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P0538 is a diagnostic trouble code (DTC) for "A/C Evaporator Temperature Sensor Circuit High". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
A P0538 code indicates that the powertrain control module (PCM) has registered voltage readings from the A/C evaporator temperature sensor that are outside of norms, triggering a trouble code.
The temperature switch in an automotive A/C system is mounted in the fins of the evaporator core and uses a capillary design. When the evaporator core’s temperature drops, the capillary pressure in the switch drops as well. This lowers circuit resistance and increases the voltage input signal to the powertrain control module (PCM). The PCM registers this as a change in temperature and begins to cycle the compressor clutch on and off. A trouble code is registered when these voltage fluctuations differ from the reference limit. Usually three failure cycles are necessary before the PCM will store a code and illuminate the Malfunction Indicator Lamp (MIL).
An OBD-II code reader/scanner, digital volt/ohmmeter and a set of A/C gauges or A/C recycling machine with built-in gauges will be needed for a proper diagnosis and repair.
Begin your diagnosis by visually inspecting all wiring and connectors. Repair/replace any damaged, disconnected, corroded or shorted wiring, connectors and parts as needed. Retest the system.
If all wiring, connectors, parts and fuses appear to be in good working order, connect the scanner/code reader to the diagnostic port. Record any stored codes and freeze frame data.
Test drive the vehicle and re-test to see if the code returns. If not, the problem may be an intermittent condition. Intermittent conditions can be a challenge to diagnose correctly and may need to be allowed to worsen and return before a proper diagnosis can be made.
Connect A/C gauges to the proper fittings, start the engine and turn the A/C blower on its highest setting, with A/C on Max. Observe gauge readings and compare to factory specs, adding refrigerant level as needed. Turn the blower speed to Low, then observe gauges for pressure readings.
If system’s low-side pressure falls too much – below 25 psi or so – it can cause a freeze up of the evaporator and a trouble code. If this occurs, the expansion valve could be at fault.
If the A/C system operates normally, perform a resistance test on the evaporator temperature sensor’s electrical connector (after unplugging the sensor)
Compare your findings to factory specs, replace sensor if needed.
If evaporator temperature sensor seems to be within operating norms, disconnect the PCM electrical connector and electrical connector for the climate control head unit. Perform a resistance/continuity test on the evaporator temperature sensor circuit. Repair/replace any shorted or open wiring if indicated. If the evaporator temperature sensor and circuits test as good, suspect the climate control head unit itself or the A/C compressor switch.
Test unit, compare to factory specs and replace components as needed.
Often, with a P0538 code, technicians or owners overcharge their vehicles’ systems with refrigerant, resulting in problems. It’s important to make certain that it’s absolutely necessary to add refrigerant before moving forward, and only qualified personnel with the right tools/equipment should attempt this service. Single hose charging kits, with no gauge or an inadequate gauge, are often a recipe for trouble.
Operating the A/C system with a P0538 code can lead to further problems and failure of other components.
While the lines, O-rings and gaskets of an A/C system are porous and even a newer vehicle can lose 5 percent of its refrigerant over a year’s time, it’s important to not simply add refrigerant if a P0538 code is registered. Make sure you’ve found the root cause of the P0538 code before going any further. Note that the P0538 code indicates a high reading from the evaporator temperature sensor circuit, as opposed to the low reading of a P0537 code.
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