P0533 – AC refrigerant pressure sensor -high input

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By Benjamin Jerew (Contact Me)
Last Updated 2016-03-16
ASE Master Tech
CodeFault LocationProbable Cause
P0533 AC refrigerant pressure sensor -high input
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AC refrigerant pressure too high (cooling fault/incorrectly charged), wiring, AC refrigerant pressure sensor, ECM

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Table of Contents

  1. What Does Code P0533 Mean?
  2. What are the common causes of code P0533 ?
  3. What are the symptoms of code P0533 ?
  4. How do you troubleshoot code P0533 ?
  5. Codes Related to P0533
  6. Get Help with P0533

What Does Code P0533 Mean?

The air conditioning system keeps you cool in the summer and keeps your windows fog-free year-round. The air conditioning system can simply be described as a heat pump, removing heat from inside the vehicle and transferring it outside the vehicle, using a system of fans, radiators, and a compressor. The key to this heat-pumping capability is the refrigerant, typically R-134a, which circulates throughout the system via a series of tubes and hoses. The compressor charges the high side of the system, as far as the expansion valve, where the refrigerant rapidly expands, vaporizing and absorbing heat in the evaporator, which is inside the passenger compartment. The heated refrigerant, on the low side of the system now, travels to the condenser, outside the passenger compartment, where it releases that heat to the atmosphere, and then returns to the compressor, continuing the cycle.

The high side and low sides of the system are separated by the compressor and the expansion valve. Under normal operation, refrigerant pressure usually ranges from 190 psi to 240 psi, on the high side, and 20 psi to 35 psi, on the low side, depending on system design, atmospheric conditions, and driver demand. The engine control module (ECM) monitors one or more refrigerant pressure sensors to cycle the belt-driven air conditioning compressor clutch and gauge system performance.

In case the ECM detects that refrigerant pressure is too low or too high, it will lock out air conditioner function to protect the compressor and the rest of the system from damage. Based on the voltage from the refrigerant pressure sensor, in case the ECM calculates it abnormally high, typically over 350 psi, it will lock out the compressor clutch and store a diagnostic trouble code (DTC) in memory, DTC P0533, “A/C Refrigerant Pressure Sensor Circuit High Input.”

What are the common causes of code P0533 ?

DTC P0533 may have number of causes. Here are some of the most common.

  • System Overcharged – So-called A/C system “top-off kits,” even those with a pressure gauge, may not be accurate, resulting in incorrect system charging, possibly even damage.
  • Faulty Pressure Sensor – While not prone to damage or defect, internal faults can lead to an internal short-circuit.
  • Faulty Wiring – A short-to-power can send up to 5 V reference back to the ECM, on the signal line, skewing pressure calculations or falsely reporting overpressure in the system.
  • Moisture in System – If enough free moisture is present in the system, it could freeze and block the expansion valve. The air conditioning system may work properly for a few minutes, then suddenly spike pressure on the high-side, leading to an overpressure condition.

What are the symptoms of code P0533 ?

Depending on the vehicle, the check engine light (CEL) may or may not be illuminated, since P0533 is not an emissions-related DTC, but air conditioning will not work until the problem is fixed. Depending on the vehicle, you may note a message on the multi-information display or similar, or a blinking A/C light on the HVAC control stack. Some vehicles will reset the system when the engine is turned off, and the DTC may or may not be erased at that time. The next time the vehicle is started again, and A/C is requested by the driver, the system will usually retest itself. If the over-pressure over-voltage condition is still present, the ECM will simply lock out compressor function again and set the DTC.

How do you troubleshoot code P0533 ?

When it comes to diagnosing the air conditioning system, typically the first step is to verify refrigerant pressure, which requires the use of manifold gauges. Care must be taken to connect the gauges properly to avoid refrigerant loss and air pollution, not to mention skin and eye damage. Gloves and safety glasses are suggested.


  • With the engine off, measure refrigerant pressure. A good rule of thumb for measuring refrigerant pressure on a static system is 1 psi per 1 °F ambient temperature, that is, on a 75 °F day, you should measure about 75 psi. If you measure significantly higher or lower, you could have air in the system or an overcharged system, or a refrigerant leak or undercharged system.
  • With the engine off, both high-side and low-side readings should be the same. If you measure significantly higher or lower pressure on either side of the system, this may indicate a blockage, such as a collapsed or kinked refrigerant line, stuck expansion valve, or debris.
  • If the problem seems intermittent, this could be related to moisture in the system, freezing at the expansion valve. In this case, the air conditioning system may work properly for a few minutes, then suddenly spike pressure on the high-side, prompting the ECM to lock out the compressor. After shutting the vehicle off and enough time passes for the ice to melt, the system may work properly for a short time, until the expansion valve freezes again.

If your vehicle has any problems with refrigerant pressure, damaged lines, leaks, moisture, or blockage, you may need to consult a professional, as recover-recycle-recharge machines are expensive and not available to the public. Once you have confirmed proper refrigerant pressure, you can proceed with pressure sensor diagnosis. You will need an EWD (electrical wiring diagram) and repair manual, specific to your vehicle, and a DVOM (digital volt-ohm meter) to check the pressure sensor and circuit.

  • Check the electrical connector on the refrigerant pressure sensor for corrosion, bent pins, or other damage. Repair as needed.


  • With the key on and engine off, three-pin sensors will have a 5 V reference, ground, and signal wires. Check that you have good voltage and ground, then check the signal voltage against the chart. Most signal voltage will increase with pressure, about 1 V per 100 psi. If we measure 75 psi in the system, then we should read about 0.75 V on the signal line.
    • If you measure 5 V reference and 5 V signal, you have a short to power, which could be anywhere from the ECM to the pressure sensor. Disconnect the ECM and pressure sensor and check for short circuit in the harness.
      • If the short is in the wire harness or one of the connectors, repair as needed.
      • If the wire harness is sound, reconnect the ECM, but not the pressure sensor. Turn the key on. If the code returns, suspect a shorted ECM. If a different code comes back, most likely P0352, then suspect a shorted pressure sensor.
  • DTC P0531 A/C Refrigerant Pressure Sensor Performance
  • DTC P0532 A/C Refrigerant Pressure Sensor Circuit Low Voltage
  • DTC P0533 A/C Refrigerant Pressure Sensor Circuit High Voltage

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