B1859 – Climate Control A/C Pressure Switch Circuit Open

The ODBII code B1859 indicates that there is an open circuit in the A/C pressure switch, which can prevent the climate control system from functioning properly.

The severity of ODBII code B1859 is moderate.

Common Causes For: B1858 Climate Control A/C Pressure Switch Circuit Failure

• Faulty A/C pressure switch
• Open or damaged wiring in the circuit
• Poor electrical connections
• Blown fuse
• Malfunctioning A/C control module
• Refrigerant leaks or low refrigerant levels

Common misdiagnosis for B1859 Climate Control A/C Pressure Switch Circuit Open

• Faulty A/C compressor
• Refrigerant leak
• Bad A/C pressure switch
• Wiring issues or shorts in the circuit
• Faulty climate control module
• Incorrect refrigerant charge
• Malfunctioning blower motor
• Faulty relay or fuse related to A/C system

Common Troubleshooting Steps

The OBD-II code B1859 indicates a problem with the climate control system, specifically related to the A/C pressure switch circuit being open. Here are some common troubleshooting steps to diagnose and resolve this issue:

• Check the A/C Pressure Switch:
• Inspect the A/C pressure switch for any visible damage or corrosion.
• Use a multimeter to test the switch for continuity. If the switch is open when it should be closed (or vice versa), it may need to be replaced.
• Inspect Wiring and Connectors:
• Examine the wiring harness and connectors leading to the A/C pressure switch for any signs of damage, fraying, or corrosion.
• Ensure that all connections are secure and free of dirt or moisture.
• Check A/C System Refrigerant Level:
• Low refrigerant levels can cause the A/C pressure switch to open. Check the refrigerant level and recharge the system if necessary.
• Look for any signs of refrigerant leaks in the system.
• Test the A/C Pressure Sensor:
• If applicable, test the A/C pressure sensor (if separate from the switch) to ensure it is functioning correctly.
• Use a scan tool to monitor the pressure readings while the A/C is running.
• Inspect the A/C Control Module:
• Check for any fault codes in the A/C control module using a scan tool. There may be additional codes that can provide more context for the issue.
• If the control module is faulty, it may need to be reprogrammed or replaced.
• Check for Ground Issues:
• Ensure that the ground connections for the A/C system are secure and free of corrosion. A poor ground can lead to circuit issues.
• Look for Other Related Codes:
• Check for any other OBD-II codes that may be related to the climate control system. Addressing these codes may resolve the B1859 code.
• Perform a Visual Inspection:
• Conduct a thorough visual inspection of the entire A/C system, including the compressor, condenser, and evaporator, for any signs of damage or leaks.
• Clear Codes and Test Drive:
• After performing repairs or replacements, clear the trouble codes using a scan tool and take the vehicle for a test drive to see if the code returns.
• Consult Service Manual:
• Refer to the vehicle’s service manual for specific diagnostic procedures and specifications related to the A/C system and the B1859 code. If the issue persists after following these steps, it may be advisable to consult a professional mechanic or technician for further diagnosis and repair.