238-4676 (1GP4004) — Caterpillar Crankshaft Speed / Position Sensor (Magnetic Pickup Type). Designed for Caterpillar medium excavators and wheeled excavators, it provides engine speed and crankshaft position signals. I. Core Parameters and Specifications

OE Model: 238-4676 (Caterpillar Original; also written as 2384676); 1GP4004 is an equivalent / replacement part number.

Type: Magnetic Pick-up (VR) Crankshaft Speed / Position Sensor

Function: Detects crankshaft speed and position, providing injection / ignition timing signals to the ECM.

Electrical Interface: 2-pin waterproof connector (passive—requires no external power supply; outputs AC pulse signals).

Thread Specification: M16×1.5 (Metric Fine Thread)

Installation Gap: 0.8–1.2 mm (clearance between the sensor tip and the signal wheel teeth).

Output Signal: AC voltage pulses (voltage increases with engine speed).

Compatible System: Caterpillar Medium-Duty Electronic Fuel Injection (EFI) Engine Control Systems.

II. Compatible Models (Frequently Applicable)

Excavators: 317D, 322D, 323D, M313C, M315D, M316F, M317, MH302, and other wheeled / small-to-medium hydraulic excavators.

Engines: C4.2, C6.4, C7, and other medium-duty electronic fuel injection engines.

Others: Select Caterpillar wheel loaders and motor graders utilizing the same platform/components.

III. Replacement Models and Suppliers

Table

Type | Replacement Model | Description

Original Equivalent | 1GP4004 | Caterpillar internal part number; fully interchangeable with 238-4676.

V. Fault Symptoms and Troubleshooting

Common Faults:

Engine fails to start or is difficult to start.

Unstable idle speed, poor acceleration, or jerky operation while driving.

Diagnostic Trouble Codes (DTCs): P0335 (Crankshaft Position Sensor Circuit Malfunction), P0336 (Crankshaft Position Sensor Signal Implausible).

Troubleshooting Steps:

Check the 2-pin connector for looseness, corrosion/oxidation, or water ingress.

Measure sensor resistance: Should be 800–1500Ω (at room temperature); if resistance is infinite (open circuit) or 0Ω (short circuit), the sensor is defective.

Measure the AC signal output: During engine cranking, a pulse voltage of at least 0.5V should be present; if no signal is detected, replace the sensor. Check the installation gap: Ensure it is between 0.8 and 1.2 mm. A gap that is either too large or too small will result in no signal.

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