238-4676 (1GP4004) Magnetic Crankshaft Speed / Position Sensor (Sensor GP-Speed)—designed for Caterpillar C6.6, C7.1, and similar engines—provides crankshaft position and speed signals to control fuel injection timing and starting logic.

I. Key Specifications

Part Number: 238-4676 (2384676); Associated Number: 1GP4004

Type: Magnetic Inductive (Passive) (Non-Hall Effect)

Function: Monitors crankshaft speed and position; outputs an AC sine wave signal to the ECM.

Electrical: 2-pin waterproof connector; Passive signal (requires no external power supply); Output AC voltage increases as engine speed rises.

Mechanical: Threaded mount; IP67 protection rating; Operating temperature: -40°C to 125°C.

Replacement For: 191-8308, 247-5295 (Directly interchangeable).

II. Compatible Models

Engines: C6.6, C7.1, C4.4 ACERT

Excavators: 317D, 322D, 323D, 324D, 325D, 329D, 330D

Loaders: 924K, 930K, 938M, 950GC

Others: Motor Graders 12M, 140M; Generator Sets XQ230, CG137

III. Fault Symptoms and Diagnostics

Symptoms: Hard starting / Failure to start, Unstable idle, Poor acceleration, Tachometer anomalies, Engine stalling.

Diagnostic Codes: P0335 (Crankshaft Sensor Circuit), P0336 (Signal Anomaly).

Testing Procedures:

Measure sensor coil resistance (approx. 800–1200 Ω).

Measure output AC voltage during cranking (should increase as engine speed rises).

Check mounting air gap (0.8–1.5 mm) and inspect connector for corrosion.