GM GENUINE PARTS DEF Tank Filler Cap 23138955 — OEM Fit, Durable Seal for GM Diesel Vehicles

GM Genuine Parts 23138955 is the original-equipment diesel emissions fluid (DEF) tank filler cap engineered to fit GM diesel vehicles and maintain the DEF system seal.

This DEF tank filler cap is a factory-validated replacement from GM Genuine Parts, made to the same specifications used during vehicle production. It restores a proper seal on the DEF reservoir, helps protect the fluid from contaminants and evaporation, and ensures the cap interfaces correctly with the vehicle’s fill neck and onboard sensors. The part is designed, tested, and supported by General Motors and may have been previously listed under ACDelco GM Original Equipment (OE).

How does this cap preserve my DEF system?

The GM Genuine Parts filler cap provides a precise fit that prevents moisture, dirt, and debris from entering the DEF tank while minimizing fluid loss from evaporation. A correct seal helps the vehicle’s dosing and exhaust aftertreatment systems perform as intended without false sensor readings caused by a loose or damaged cap.

• OE-matched dimensions for secure sealing against the fill neck
• Durable materials resist chemical exposure from DEF
• Proper fit reduces risk of contamination and sensor errors

Will this cap fit my GM truck or SUV?

Part number 23138955 is manufactured to GM’s original specifications and is intended for compatible GM diesel models. Always verify part compatibility using your vehicle’s VIN or consult a GM dealer or parts catalog to confirm fitment before purchase.

• Designed and validated by GM engineers for GM vehicles
• Cross-reference with your vehicle’s parts list or VIN
• May replace previously marketed ACDelco GM OE parts

What are the practical benefits of using an OEM DEF cap?

Choosing an OEM GM cap ensures consistent fit and function with factory components and reduces the chance of leaks or sensor-related warnings caused by aftermarket mismatches. OEM parts also follow GM’s materials and testing standards so they resist DEF exposure and temperature changes better over time.

• Reliable sealing to prevent fluid contamination
• Compatibility with onboard monitoring and diagnostics
• Backed by General Motors’ engineering and validation

Are there any safety or regulatory notes I should know?

DEF is a urea-based solution and should be stored and handled per manufacturer guidance. This GM Genuine Parts cap is a passive component; follow vehicle and DEF container warnings for safe handling. Note: product listings may carry regulatory notices—some states require consumer warnings about chemical exposures.

• Handle DEF with gloves if skin contact is a concern
• Avoid mixing contaminants into the DEF reservoir
• Check local regulations and product labeling for specific warnings

Who is this for: This part is intended for owners, fleet managers, and technicians who maintain GM diesel vehicles and need a direct OE replacement for a worn, lost, or damaged DEF tank filler cap. It’s the right choice when you want an exact, factory-style fit to protect the DEF system and maintain vehicle reliability without custom modifications.