Fix P0533: Mechanic’s solutions that WORKED

The P0533: A/C Refrigerant Pressure Sensor Circuit High Input code indicates a problem with the A/C refrigerant pressure sensor circuit, specifically a high input signal. This sensor is responsible for monitoring the pressure of the refrigerant in the air conditioning system. When the sensor detects a voltage reading higher than expected, it triggers this fault code.

P0533 quick overview

Meaning	P0533: A/C Refrigerant Pressure Sensor Circuit High Input
Is it serious?	This code is not typically serious on its own, but it can affect the functionality of your vehicle’s air conditioning system. It may result in reduced cooling performance.
Possible causes	– Faulty A/C refrigerant pressure sensor – Damaged or disconnected wiring related to the sensor – High refrigerant pressure due to overcharging or other issues – Sensor circuit issues, including corrosion or poor connections – Environmental factors affecting sensor readings
How to diagnose?	Check A/C Refrigerant Pressure Sensor Location: Locate the A/C refrigerant pressure sensor, often found near the A/C compressor or in the A/C line. Inspect Wiring and Connectors: Examine the sensor’s wiring and connectors for damage, loose connections, or corrosion. Verify Refrigerant Pressure: Use a gauge to measure the refrigerant pressure in the A/C system. Ensure it is within the recommended range. Check Sensor Condition: Inspect the condition of the A/C refrigerant pressure sensor itself to ensure it’s not damaged. Replace Sensor if Faulty: If the sensor is found to be faulty or if there are wiring issues, consider replacing it with a compatible replacement. Clear Diagnostic Codes: After any repairs or replacements, use a diagnostic tool to clear the fault code and monitor if it returns.

How to fix P0533 – learn from mechanics

I looked into P0533 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Honda

Vehicle Information: 2009 Honda Accord EX-L 3.5L

Issue + Repair History: The car had a problem with the A/C compressor not engaging and a Check Engine Light (CEL) on. Codes P0135, P0155, P0533 were present. The customer reported that disconnecting the battery would temporarily fix the issue.

Other OBD2 Codes + Test Results: P0135, P0155 (O2 Sensor Heater Circuit), P0533 (A/C Pressure Sensor High Input)

Suggestions to Fix Issue:

• Check the A/C pressure sensor signal and wiring.
• Investigate the relay for the clutch.
• Inspect the PGM-FI subrelay A.
• Look for commonality in grounds between the air-fuel ratio sensors and the A/C pressure sensor.

Final Fix: The issue was resolved after identifying pinched wires behind the right headlight from a previous accident. The damaged wires affected the O2 sensor heaters and the vent valve code. The FI relays were also implicated. After repairing the wiring, the problem was resolved.

Case #2: Ford

Vehicle Information: 2008 Ford Fusion SE 2.3L

Issue + Repair History: Vehicle came in with a replacement engine due to lack of oil. The cooling fan was running at high speed constantly with the engine running. Vehicle had code P0533, suspected to be due to low refrigerant. After replacing the PCM and the cooling fan module, the issue persisted.

Other OBD2 Codes + Test Results: P0533 (A/C Refrigerant Pressure Sensor Circuit High Input)

Suggestions to Fix Issue:

• Check Engine Coolant Temperature (ECT) data and A/C data for unusual readings.
• Focus on resolving the P0533 code.
• Check wiring and grounds for the cooling fan and A/C system.
• Inspect A/C Pressure Sensor signal and wiring.

Final Fix: The problem was traced back to the A/C transducer (pressure switch) sending a high pressure signal to the PCM, causing the fan to run at high speed. The transducer was corroded, leading to incorrect readings. Replacing the transducer resolved the issue, and the cooling fan operated normally.

Case #3: Chrysler

Vehicle Information: 2007 Chrysler Sebring Limited 2.4L

Issue + Repair History: The car arrived from a used car dealer with an inoperative A/C system. Scanning revealed code P0533. The pressure sensor was replaced, but the compressor still wouldn’t engage. The original compressor seemed disengaged, while a replacement compressor appeared to be engaged constantly.

