A/C Pressure Switch Circuit High Voltage
The B1860 code indicates that the Body Control Module (BCM) or HVAC control module has detected an excessively high voltage (short to battery/positive) in the A/C pressure switch signal circuit. This switch protects the compressor by disabling it if refrigerant pressure is too high or low; a short to positive prevents correct pressure reading, disabling the climate control system as a safety measure.
1. Commonly Affected Makes
2. Most Common Causes
- Signal wire shorted to 12V (damaged insulation, chafing)
- Faulty A/C pressure switch with internal short to power
- Damaged internal pull-up driver in HVAC/BCM module
- Corroded or bent pins in pressure switch connector contacting power terminal
3. Symptoms You Will Notice
- A/C system inoperative or blows warm air
- Compressor clutch does not engage
4. Step-by-Step Diagnosis
Check for technical service bulletins (TSBs) related to B1860
Visually inspect A/C pressure switch connector for corrosion, damage, or bent pins
Measure voltage at pressure switch signal wire with ignition on; should be near 0V when disconnected, not 12V
If voltage is 12V, disconnect switch; if voltage drops to 0V, replace switch; if remains 12V, repair short to power in wiring or check HVAC/BCM module
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, but the A/C will not work. Driving without A/C is safe, though in hot weather it may be uncomfortable.
How much does it cost to fix?▼
Typically $100–$300, depending on whether it's a wiring repair ($50–$150) or switch replacement ($80–$200).