps ensure the sensor's accuracy. Place both in the same environment and see if the readings match. Next, monitor the sensor for consistent readings in stable conditions.
If your AC shows irregular temperatures, where sometimes it's much cooler than other times, this can indicate AC sensor malfunction. This, in turn, will lead to AC sensors needing replacement.
A malfunctioning sensor might cause the AC unit to cycle rapidly or continuously. This is because the sensor fails to detect the actual temperature accurately, leading to frequent on-off cycles, which can wear out the system and increase energy consumption.
It's not recommended to unplug the coolant temperature sensor unless necessary for diagnostic purposes, as it can adversely affect engine operation and potentially cause damage if left unplugged for an extended period.
Incorrect Temperature Gauge Reading
If the gauge or indicator reading is off by more than a few degrees, then the sensor is likely faulty.
A faulty temperature sensor could misread the temperature in the evaporator unit. Your unit will keep turning off and on at random intervals, which can result in premature failure.
Coolant temperature sensors are resistors and can't be reset. The engine control unit is the part that actually runs software and just takes information from the sensor. If you think you have a problem with your sensor, test its resistance by attaching it to a multimeter and submerging the sensor in hot water.
If it's easy to get to, “Replacing a coolant temperature sensor is generally considered a relatively straightforward job for someone with basic mechanical skills and the right tools,” says Knoll.
While there is a small chance that there is an issue with the running temperature of your engine, by far the most common issue with trouble code P0128 is a faulty thermostat. The exact location of the thermostat and issues related to a damaged thermostat may vary depending on your vehicle.
Test it with a multimeter on the 10,000 ohms scale,if it's not in the hundreds of ohms when the engine is warmed up then it's faulty,the same goes if it's not 1k Ohms or more when the engine is dead cold.
If your coolant temperature sensor is failing or has failed, do not continue driving your vehicle. You should get it fixed right away. A faulty sensor can lead to overheating. This will cause damage to your engine as well as other components, which will be very expensive to fix.
If the 'Check Engine' light suddenly comes on, this could imply a hitch with the coolant temperature sensor. If the computer detects an unsavory development with the sensor's circuit or signal, it may set off the 'Check Engine' light. And the light will not go off until a specialist readily addresses the issue.
In short, an air conditioning system cannot function properly without a sensor. AC sensors are vital for accurate temperature detection and control. Without them, the AC unit would not be able to gauge the indoor temperature or adjust its cooling output accordingly.
Temperature fluctuations. Incorrect temperature readings. Blower motor broken or cold air for only a short time (in car A/C systems with thermistors)
To test a temperature sensor with a multimeter, set it to measure resistance, clip one probe to an outer sensor connector and the other across from it. Submerge in hot then ice water, note readings after a few seconds - around 250 and 1000 ohms respectively.
INTAKE-AIR TEMPERATURE SENSOR FAULTY: SYMPTOMS
Fault code is stored, engine indicator lamp may come on. Problems starting. Reduced engine power. Increased fuel consumption.
The AC sensor on your thermostat is located near the evaporator coils. Indoor air moving toward the return vents passes by the sensor and coils. In turn, the sensor reads the temperature and checks if it matches what you've set on the thermostat.