P0539 OBD-II Trouble Code: A/C Evaporator Temperature Sensor Circuit Intermittent

P0539 code definition

When the Powertrain Control Module (PCM) detects a voltage reading from the A/C evaporator temperature sensor that lies outside of the specifications as set by the manufacturer, a P0539 trouble code is stored. Some additional related trouble codes include a P0535, P0536, P0537, and P0538 code.

What the P0539 code means

A variation of either too high or low in the voltage signal coming from the A/C evaporator temperature sensor causes the storage of a P0539 trouble code and the Check Engine light to illuminate.

What causes the P0539 code?

A faulty evaporator temperature sensor is usually the source of the storage of a P0539 trouble code. Some other reasons for the storage of the code include faulty electrical connections, damaged or shorted wiring, a faulty climate control head, a low refrigerant condition, an overcharged A/C system, or a faulty expansion valve causing the evaporator core to freeze up.

What are the symptoms of the P0539 code?

An inoperative A/C system is the most common symptom of a P0539 trouble code. Some other symptoms of this code include the A/C ON indicator flashing repeatedly or the evaporator case freezing up and dripping onto the floorboard of the vehicle.

How does a mechanic diagnose the P0539 code?

Diagnosing and repairing a P0539 trouble code requires a mechanic to have certain equipment, including an OBD-II scanner, digital volt/ohmmeter, and a set of air conditioning gauges. The mechanic should also perform the following when attempting to diagnose a P0539 trouble code:

• Visually inspect all wiring, connectors, and components.
• Connect the scanner to the diagnostic connector in order to download any stored trouble codes or freeze frame data. This information could come in handy with diagnosing the vehicle's problems, especially if the condition is intermittent.
• Clear the P0539 trouble code and test the system.
• If it returns, connect the A/C gauges to the proper fittings and turn the A/C on max and the blower on high. The mechanic should then compare any readings to the manufacturer's specifications.
• Next, after adding the required amount of refrigerant, the mechanic should turn the blower speed to low and compare the readings to the manufacturer's specifications.
• If the A/C system is operating normally, the mechanic should unplug the evaporator temperature sensor electrical connector and test the resistance of the sensor using the digital volt/ohmmeter.
• Clear the P0539 trouble code and retest the system to see if the trouble code returns.

Common mistakes when diagnosing the P0539 code

A common mistake made by mechanics when trying to fix a P0539 trouble code is to assume it is caused by a low refrigerant condition. The refrigerant is then overfilled by the mechanic, causing a catastrophic failure. To avoid this, vehicle owners should only have a qualified mechanic, with the proper tools, service the A/C system in their vehicle.

How serious is the P0539 code?

Fortunately, a P0539 trouble code is not that serious, with the most likely symptom a non-working A/C system or, at most, a wet floorboard.

What repairs can fix the P0539 code?

Repairing a P0539 trouble code requires the mechanic to perform certain steps, including:

• Replace any faulty or damaged wiring, connectors, or components.
• After testing the A/C with the A/C gauges hooked up and the A/C at max and the blower on high, fill the A/C with the appropriate amount of refrigerant.
• Replace the expansion valve if the A/C system is drawing too low of a pressure with the blower set to low.
• Replace the evaporator temperature sensor if it is bad.
• Replace the climate control head or A/C compressor switch if these components prove faulty after further testing.

Additional comments for consideration regarding the P0539 code

If, after diagnosing the evaporator temperature sensor or any related circuitry, the mechanic fails to find the source of the problem, the mechanic should suspect a faulty A/C compressor switch or climate control head. The mechanic needs to perform subsequent testing of these components to see if the problem lies there.

Need help with a P0539 code?

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