2018 GMC Sierra Fuel Pump & EVAP Leak Repair: A Detailed Walkthrough

Diagnosing the Issue

• 💡 The 2018 GMC Sierra presented with a fuel tank pressure sensor performance code and an EVAP leak.
• 🎯 The EVAP leak was traced to the top of the fuel pump assembly, specifically a rust-swollen lock ring that cracked the fuel sending unit.

Fuel Tank Removal and Preparation

• 🛠️ The repair requires dropping the fuel tank, ideally when it's nearly empty to minimize weight and spillage.
• ⚙️ The process involves unhooking the drive shaft, transmission jack support for the fuel tank, and disconnecting the filler neck and fuel/EVAP lines.
• ⚠️ Care must be taken when unhooking lines due to residual fuel pressure, which can result in a small spray.

Fuel Pump Assembly Replacement

• 🔑 The original fuel pump assembly was removed by turning a lock ring, which was surprisingly easy to loosen.
• 🧩 The cracked fuel sending unit, caused by the swelling metal lock ring, was the source of the EVAP leak.
• 🔩 A new fuel pump assembly from Chevrolet was installed, ensuring correct orientation and secure connection of all lines.
• 🔨 The new lock ring was installed using a plastic hammer handle and then a brass hammer to avoid sparks, ensuring a secure fit.

Reassembly and Testing

• 🚀 After reassembly, the drive shaft, filler neck, and fuel lines were reconnected, and the tank straps were secured.
• 💨 A Crown penetrating oil was applied to fight rust on the tank straps and surrounding areas.
• 🚗 The vehicle was started, and after a couple of key cycles, the check engine light remained off, indicating the repair was successful.

Post-Repair Diagnostics

• 🔍 A full system scan was performed, clearing self-induced codes related to the repair process.
• 📊 Data was reviewed to confirm the fuel tank pressure sensor was functioning correctly, reading approximately 1.5-1.6 volts and showing proper sealing and venting behavior during EVAP system tests.
• ✅ The fuel gauge was observed to be slightly below a quarter tank, and TPMS codes were noted but deemed unrelated to the primary repair.