B1861

Code

LAND ROVER B — Body

Climate control pressure switch - short circuit to ground

Brand: LAND ROVER

Type: B — Body

Views: UK: 15 EN: 27 RU: 16

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Page language: EN

Causes

Damaged or pinched wiring harness in pressure switch circuit
Corroded, bent or pushed-out connector pins at the pressure switch
Pressure switch internal short (failed switch)
Aftermarket equipment or recent repairs that disturbed the harness
Control module input shorted to ground or module fault

Symptoms

A/C compressor may not engage or cycles incorrectly
Reduced or no air conditioning performance
HVAC warning or fault lamp stored in instrument cluster
Diagnostic trouble code B1861 stored in memory
Intermittent A/C operation if wiring movement causes intermittent short

What to check

Read and record all stored codes and freeze frame data; note any related HVAC or BCM codes
Visually inspect the pressure switch connector and wiring harness for damage, corrosion, or water
Backprobe pressure switch signal with ignition ON and compare to expected reference voltage
Measure continuity between signal wire and chassis ground (with harness disconnected) to confirm short
Disconnect the switch and check whether the code clears or changes (to isolate wiring vs switch)
Consult wiring diagram to identify related fuses, relays and connector pinouts before testing

Signal parameters

Typical pressure switch operation: open/closed contact providing either near 0 V (ground) when closed or pulled up to a reference voltage when open
Expected voltage at signal connector with switch connected and system OFF: approx. reference voltage (typically ~5 V) or vehicle-specific pull-up
Expected voltage at signal connector with switch actuated (low pressure or high pressure depending on design): approx. 0 V (ground) if switch closes to ground
Continuity: normal open when switch open; continuity to ground only when switch closed
Resistance: short to ground will show very low ohms (

Diagnostic algorithm

Retrieve codes and freeze frame. Note any related chassis or HVAC codes.
Perform a visual inspection of the A/C pressure switch connector and nearby wiring for chafing, moisture, corrosion, bent pins or recent repair splices.
With ignition ON (engine off), backprobe the pressure switch signal wire at the connector. Record the voltage with the switch connected and then with it disconnected. Refer to vehicle-specific service data for exact reference voltages.
With harness disconnected, measure continuity between the signal wire and chassis ground. A short is indicated by very low resistance. If present, trace the harness and repair insulation or replace damaged section.
If no short to chassis is found, test the pressure switch by measuring its resistance or by substituting a known-good switch per service procedure. Replace the switch if it fails.
If the switch and harness check good, inspect/replace or test the control module input circuit: check for shorts, proper pull-up voltage at module connector, and proper fusing/relays. Use wiring diagrams to isolate the circuit.
After repairs, clear codes and perform a road or functional test to confirm the fault does not return. Re-scan for codes.

Likely causes

Chafed insulation where the harness rubs against chassis or engine components, contacting ground
Water intrusion/corrosion in the pressure switch connector causing low resistance to ground
Failed pressure switch with internal shorting
Poor repair splices or connectors tied to ground
Faulty HVAC/BCM input stage (less common)

Fault status

⚠️ Status

Climate control pressure switch circuit short to ground — the control module detects the pressure switch signal permanently grounded. Inspect switch, connector and wiring for shorts or corrosion.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 2.0 hours

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