Why Your 2015 Silverado Gas Mileage is Bad (Fuel Pump Fix)

How to Fix Poor Fuel Economy

If you're noticing your 2015 Chevrolet Silverado is guzzling more gas than it should, you're not alone. This is a common frustration that can stem from several issues, but based on reports from other owners, problems within the fuel system are a primary culprit. A failing fuel pump, in particular, is a recurring theme that directly impacts engine efficiency and mileage. As one owner, mechanic_reed, lamented after a repair: "I live in the rust belt, truck has limited rust and no major repairs until today, I had to replace rusty fuel pump. At this point should I start to consider trading it in for a newer model?" This guide will walk you through the symptoms, diagnosis, and repair for fuel economy issues on your truck, using real-world data from fellow Silverado owners.

Symptoms

Poor fuel economy rarely happens in isolation. On your 2015 Silverado, it's often accompanied by other drivability issues that point toward a deeper problem. The most common companion symptom is a noticeable loss of power, especially under acceleration or when carrying a load. The engine may feel sluggish, as if it's struggling to get enough fuel, which it very well might be.

Owners also report experiencing engine shudder or shaking, particularly at idle or during low-speed acceleration. This misfire-like sensation is a classic sign of an imbalanced air/fuel mixture, which a failing fuel pump can cause by not delivering consistent pressure. In severe cases, the issue can lead to the vehicle stalling or dying, especially after the engine is warm or when coming to a stop. This isn't just an inconvenience; it's a significant safety concern.

Another symptom to watch for is unusual noises from the fuel tank area. A worn-out fuel pump motor often whines, hums, or groans loudly when you turn the key to the "ON" position before starting, or while the engine is running. This noise is a direct cry for help from a component on its last legs. While not every owner with poor mileage reports this, it's a strong diagnostic clue when present.

Most Likely Cause

Based on aggregated owner reports and discussions, the most likely cause of persistent poor fuel economy in the 2015 Silverado is a failing fuel pump. The fuel pump is the heart of your fuel delivery system, responsible for drawing gasoline from the tank and sending it at high pressure to the engine's fuel injectors. When it begins to fail, it cannot maintain the required pressure.

A weak pump leads to a "lean" condition—too much air, not enough fuel. The engine control module (ECM) tries to compensate, but performance suffers. The engine works harder to produce the same power, burning more fuel inefficiently in the process. This directly translates to fewer miles per gallon. Furthermore, as indicated by owner mechanic_reed's experience, corrosion ("rusty fuel pump") is a significant failure point, especially for trucks in regions that use road salt. The pump assembly is mounted inside the fuel tank, and exposure to moisture and corrosive elements can lead to premature failure.

How to Diagnose

Diagnosing a fuel pump issue requires a systematic approach. You'll need a few basic tools: a fuel pressure test gauge (with the correct adapter for your truck's Schrader valve on the fuel rail), a mechanic's stethoscope or long screwdriver, and a scan tool (even a basic OBD2 code reader can help).

Step 1: Check for Diagnostic Trouble Codes (DTCs). Use your scan tool to read any stored codes. While a bad fuel pump won't always trigger a specific "P0230 - Fuel Pump Primary Circuit" code, it can cause codes related to lean conditions (P0171, P0174) or random misfires (P0300). The presence of these codes alongside poor fuel economy is a strong indicator.

Step 2: Listen for Pump Operation. With the key in the "ON" position (engine off), listen near the fuel tank (under the truck, behind the rear axle). You should hear a distinct humming sound for 2-3 seconds as the pump primes the system. A loud whine, groan, or—worse—silence, points to a pump problem. Use a stethoscope to isolate the sound.

Step 3: Perform a Fuel Pressure Test. This is the definitive test. Locate the Schrader valve on the engine's fuel rail. Connect your fuel pressure gauge. With the key on (engine off), note the prime pressure. Then start the engine and check the running pressure. Refer to your owner's manual or a service guide for the exact specification (typically between 55-62 psi for the 5.3L). A reading significantly below specification, or pressure that drops rapidly after the engine is shut off, confirms a faulty fuel pump or pressure regulator.

