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Error Code P0539 is defined as A/C Evaporator Temperature Sensor Circuit Intermittent, which means the A/C evaporator temperature sensor has either too high or too low voltage signal, a problem usually caused by faulty evaporator sensor.
This code is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially vehicles made since 1996 up to present. This includes but not limited to Chevrolet, Dodge, Ford, Ram, etc. Though generic, specific steps may vary depending on the make, model, year, and powertrain configuration of the vehicle.
The A/C evaporator works in the opposite sense as the condenser. The former converts gas to fluid, while the former converts fluid to gas while absorbing heat from the fan air which flows through it in the process.
The purpose of which is to remove the heat from the air inside the cabin and reduce the temperature inside the vehicle. The A/C evaporator temperature sensor plays an important role in the proper operation of the HVAC (Heating Ventilation and Air Conditioning) system. The PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) uses electrical values from this sensor to adjust the temperature according to your needs, alongside with the evaporator among the A/C components.
Error Code P0539 is set when the PCM detects an intermittent condition, which is a malfunction within the A/C evaporator temperature sensor circuit(s).
Other related error codes include:
- Error Code P0535
- Error Code P0536
- Error Code P0537
- Error Code P0538
As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other noticeable symptoms include:
- Erratic or fluctuating fan air temperature
- No cold air coming from the vents
- A/C compressor clutch not engaging
- Malfunctioning HVAC system
The most common cause of this code is defective evaporator temperature sensor. Other potential causes include:
- Defective expansion valve (leads to freezing up of evaporator core)
- Open, short, corroded or damaged electrical components
- Wiring harness connector issue
- Overcharged A/C system
- Insufficient refrigerant levels
- Defective climate control head
How to Check
As with most error codes, make sure you check with the TSB (technical service bulletin) to get access to known fix for common repairs. This will save you time and money for diagnosis and repairs.
Find the A/C evaporator temperature sensor and inspect it thoroughly. Generally, this is located inside the HVAC air box. The sensor is mounted to the evaporator itself, if not very near it. Usually, you can get access to it by simply looking under the dash. In some cases though, you may need to remove many plastic panels and radio, so it’s best to refer to your service manual for the specific location. Also, make sure you keep an eye for any signs of overheating or corrosion from the sensor itself. This almost always means a problem. If you find it defective, then replace the sensor.
Tip: Make sure you check the temperature of the interior. It should be at a reasonable level before working. Prying on cold plastic could cause it to break easily.
Test the temperature sensor. Many times, these are resistor type sensor, which means the resistance within the sensor changes in direct relation to the temperature. Understand how this works, so you have a good idea of how to diagnose the sensor itself. In most cases, the manufacturer will have a desired resistance at certain temperatures.
Use a multimeter to record the resistance within the sensor, and compare it to the desired values set by the manufacturer. If there is an open condition, that means you may have an internal resistance within the sensor, which must be replaced.
Note: Vehicle manufacturers provide specific steps for diagnosis depending on which type of sensor, make, model, etc., so again, check your service manual. If still unsure, then you’ll be better off asking the services of a reputable shop with certified refrigeration system technician.
Check the wiring and located the evaporator temperature sensor. If can be easy to located and follow the harness, so check for any obvious signs of damages too, especially around the driver and passenger’s feet. Wirings interference is common in that area. Fix and replace components accordingly.
How to Fix
Depending on your diagnosis, common repairs for this code include:
- Replacement of the A/C evaporator temperature sensor
- Replacement of damaged or faulty connectors, wires, fuses, or harnesses
- Replacement of the expansive valve
- Replacement of the climate control head unit
- Adding refrigerant
The most common mistake in dealing with this code is assuming it’s a case of insufficient refrigerant, which can lead to adding more to the vehicle that still has enough. This can result in serious damage. Thus, a thorough diagnosis is very important.
A vehicle with this code is still drivable, but the A/C will not work efficiently, or not work at all.