Other OBD2 Codes + Test Results: P0533 (A/C Refrigerant Pressure Sensor Circuit High Input)

Suggestions to Fix Issue:

• Run diagnostic tree to ensure wires are not shorted to voltage.
• Understand that the compressor is a clutchless variable displacement compressor with a swash plate controlling it internally.
• Check the wiring and connector of the compressor.

Final Fix: After understanding the operation of the clutchless variable displacement compressor, the replacement compressor was installed, resolving the issue with the A/C system.

Case #4: Saturn

Vehicle Information: 2002 Saturn L300 3.0L

Issue + Repair History: The car had the SES and wrench lights on, with no A/C operation. Scan data indicated a ground issue with all four sensors, and there was no ground coming from the ECM to these sensors. The ground would disappear when the key was cycled on.

Other OBD2 Codes + Test Results:

P1283 – APP Sensor 2 Circuit High Voltage

P0453 – EVAP Fuel Tank Pressure Sensor Circuit High Voltage

P0463 – Fuel Level Sensor Circuit High Voltage

P0533 – A/C Refrigerant Sensor Circuit High Voltage

Suggestions to Fix Issue:

• Check the grounds and connectors at the splice pack, which is located about midway across the rear valve cover and the left instrument panel fuse block.
• Replace the ECM and program it.
• Check for a single ground wire from the splice pack to the ECM (located on pin 62 of the J1 connector).

Final Fix: After checking the grounds and connectors at the splice pack and finding no issues, the ECM was replaced and programmed. This resolved the issue, and all sensors came back online, restoring the A/C operation. The use of a single ground wire from the splice pack to the ECM raised concerns, but this approach was followed. Additionally, a P1780 TCM request code was encountered after programming the ECM, but it was cleared, and the MIL light went out.

Case #5: Dodge

Vehicle Information:

• 2005 Dodge Ram 3500 SLT
• Engine: 5.9L

Issue + Repair History:

• The vehicle had a problem with the fan speed on first start, whether hot or cold. The high-side psi (pressure) would go over 400 psi, causing the A/C to shut down.
• When a scanner was hooked up, both fan speed and % control remained at zero, with no change regardless of what was done.

Repair Steps Taken:

• The wiring harness was run, and a bad fuse panel was discovered. Power was going into the fuse and out of the fuse but was not making it out of the fuse box. This issue was fixed.
• After fixing the fuse panel problem, command from the computer for % control with A/C on was observed. However, there was no RPM signal from the fan.
• The next step was to replace the fan clutch.

Related Repair History: Before this issue, the truck came in with a drive belt coming apart and damaging the high-side A/C hose. The hose and belt were repaired.

Computer Codes + Descriptions:

• P0480 – Fan Control 1 Control Circuit
• P0483 – Fan Speed
• P0533 – A/C Pressure High
• P0243 – Wastegate
• P2509 – ECM/PCM Power Supply Intermittent

Final Fix: The problem with the fan speed and A/C high-side pressure was traced to a faulty fuse (#36) that was not supplying power to the fan clutch. The solution involved replacing both the fuse panel and the fan clutch.

Advice	Diagnostic Step Description
Check the A/C Pressure Transducer	Verify the functionality of the A/C pressure transducer, which commands the high and low fans.
Inspect Wiring Harness for Issues	Examine the wiring harness for any faults, such as damaged or corroded wires, that may affect sensor readings.
Verify Fan Clutch Functionality	Ensure that the fan clutch is operating correctly, as a faulty clutch can lead to high A/C pressure.
Check Fuse Panel for Power Distribution	Inspect the fuse panel for proper power distribution to components like the fan clutch, and replace any faulty fuses or panels.
Review TSBs (Technical Service Bulletins)	Check for relevant manufacturer TSBs that may address known issues related to the fault code.