Technical Description of OBD-II Trouble Code
Intermittent Circuit Issue with A/C Evaporator Temperature Sensor
What does that signify?
This is a generic diagnostic trouble code (DTC) that is applicable to OBD-II vehicles, including those from Ford, Chevrolet, Dodge, Ram, and others. While it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
The air conditioning evaporator operates in the opposite manner of a condenser. The condenser converts gas to fluid, while the evaporator converts fluid to gas and absorbs heat from the fan air passing through it.
Its purpose is to remove heat from the air inside the cabin, thereby reducing the temperature inside the car. The proper functioning of the A/C evaporator temperature sensor is crucial for the HVAC (Heating, Ventilation, and Air Conditioning) system to operate correctly. The ECM (Engine Control Module) uses electrical values from this sensor to adjust the temperature inside the vehicle according to the user’s needs, in coordination with the evaporator and other A/C components.
The ECM triggers the P0539 code and associated codes (P0535, P0536, P0537, and P0538) when it detects an electrical range condition outside the desired range within the A/C evaporator temperature sensor or its circuits. This condition could be due to a mechanical or electrical problem. It is important to consider the sensor’s environment, as it may be exposed to unique issues.
The P0539 code is set when the ECM detects an intermittent malfunction within the A/C evaporator temperature sensor or its circuits.
Photo of one type of evaporator temperature sensor:
What is the severity of this DTC?
Considering that the entire HVAC system is designed to enhance human comfort, the severity of this code is set to the lowest possible level. A complete malfunction of the HVAC system poses virtually no threat to safety. However, if you value comfort, it is recommended to address this problem promptly.
What are some of the symptoms of the code?
Symptoms of a P0539 trouble code may include:
What are some of the common causes of the code?
Possible causes for this P0539 code may include:
What are some P0539 troubleshooting steps?
It is recommended to check for technical service bulletins (TSBs) specific to your vehicle. Accessing a known fix can save time and money during diagnosis.
Basic Step #1
Locate and visually inspect the A/C evaporator temperature sensor. Generally, the evaporator core is situated inside the HVAC (heating ventilation and air conditioning) air box. The A/C Evaporator Temperature sensor is typically mounted on or near the evaporator. It may be easily accessible by looking under the dashboard. However, it may be necessary to remove plastic panels and/or the radio, so always refer to the service manual for the exact location. Look for signs of overheating or corrosion on the sensor, as this may indicate a problem. If the sensor is found to be defective, it should be replaced.
TIP: Ensure that the interior of the vehicle is at a reasonable temperature. Applying force to cold plastic may cause it to break, so caution is advised.
Basic Step #2
Test the temperature sensor. In most cases, these sensors are of the resistor type, meaning that the resistance within the sensor changes in direct relation to the temperature. Understanding this principle can provide insight into diagnosing the sensor. Typically, the manufacturer specifies desired resistance values at certain temperatures. Using a multimeter, the resistance within the sensor can be measured and compared to the manufacturer’s specified values. If an open circuit is detected, there may be internal resistance within the sensor, necessitating replacement.
NOTE: The manufacturer may have a specific diagnostic strategy depending on the type of sensor, make, model, etc., so always refer to the service manual. If you are uncomfortable with electrical testing or working with refrigeration systems, it is advisable to take your vehicle to a reputable shop.
Basic Step #3
Inspect the wiring. Due to the location of the evaporator temperature sensor, it may be easy to locate and follow the harness to check for any visible signs of damage. Pay particular attention to areas where the wiring may be interfered with by the driver and passengers’ feet (if accessible).
