398-0940 (3980940) Caterpillar (CAT) 24V Intake Air Heater Relay / Solenoid Switch, specifically designed for C7, C9, C11, C13, C15, C18, and similar series of electronically controlled engines, controlling the high-current circuit for the intake air heater plugs. Image

I. Core Specifications

Part Number: 398-0940 / 3980940

Official Name: Magnetic Switch / Air Inlet Heater Relay

Coil Voltage: 24V DC

Contact Capacity: 100A (High-current capacity, specifically for glow plugs)

Structure: 2 Main Terminals + 1 Plug with Lead Wires (2-wire)

Type: Normally Open (NO); Energizes to Engage

Mounting: Metal Bracket, 2-Hole Fixing

II. Compatible Engines and Machine Models

Caterpillar Engines

C7, C9, 3126B

C10, C11, C13, C15, C18, C27, C32

Applicable Equipment

Excavators: 320D, 324D, 325C/D, 330C/D, 336D, 345D

Wheel Loaders: 950H, 962H, 966H, 972H, 980H

Dozers: D6N, D6R, D7R, D8T

Off-Highway Trucks / Generator Sets: 769D, 773E, 3456, C15/C18 Generator Sets

III. Replacement / Cross-Reference Models

209-5582 (2095582) (Fully Interchangeable)

223-4453 (Same Function; Different Wiring Harness)

144-9955 (Earlier Model)

VI. Common Faults and Diagnostics

Fault Symptoms: Difficulty starting when cold, pre-heat indicator light fails to illuminate, no response during pre-heating, contact pitting/burnout.

Diagnostics

Coil Resistance: Approx. 40–60Ω at 24V

Direct 24V Power Supply Test: Should audibly click (engage) and main contacts should show continuity.

Inspection: Check plug and terminals for oxidation, looseness, or scorching/blackening.