P1535 - A/C High Side Temperature Sensor Circuit

Introduction:

The P1535 diagnostic trouble code (DTC) signals an issue within the Air Conditioning (A/C) system, specifically related to the high side temperature sensor circuit. This sensor plays a crucial role in monitoring the temperature of the refrigerant in the high-pressure side of the A/C system, allowing the engine control unit (ECU) to make informed decisions regarding A/C compressor operation and overall system efficiency. Addressing a P1535 code promptly is essential for maintaining optimal A/C performance and preventing potential damage to other A/C components.

Table: P1535 - A/C High Side Temperature Sensor Circuit Details

Topic	Description	Potential Solutions
Definition	The P1535 DTC indicates that the Engine Control Unit (ECU) has detected a fault in the A/C high side temperature sensor circuit. This fault could be an open circuit, a short to ground, a short to voltage, or an out-of-range reading from the sensor. The ECU uses the high side temperature sensor reading to protect the A/C compressor from damage due to over-pressure and overheating, and to optimize A/C performance.	N/A (Definitional)
Symptoms	Reduced or no A/C cooling performance; A/C compressor not engaging; Intermittent A/C operation; Engine overheating (in some cases); Check Engine Light illuminated; A/C compressor clutch cycling rapidly (if it engages at all). The specific symptoms can vary depending on the vehicle and the nature of the fault.	N/A (Symptomatic)
Common Causes	Faulty A/C High Side Temperature Sensor; Wiring harness issues (damaged wires, corroded connectors, loose connections); Open or short in the sensor circuit; High resistance in the sensor circuit; Faulty ECU (rare); Refrigerant overcharge or undercharge (can cause abnormal temperature readings); A/C system blockage (leading to excessive pressure and temperature).	N/A (Causal)
Diagnostic Steps	Visual inspection of the sensor and wiring harness; Checking the sensor resistance with a multimeter; Testing the sensor circuit for voltage and ground; Performing a continuity test on the wiring; Inspecting the connectors for corrosion or damage; Using a scan tool to monitor the sensor readings; Comparing the sensor readings to the manufacturer's specifications; Checking the refrigerant level; Performing an A/C system pressure test.	N/A (Diagnostic)
Sensor Function	The A/C high side temperature sensor is a thermistor, meaning its resistance changes with temperature. As the refrigerant temperature increases, the sensor's resistance decreases. This varying resistance is read by the ECU as a voltage signal, which is then translated into a temperature reading. This reading is critical for the ECU to control the A/C compressor and prevent damage.	N/A (Functional)
Location	The A/C high side temperature sensor is typically located on the high-pressure line of the A/C system, usually near the condenser or the compressor. The exact location can vary depending on the vehicle make and model. Consult your vehicle's service manual for the specific location.	N/A (Locational)
Wiring Diagram Basics	The A/C high side temperature sensor circuit typically consists of two or three wires: a signal wire (carrying the voltage signal back to the ECU), a ground wire, and sometimes a 5-volt reference wire from the ECU. Understanding the wiring diagram for your specific vehicle is crucial for proper diagnosis and repair. Look for the sensor in the A/C section of the wiring diagram.	N/A (Wiring)
Tools Needed	Multimeter; Scan tool (capable of reading A/C system data); Wiring diagram for your vehicle; Basic hand tools (sockets, wrenches, screwdrivers); Wire stripper/crimper; Test light; Refrigerant manifold gauge set (for checking refrigerant levels and pressures).	N/A (Tools)
Related DTCs	P0530 (A/C Refrigerant Pressure Sensor Circuit Malfunction); P0532 (A/C Refrigerant Pressure Sensor Circuit Low Input); P0533 (A/C Refrigerant Pressure Sensor Circuit High Input); P0645 (A/C Clutch Relay Control Circuit); Any other DTC related to the A/C system or engine cooling system. These codes can provide additional clues about the underlying problem.	N/A (Related Codes)
Safety Precautions	Always disconnect the negative battery terminal before working on the electrical system. Be careful when working around the A/C system, as it contains high-pressure refrigerant. Wear safety glasses to protect your eyes. If you are not comfortable working on the A/C system, take your vehicle to a qualified technician. Refrigerant can cause frostbite if it comes into contact with skin.	N/A (Safety)

Detailed Explanations:

Definition: The P1535 DTC indicates that the Engine Control Unit (ECU) has detected a fault in the A/C high side temperature sensor circuit. This means the ECU is receiving an implausible signal from the sensor, or no signal at all. This can be due to a variety of electrical issues within the sensor circuit, or even a faulty sensor itself. The ECU uses this sensor data to manage the A/C system effectively and prevent damage to components.

Symptoms: The symptoms of a P1535 code can vary, but the most common is reduced or no A/C cooling performance. You might also notice that the A/C compressor is not engaging, or that it engages intermittently. In some cases, the engine might overheat because the A/C system is not functioning properly. The Check Engine Light will almost always be illuminated. The compressor clutch may cycle rapidly if it is engaging, due to the ECU trying to compensate for the faulty sensor reading.

