OBD-II Fault Code

B1859: Climate Control A/C Pressure Switch Circuit Open

Meaning, symptoms, likely causes, diagnostic checks and repair guidance for B1859.

System family

Body

Manufacturer-specific

Repair category

HVAC / climate control

Use this category to narrow your checks before replacing parts.

Severity

Low

Severity is a general guide. Confirm with scan-tool data and vehicle symptoms.

What B1859 usually means

Climate Control A/C Pressure Switch Circuit Open.

Common symptoms

Body/accessory warning lamp or feature not working

Likely causes

Faulty control head/switch; Blend door actuator fault; Blower resistor/motor issue; Wiring/fuse fault; Open circuit; Disconnected connector; Broken wire; Failed component

Diagnostic checks

Check related fuses, connectors, grounds and switch/module power supply; Check HVAC fuses, actuator movement and scan-tool HVAC data if available; Check connector fitment and continuity from module to component

Repair guidance

Repair wiring/fuse issue, replace failed actuator/motor/control part after testing; Repair open wire/connector or replace the failed component after continuity test

Verification after repair

Operate the affected body/accessory system and rescan

Note: Confirm vehicle make/model/year because manufacturer-specific codes can vary; Manufacturer-specific: confirm definition and test steps in the vehicle service manual. A DTC identifies a circuit or system condition, not always the failed part.