Technical Description of OBD-II Trouble Code
High Circuit for A/C Evaporator Temperature Sensor
What does that signify?
This is a generic diagnostic trouble code (DTC) that is applicable to OBD-II vehicles. This includes vehicles 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.
In essence, the air conditioning evaporator functions 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 A/C evaporator temperature sensor plays a crucial role in the proper functioning of your HVAC (Heating, Ventilation, and Air Conditioning) system. The ECM (Engine Control Module) uses electrical values from this sensor to adjust the temperature inside according to your needs, in coordination with the evaporator and other A/C components.
The ECM triggers the P0538 code and associated codes (P0535, P0536, P0537, and P0539) 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 either mechanical or electrical in nature. Always consider the sensor’s environment, as it may be exposed to unique issues.
The P0538 code is set when the ECM detects an unexpectedly high electrical condition within the A/C evaporator temperature sensor or its circuit(s).
Photo of one type of evaporator temperature sensor:
What is the severity of this DTC?
Considering that your entire HVAC system was designed to enhance human comfort, the severity of this issue is set to the lowest possible level. A complete malfunction of the HVAC system poses virtually no threat to your safety. However, if you value comfort, it is advisable to address this problem promptly.
What are some of the symptoms of the code?
Symptoms of a P0538 trouble code may include:
What are some of the common causes of the code?
Possible causes for this P0538 code include:
What are some P0538 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. You may be able to access it by looking under the dash. However, you may need to remove various plastic panels and/or the radio, so always refer to your service manual for the exact location. Look for signs of overheating and/or corrosion on the sensor itself, as this may indicate a problem. If the sensor is found to be defective, replace it.
TIP: Ensure that the interior is at a reasonable temperature. Attempting to pry on cold plastic may cause it to break, so exercise caution.
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 how this works can provide insight into diagnosing the sensor. Typically, the manufacturer specifies desired resistance values at certain temperatures. Using a multimeter, you can measure the resistance within the sensor and compare it to the manufacturer’s specified values. If an open circuit is present, there may be internal resistance within the sensor, necessitating replacement.
NOTE: Your manufacturer may have a specific diagnostic strategy depending on the type of sensor, make, model, etc., so always refer to your service manual. If you are uncomfortable with electrical testing or working around 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 obvious signs of damage. Pay particular attention to areas where the wiring may be interfered with by the driver and passengers’ feet (if accessible).