Common Causes: The most common cause of a P1535 code is a faulty A/C high side temperature sensor. However, other potential causes include wiring harness issues, such as damaged wires, corroded connectors, or loose connections. An open or short in the sensor circuit can also trigger the code. High resistance in the sensor circuit can also cause problems. In rare cases, a faulty ECU can be the culprit. Refrigerant overcharge or undercharge can also cause abnormal temperature readings, leading to the code. Finally, a blockage in the A/C system can cause excessive pressure and temperature, triggering the code.

Diagnostic Steps: The first step in diagnosing a P1535 code is a visual inspection of the sensor and wiring harness. Look for any obvious signs of damage, such as cracked or broken wires, corroded connectors, or loose connections. Next, use a multimeter to check the sensor resistance. Compare the reading to the manufacturer's specifications. Test the sensor circuit for voltage and ground. Perform a continuity test on the wiring to ensure there are no breaks in the circuit. Inspect the connectors for corrosion or damage. Use a scan tool to monitor the sensor readings while the engine is running. Check the refrigerant level and perform an A/C system pressure test.

Sensor Function: The A/C high side temperature sensor functions as a thermistor. A thermistor is a type of resistor whose resistance is strongly dependent on temperature. As the temperature of the refrigerant in the high-pressure side of the A/C system increases, the resistance of the thermistor decreases. The ECU monitors this change in resistance as a voltage signal. The ECU then uses this data to determine the temperature of the refrigerant and adjust the operation of the A/C system accordingly. This is crucial for protecting the compressor and ensuring optimal cooling.

Location: The A/C high side temperature sensor is typically located on the high-pressure line of the A/C system. This line is usually found near the condenser (the radiator-like component in front of the engine) or the A/C compressor itself. The exact location can vary depending on the vehicle make and model. Consulting your vehicle's service manual is the best way to pinpoint the sensor's exact location.

Wiring Diagram Basics: Understanding the wiring diagram is essential for troubleshooting a P1535 code. The A/C high side temperature sensor circuit typically consists of two or three wires. A signal wire carries the voltage signal from the sensor back to the ECU. A ground wire provides a return path for the current. Some sensors also have a 5-volt reference wire, which provides a stable voltage source from the ECU to the sensor. By tracing these wires and testing them for continuity and voltage, you can identify any breaks or shorts in the circuit.

Tools Needed: Diagnosing a P1535 code requires a few essential tools. A multimeter is needed to check the sensor resistance and test the circuit for voltage and ground. A scan tool capable of reading A/C system data is necessary to monitor the sensor readings and check for other related DTCs. A wiring diagram for your specific vehicle is crucial for understanding the sensor circuit. Basic hand tools, such as sockets, wrenches, and screwdrivers, are needed to access the sensor and wiring. A wire stripper/crimper is useful for repairing damaged wires. A test light can be used to check for voltage and ground. Finally, a refrigerant manifold gauge set is needed to check the refrigerant levels and pressures in the A/C system.

Related DTCs: Several other DTCs can be related to a P1535 code. P0530 (A/C Refrigerant Pressure Sensor Circuit Malfunction) indicates a problem with the refrigerant pressure sensor. P0532 (A/C Refrigerant Pressure Sensor Circuit Low Input) and P0533 (A/C Refrigerant Pressure Sensor Circuit High Input) indicate that the refrigerant pressure sensor is sending an out-of-range signal. P0645 (A/C Clutch Relay Control Circuit) indicates a problem with the A/C clutch relay. Any other DTC related to the A/C system or engine cooling system can also provide additional clues about the underlying problem.

Safety Precautions: Safety should always be a top priority when working on any vehicle. Always disconnect the negative battery terminal before working on the electrical system. Be extremely careful when working around the A/C system, as it contains high-pressure refrigerant. Wear safety glasses to protect your eyes from debris. If you are not comfortable working on the A/C system, it's best to take your vehicle to a qualified technician. Refrigerant can cause frostbite if it comes into contact with skin, so handle it with care.

Frequently Asked Questions:

What does the P1535 code mean? The P1535 code signifies a problem with the A/C high side temperature sensor circuit, meaning the ECU isn't receiving a valid signal from the sensor.
Can I drive with a P1535 code? While you can drive, it's not recommended as your A/C might not function, and the engine could potentially overheat in certain conditions. Prompt repair is advised.
How much does it cost to fix a P1535 code? The cost varies, but typically ranges from $100 to $300, depending on whether the sensor needs replacing or if it's a wiring issue.
Is the A/C high side temperature sensor easy to replace? The difficulty depends on the sensor's location; some are easily accessible, while others require removing other components. Consult your vehicle's repair manual.
Will a low refrigerant level cause a P1535 code? While low refrigerant doesn't directly trigger P1535, it can cause abnormal temperature readings that indirectly lead to the code in some cases.

Conclusion:

The P1535 DTC points to a fault in the A/C high side temperature sensor circuit, impacting A/C performance and potentially engine health. Thorough diagnosis, starting with visual inspection and progressing to electrical testing, is key to identifying the root cause and implementing the correct repair.