I. Core Parameters and Specifications

Original Part Numbers: 320-04378, 320/04378, 32004378

Type: Mechanical Pressure Switch (Alarm Type); Non-Analog Sensor

Core Function: Monitors engine oil pressure; triggers the dashboard warning light when pressure drops below the threshold.

Electrical Characteristics: Single-pin / Single-contact; contact closes (grounds the circuit to trigger an alarm) when pressure falls below the threshold.

Mechanical Parameters:

Thread: 1/8 NPT or M12×1.5 (JCB Standard Interface)

Operating Temperature: -40°C to 125°C

Protection Rating: IP67

Pressure Threshold: 0.3–0.6 bar (Low-pressure alarm; triggers when pressure falls below this range).

Compatible Systems: 12V/24V Heavy Equipment Electrical Systems

II. Compatible Models (Primarily JCB)

Backhoe Loaders: 3CX, 4CX (Full Series)

Excavators: JS200, JS220, JS240

Others: JCB Wheel Loaders, Telehandlers (Select Models)

III. Fault Symptoms and Diagnostics

Typical Symptoms:

Oil pressure warning light remains illuminated after engine startup (even when pressure is normal).

No alarm triggers when pressure is critically low (indicating an open circuit at the contact).

Alarm triggers at idle or low engine speeds, but clears at high speeds (indicating switch aging or poor contact).

Quick Diagnostics:

Disconnect the sensor connector and short-circuit the pins within the connector: If the warning light turns off, the switch has an internal open circuit.

Start the engine and measure the resistance between the switch terminal and ground: The circuit should be open (∞Ω) when pressure is normal, and closed (0Ω) when pressure falls below the threshold.

Verification via Mechanical Pressure Gauge: Remove the switch, install a mechanical pressure gauge, and verify whether the alarm pressure corresponds to the 0.3–0.6 bar range.

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