B1861

Code

Other B — Body

Climate Control A/C Pressure Switch Circuit Short To Ground

Brand: Other

Type: B — Body

Views: UK: 24 EN: 41 RU: 27

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Page language: EN

Causes

Damaged/abraded wiring harness with conductor contacting chassis ground
Corroded, bent or pushed-out terminal in pressure switch connector
Faulty A/C pressure switch internally shorted to ground
Water intrusion or contaminant in connector creating unintended ground
Improper aftermarket component or incorrect replacement switch
Faulty body or HVAC control module (less common)

Symptoms

A/C compressor will not engage or engages intermittently
Reduced or no cooling from HVAC system
DTC B1861 stored; possible warning/lamp on climate control display
Blown A/C fuse or repeated fuse failures in some cases
Intermittent A/C operation or limp mode of climate system

What to check

Retrieve freeze frame and related codes to confirm conditions when code set
Inspect wiring harness from the pressure switch to the HVAC/body control module for abrasion, pinches or impact damage
Visually inspect the pressure switch connector for corrosion, bent pins, pushed-out terminals or moisture
Check nearby grounding points and chassis for signs of chafing where the harness is routed
Verify fuses and relays in the A/C/climate circuits are intact
Consult vehicle wiring diagram to identify wire colors, pin locations, and whether the switch is switched-to-ground or switched-to-supply

Signal parameters

Expected: pressure switch typically is a switched circuit — closed or low resistance when pressure within range; open/high resistance when out of range (specs vary by vehicle)
Typical reference voltages: 0–0.5 V (circuit pulled to ground) indicates a hard short to ground; ~5 V or battery voltage on the switch signal may indicate open circuit or pull-up (vehicle-dependent)
Resistance: near 0 Ω across switch when closed; very high (kΩ to open) when open — confirm with manufacturer spec
Continuity to chassis ground on the signal wire should be very low if a short to ground is present (near 0 Ω); otherwise should be open/infinite

Diagnostic algorithm

Record current codes and freeze frame data; note engine on/off and A/C requests when fault occurred.
Visually inspect the pressure switch and connector for damage, corrosion, moisture, or evidence of recent repairs.
Disconnect the pressure switch; inspect terminals and connector housing. Look for pushed-out pins or pinched wires.
With the switch disconnected, measure resistance between the signal wire and chassis ground. If near 0 Ω — wiring is shorted to ground; trace and repair harness.
Backprobe the pressure switch connector with ignition ON (engine OFF). Measure voltage on the signal pin relative to ground. A steady 0 V on the signal with disconnected switch indicates a short to ground in the wiring or module.
If the signal wire isn’t shorted with the switch disconnected, check the switch itself: measure continuity across the switch body terminals while applying expected pressure conditions (or compare to known-good switch). Replace if internally shorted.
Wiggle harness along its routing while monitoring the signal for intermittent changes to find an intermittent short.
If harness and switch check OK, inspect/bench-test HVAC/body control module outputs and grounds. Check for internal short in module by substituting a known-good module if available or follow manufacturer module bench test procedures.
Repair any damaged wiring: isolate and replace sections, repair connectors, apply proper sealing, and secure harness away from chafing points. Replace faulty pressure switch if required.
Clear codes and verify repairs with functional test: start vehicle, cycle A/C on, monitor live data for pressure switch signal and confirm compressor operation under normal conditions.

Likely causes

Chafed wire contacting body or engine block near routing path
Connector pin pushed through housing and touching mating shell or retained clip
Pressure switch failed electrically and is grounding the signal circuit
Connector corrosion after road-salt or water exposure causing low resistance to ground