Step 4: Rule Out Other Common Issues. While the data points to the fuel system, quickly check for obvious issues: ensure your tire pressures are correct, verify you're not carrying unnecessary weight, and confirm you're using the recommended grade of gasoline. However, if the above tests point to the pump, these are not the root cause of a major MPG drop.

Step-by-Step Fix

Replacing the fuel pump is a moderately challenging DIY job, primarily due to the need to safely drop the fuel tank. Warning: Gasoline is extremely flammable. Work in a well-ventilated area, away from sparks or open flames. Have a Class B fire extinguisher nearby.

Step 1: Relieve Fuel System Pressure. The safest method is to locate the fuel pump fuse (check your owner's manual for location) in the under-hood fuse block. Start the engine and let it run until it stalls from fuel starvation. Then crank it for an additional 3 seconds. Disconnect the negative battery cable.

Step 2: Prepare to Lower the Tank. Siphon or use a hand-operated pump to remove as much fuel as possible from the tank through the filler neck. This makes the tank much lighter and safer to handle. Disconnect the filler neck hose and vent hose from the tank. Disconnect the electrical connector for the pump module.

Step 3: Support and Lower the Tank. Using a sturdy floor jack with a broad piece of wood to cradle the tank, support its weight. Remove the bolts or straps that secure the tank to the frame. Carefully lower the jack until you have clear access to the top of the tank.

Step 4: Remove the Pump Module. Clean the area around the pump module's locking ring thoroughly to prevent contamination. Using a special fuel pump lock ring tool or a brass punch and hammer, carefully loosen and remove the locking ring. Gently lift the pump/sending unit assembly out of the tank, being careful not to damage the float arm. Note how the filter sock is oriented.

Step 5: Install the New Pump. Transfer any necessary components (like the fuel level sender) from the old module to the new one if you purchased a complete assembly, or install the new pump into the existing module if you bought just the pump. Install a new filter sock. Carefully lower the new assembly into the tank, ensuring the seal is properly seated. Reinstall and tighten the locking ring.

Step 6: Reinstall the Tank. Reverse the removal process. Raise the tank back into position, secure it with straps/bolts, and reconnect all hoses and the electrical connector. Reconnect the battery.

Step 7: Test for Leaks and Start. Turn the key to "ON" (don't start) and listen for the pump to prime for 2-3 seconds. Check all connections for leaks. If no leaks are present, start the engine. It may crank slightly longer than usual as the system builds pressure. Verify fuel pressure with your gauge if possible. As one owner shared after their repair, the immediate return of smooth power was a clear sign of success, even if it led to bigger questions about the truck's future.

Parts and Tools Needed

• Primary Part: Fuel Pump Module Assembly. For the 2015 Silverado with the 5.3L V8, a common part number is AC Delco MU-1733 or equivalent aftermarket unit (e.g., Delphi FE0114-11B1). It's often recommended to replace the entire module rather than just the pump for reliability.
• Essential Tools: Floor jack and jack stands, fuel line disconnect tools, fuel pump lock ring tool, fuel pressure test gauge, siphon pump, basic socket/wrench set, screwdrivers.
• Supplies: New fuel tank seal (often comes with pump kit), shop rags, safety glasses, Class B fire extinguisher.

Real Owner Costs

The cost to fix poor fuel economy caused by a fuel pump varies widely between DIY and professional repair.

• DIY Repair: The part cost for a quality fuel pump module assembly typically ranges from $250 to $450. With the necessary tools (which are a one-time purchase) and an afternoon of work, your total cost is confined to the part.
• Professional Repair: At a repair shop or dealership, you are paying for parts and significant labor. The job usually takes 3-4 hours. Total costs commonly range from $1,000 to $1,800, with dealerships at the higher end. This high cost is a major reason owners contemplate their next move. As owner snowforfun4 questioned when facing a major engine repair: "Would you 1.) try to sell it as is, 2) put the engine in then continue with plan to sell it? It is a work truck so I need reliability and a newer model is definitely the outcome." A four-figure repair bill forces a cost-benefit analysis on any vehicle.

