4D4785 (4D-4785) Caterpillar Low Oil Pressure Switch, with a trigger pressure of 4 psi (≈27.6 kPa), used for low-pressure alarm protection in older CAT engines and heavy machinery. I. Core Specifications (OEM Standard)

Table

Parameter Item | Detailed Specification

Part Type | Mechanical Oil Pressure Switch (Normally Closed Type)

Trigger Pressure | 4 psi (27.6 kPa) — Alarm Activated (Closed)

Reset Pressure | Approx. 2–3 psi (13.8–20.7 kPa)

Contact Type | Normally Closed (NC): Conducts (activates alarm) when pressure drops below 4 psi

Electrical Interface | Single Screw Terminal / 2-Pin Simple Connector

Mounting Thread | 1/8"-27 NPT (American Taper Pipe Thread)

Rated Current | 10–15A (Universal for 12V/24V systems)

Operating Temperature | -40°C to 125°C

Protection Rating | IP54 (Dust-proof and Splash-proof)

Weight | Approx. 0.09 kg (0.20 lbs)

II. Applicable Models (Classic/Older Series)

Engines: 3304, 3304B, 3306, 3306B

Motor Graders: 120G, 12F, 12G, 130G, 140G, 14E, 14G, 16, 16G

Excavators: 215, 215B, 215C, 215D, 225, 225D, 229, 229D, 235, 245

Loaders: 518, 518C, 528, 561C

Scrapers: 621, 621B, 627, 627B, 637, 637B

Dozers: D5, D6C, D7F, D7G, D8H

III. Replacements and Interchangeability

Direct OEM Interchange: CA4D4785

V. Fault Diagnosis and Self-Check

Alarm Light Stays On: Oil pressure is normal, yet alarm persists → Internal switch contacts are stuck (welded) / Short circuit

Alarm Light Does Not Turn On: Oil pressure is too low, yet no alarm sounds → Switch Contacts Open / Failed

Self-Diagnostic Procedure:

Disconnect the plug and use a multimeter to measure across the switch terminals: Continuity should be present at pressures <4 psi, and the circuit should be open at pressures >4 psi.

Check the terminals for oxidation or looseness, and inspect the wiring harness for damage.