122-8863 (1228863) Caterpillar Low-Output Magnetic Speed Sensor—primarily used to monitor the rotational speed of the engine crankshaft, flywheel, or transmission, and to provide speed signals to the ECU. I. Core Basic Information

Part Number: 122-8863 (1228863)

Type: Magnetic Pickup Speed Sensor (Passive / Low Output)

Brand: Caterpillar

Function: Detects the rotational speed of moving components and outputs a pulse signal to the ECU; used for engine timing, idle speed control, transmission shifting, and overspeed protection.

II. Key Technical Specifications

Electrical: 2-Pin Connector (CAT Standard); Passive Magnetic Induction (requires no external power supply)

Thread Specification: 3/4"-16 UNF (External Thread)

Thread Length: 1.35 inches (approx. 34.3 mm)

Operating Temperature: -40°C to +125°C

Material: Metal housing, sealed probe; resistant to vibration and oil/contaminants

System Compatibility: Universal for 12V/24V Electronic Control Systems

III. Primary Compatible Engines

3126, 3176C, 3406, 3412E

C7, C9, C27, C32, and other large electronically controlled engines

IV. Primary Compatible Equipment

Excavators

312B, 320B, 330B, 345B

Loaders / Wheel Dozers

938G, 950G, 962G, 990K, 992K, 993K, 844K, 854K

Dozers

D6R, D6T, D7R, D10R

Motor Graders

12H, 120H, 140H, 143H, 163H, 24H

Articulated / Off-Highway Trucks

725, 730, 735, 772G, 773E/F/G, 775E/F/G, 777E/F/G

V. Alternative Models 122-8864 (Same series; high-output version)

189-5769, 245-4630, 318-8856 (Common OEM replacement part numbers)

VII. Common Faults and Replacement Guidelines

Fault Symptoms

Engine fails to start or is difficult to start

Tachometer displays no reading or fluctuates erratically; ECU reports a speed sensor fault (e.g., P0335, P0336)

Unstable idle speed, insufficient power, or abnormal transmission shifting

Replacement Guidelines

Install onto the flywheel housing or transmission housing, ensuring proper alignment with the signal gear ring

Clean the mounting bore to ensure the clearance between the sensor probe and the gear ring is within the normal range (0.8–1.5 mm)

Tighten to the specified torque (approximately 40–50 N·m)

Perform a test run after installation to verify the tachometer display and engine operating status