P0537 OBD-II Trouble Code: A/C Evaporator Temperature Sensor Circuit Low

P0537 A/C evaporator temperature sensor circuit low definition

A P0537 code indicates that the Powertrain Control Module (PCM) has stored voltage readings from the A/C evaporator temperature sensor that are outside of normal parameters, triggering a trouble code.

What the P0537 code means

The temperature switch in an automotive A/C system is mounted in the evaporator core’s fins and is of a capillary design. When the evaporator core’s temperature drops, the capillary pressure in the switch drops, lowering circuit resistance and increasing the voltage input signal to the PCM. The PCM sees this as a change in temperature and cycles the compressor clutch on and off. A trouble code is registered when these voltage fluctuations are at odds with the reference limit. Usually three failure cycles are necessary before the PCM will store a code and illuminate the Malfunction Indicator Lamp (MIL).

What causes a P0537 code?

• Failed evaporator temp sensor
• Failed expansion valve, resulting in freeze up of evaporator core
• Damaged or shorted wiring
• Overcharged A/C system
• Low refrigerant condition
• Faulty climate control head unit

What are the symptoms of a P0537 code?

• Inoperative A/C system
• Stored code, illuminated MIL
• Air conditioning “ON” indicator lamp (on A/C switch) flashes repeatedly
• Freeze up of evaporator case, with condensate dripping onto floor

How does a mechanic diagnose a P0537 code?

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 necessary for this diagnosis and repair.

• Begin 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 condition, connect the scanner/code reader to the diagnostic port. Record all stored codes and freeze frame data.

• Test drive the vehicle to see if the code returns. If not, the problem may be an intermittent condition. Intermittent conditions can be difficult 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 blower on its highest setting, with A/C on Max. Observe gauge readings and compare to factory specs, making adjustments in refrigerant level as needed. Turn the blower speed to Low and observe gauges for pressure readings.

• If system’s low-side pressure falls too much – below 25 PSI or so – it can cause a freezeup 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 (unplug the sensor first)

• Compare your numbers 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. Do a resistance/continuity test on the evaporator temperature sensor circuit. Repair/replace any shorted or open wiring as needed. If the evaporator temperature sensor and circuits test as good, suspect the head unit itself or the A/C compressor switch.

• Test unit, compare to factory specs and replace components as needed.

Common mistakes while diagnosing P0537 code

Often, with a P0537 code, technicians or owners overfill their vehicles’ systems with refrigerant, resulting in problems. It’s important to know 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, often lead to a catastrophic failure.

How serious is a P0537 code?

Operating the A/C system with a P0537 code can lead to failure of components and further problems.

What repairs can fix a P0537 code?

• Replacement of evaporator core temperature sensor
• Replacement of expansion valve
• Addition of refrigerant
• Replacement/repair of wiring or A/C/climate control head unit

Addition comments for consideration for P0537 code

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 just add refrigerant if a P0537 code is registered. Make sure you’ve found the root cause of the P0537 code before going any further.

Need help with a P0537 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.