Prevention

Preventing premature fuel pump failure revolves around mitigating its two biggest enemies: heat and contamination.

1. Keep Fuel in the Tank: Never consistently run your truck on "E." The fuel pump is submerged in gasoline, which cools it during operation. Driving regularly with a very low fuel level allows the pump to overheat, shortening its lifespan. Try to keep the tank above a quarter full.
2. Use Quality Fuel: Purchase gasoline from reputable, high-volume stations. This reduces the risk of filling up with contaminated fuel or fuel containing excessive moisture, which can damage the pump.
3. Address Rust Proactively: For trucks in the rust belt, regular undercarriage washes in the winter to remove salt are crucial. While it won't protect the sealed inside of the tank, it fights the external corrosion that can attack tank seams, straps, and lines. Owner ShillinTheVillain noted about rust: "It can be salvaged if you want to grind and recoat but I'd probably pass on that. It's indicative of other routine maintenance being neglected." Proactive care is key.
4. Change Your Fuel Filter: While the 2015 Silverado has a "lifetime" filter sock on the pump, if you experience any symptoms of contamination (sputtering, loss of power), addressing it immediately can protect the pump.

What Owners Say

Real experiences from CHEVROLET owners:

Owner Experiences

"I live in the rust belt, truck has limited rust and no major repairs until today, I had to replace rusty fuel pump. At this point should I start to consider trading it in for a newer model?" — mechanic_reed (source)

"At this point should I start to consider trading it in for a newer model? I really like my truck." — mechanic_reed (source)

"Are you telling me the newer models are lasting less than that? I'm glad I traded in my 2015 Sierra for a 2006 Silverado." — Cleanbadroom (source)

Real Repair Costs

"Just put a $7k transmission in my 2015 Silverado @ 142k miles. Google "Silverado transmission shudder"." — bluefoxTNT (source)

FAQ

Q: How long does it take to replace a fuel pump on a 2015 Silverado? A: For a seasoned DIYer with all tools and parts ready, plan for 3 to 5 hours, largely dependent on how much fuel is in the tank and dealing with any rusty fasteners. A professional mechanic in a shop typically bills 3-4 hours of labor.

Q: Can I drive my Silverado with a failing fuel pump? A: It is not recommended. A failing pump can cause sudden stalling, loss of power while driving (especially when needing acceleration to merge or climb a hill), and can leave you stranded. It is a safety risk and should be addressed promptly.

Q: Is poor fuel economy a common issue on the 2015 Silverado? A: Based on owner discussion data, fuel system issues, including pump failures that lead to poor MPG, are a commonly reported problem as these trucks age and accumulate mileage, particularly in corrosive environments.

Q: DIY vs mechanic – what's recommended for this repair? A: This is a high-intermediate DIY job. If you are mechanically inclined, have a safe workspace, and proper tools (especially a way to safely support and lower a fuel tank), you can save $600-$1,300. If you are uncomfortable working with fuel systems, lack the tools, or your truck is severely rusted, the investment in a professional is wise for safety and certainty. The high shop cost does lead some owners to consider their options, as reflected in the community.

Q: Could using thicker oil improve my fuel economy? A: Some owners anecdotally report subjective improvements in engine smoothness after switching, like Responsible-Plan-631 who said: "Switch to 5w30 at 100k miles on my 2015 Silverado Lt 5.3 . Much better than that water down 0w20." However, for a measurable fuel economy problem caused by a faulty component like a fuel pump, changing oil viscosity is not a fix. It may slightly reduce internal engine friction in a worn engine but will not compensate for a failed fuel delivery system.

Q: After fixing the fuel pump, will my MPG return to normal immediately? A: You should notice an immediate improvement in power and drivability. However, for the engine computer to fully re-adapt its long-term fuel trims and for you to calculate an accurate MPG average, it may take a few full tanks of fuel and some normal driving cycles to see the stabilized, optimal fuel economy.