P1433

What Does Code P1433 Mean?

Diagnostic Trouble Code (DTC) P1433 signifies an electrical fault within the A/C Refrigerant Temperature Sensor Circuit, specifically indicating a low voltage condition. The Engine Control Module (ECM) or Powertrain Control Module (PCM), often in conjunction with the HVAC control module, monitors the electrical signal from the A/C refrigerant temperature sensor. This sensor typically provides a voltage signal proportional to the refrigerant temperature, often located at the evaporator outlet or within the accumulator/receiver-drier, depending on the vehicle manufacturer and system design. A “circuit low” condition means the voltage detected by the monitoring module is consistently below the specified operational threshold, or very close to zero volts. This can be interpreted by the control module as an open circuit, a direct short to ground, or a severely malfunctioning sensor. To prevent damage to the A/C compressor or to maintain system integrity, the control module may disable the A/C compressor clutch operation upon detection of this fault, limiting or preventing the air conditioning system from producing cold air.

Common Symptoms

• A/C system blowing warm air or no cold air.
• A/C compressor clutch fails to engage.
• Malfunction Indicator Lamp (MIL) or “Check Engine” light illuminated on the dashboard.
• Blower motor operates, but only ambient air is discharged through the vents.
• Inconsistent or inefficient cooling performance from the A/C system.

What Causes the Code P1433?

• Faulty A/C Refrigerant Temperature Sensor: The sensor itself may have an internal electrical short, an open circuit, or significantly degraded performance, leading to a consistently low voltage output.
• Wiring Harness Issues:
  • Short to Ground: The signal wire from the sensor may be chafed or damaged, causing it to contact a grounded surface.
  • Open Circuit: A complete break in the signal wire, or in the power/ground supply wires to the sensor.
  • Excessive Resistance: Corrosion or damage within the wiring can create high resistance, leading to a voltage drop and a “low” signal at the control module.
• Corroded or Loose Electrical Connections: Poor pin tension, corrosion, or contamination at the sensor’s electrical connector or at the control module’s connector can disrupt the circuit integrity.
• Faulty HVAC Control Module or PCM: Although less common, an internal fault within the monitoring module’s input circuit can cause it to misinterpret the sensor’s signal as low.
• Incorrect Sensor Installation: If a wrong or incompatible A/C refrigerant temperature sensor was previously installed.

How to Diagnose and Troubleshoot

A systematic diagnostic approach is crucial for accurately identifying the root cause of P1433.

1. Verify DTC and Freeze Frame Data: Connect an OBD-II scanner to the vehicle’s Data Link Connector (DLC). Confirm P1433 is present and check for any related or pending codes. Analyze freeze frame data, which provides a snapshot of engine and sensor parameters at the moment the fault was set. This context can be invaluable. Clear the DTC and attempt to replicate the fault by operating the A/C system.
2. Visual Inspection:
   • Locate the A/C refrigerant temperature sensor. Its exact location varies but is often found threaded into or clamped onto an A/C line near the evaporator, or integrated into the accumulator/receiver-drier.
   • Thoroughly inspect the sensor’s electrical connector and the adjacent wiring harness for any signs of damage, chafing, cuts, corrosion, or loose connections. Pay close attention to areas where the harness might rub against engine components or sharp edges.
   • Verify proper routing and secure mounting of the harness.
3. Test Sensor Reference Voltage and Ground:
   • With the ignition in the RUN position (engine OFF), disconnect the A/C refrigerant temperature sensor.
   • Using a Digital Multimeter (DMM), measure the voltage between the sensor’s power supply wire terminal and a known good chassis ground. Verify the presence of the specified reference voltage (typically 5V, but some systems may use 12V). Refer to the vehicle’s wiring diagram for exact specifications.
   • Next, measure the resistance between the sensor’s ground wire terminal and chassis ground. It should read very low resistance (near 0 ohms), indicating a good ground connection.
4. Test Sensor Signal Circuit Continuity and Shorts:
   • With both the sensor and the relevant control module (PCM/HVAC) disconnected, use the DMM in resistance mode to check for continuity between the signal wire terminal at the sensor connector and its corresponding pin at the control module connector. Resistance should be very low, indicating good continuity.
   • While still disconnected, check for shorts to ground on the signal wire by measuring resistance between the signal wire terminal and chassis ground. Resistance should be infinite (open circuit).
   • Check for shorts to voltage by measuring resistance between the signal wire terminal and the power supply wire terminal. Resistance should be infinite.
5. Test A/C Refrigerant Temperature Sensor Resistance/Output:
   • Most A/C refrigerant temperature sensors are thermistors, meaning their internal resistance changes with temperature. With the sensor disconnected, measure its resistance across its terminals using the DMM.
   • Compare this reading to the manufacturer’s specifications for ambient temperature. You may need to gently warm or cool the sensor (e.g., with a heat gun or ice water, carefully) and observe if the resistance changes smoothly and within specified parameters. A sensor with an internal open circuit will show infinite resistance, while a shorted sensor will show very low or zero resistance. Both would lead to a “circuit low” condition if the module expects a higher voltage.
   • If accessible, back-probe the signal wire with the sensor connected and ignition ON. Monitor the voltage output. A healthy sensor typically outputs a voltage within a specified operating range (e.g., 0.5V to 4.5V). A consistently low voltage (e.g., near 0V) confirms the circuit low condition from the sensor’s perspective.

Recommended Repairs and Solutions

Once the faulty component has been precisely identified through diagnostic procedures, the appropriate repair can be executed:

• Replace the A/C Refrigerant Temperature Sensor: If diagnostic tests confirm the sensor itself is faulty (internal short, open, or out-of-spec resistance/voltage output), replace it with a new OEM or equivalent quality part. Be aware that some sensors are exposed to refrigerant and may require the A/C system to be evacuated and recharged by a certified technician; others are external and simply measure line temperature. Always follow manufacturer’s torque specifications for threaded sensors.
• Repair or Replace Damaged Wiring: If the wiring harness is found to be shorted, open, or has excessive resistance, repair the specific damaged section. Use proper automotive-grade wiring, solder connections, and insulate with heat-shrink tubing. Ensure the repaired section is routed securely to prevent future damage. If damage is extensive or involves multiple wires, replacing the entire harness section may be more reliable.
• Clean and Secure Electrical Connectors: If corrosion or poor terminal tension is identified, clean the connector terminals using an appropriate electrical contact cleaner and a small brush. Carefully adjust pin tension if necessary. Apply a small amount of dielectric grease to prevent future corrosion and ensure a secure connection.
• Address Control Module Faults: If all sensor and wiring integrity tests pass, and the P1433 code persists, the fault may lie within the HVAC control module or PCM. This is a less common scenario and typically requires professional diagnosis and replacement, often followed by programming or coding the new module to the vehicle.
• Clear DTCs and Verify Repair: After any repair, clear all stored DTCs using an OBD-II scanner. Perform a comprehensive test drive under varying conditions, specifically operating the A/C system, to confirm that the P1433 code does not return and that the A/C system functions correctly.