The 2004 Chevrolet Impala Fuel Pump: Failure Signs, Replacement Guide & Costs

Owning a reliable 2004 Chevrolet Impala? Recognize and resolve fuel pump problems promptly. This critical component, submerged inside the fuel tank, delivers pressurized gasoline to your engine. A failing fuel pump in your 2004 Impala manifests through distinct symptoms like engine stalling, loss of power, hard starting, or the vehicle failing to start altogether. Ignoring these signs risks leaving you stranded. Replacement involves lowering the fuel tank, requires careful safety procedures, and typically costs between $450and$850 for professional service depending on parts choice and labor rates. With the right tools and precautions, a determined DIYer can undertake this repair, potentially saving on labor costs.

Recognizing Symptoms of a Failing Fuel Pump (2004 Impala)

The fuel pump is the heart of your Impala's fuel delivery system. When it starts to weaken or fail, your car sends clear signals demanding attention. Being able to accurately identify these symptoms is the first critical step towards addressing the problem and restoring reliable operation. Don't dismiss these warning signs; prompt action can prevent costly breakdowns or unsafe situations.

• Engine Cranks But Won't Start (No Start): This is arguably the most direct and alarming symptom. If you turn the key and the engine cranks strongly (you hear the starter motor turning the engine) but it never actually catches and runs, the fuel pump is a prime suspect. A completely failed pump means no fuel pressure reaches the engine cylinders, making combustion impossible. Important Note: While a no-start can be caused by other issues like ignition failure or a dead battery (which usually causes no cranking), a crank-no-start strongly points towards fuel delivery or spark issues.
• Vehicle Loses Power, Stalls, or Sputters While Driving: A weakening pump struggles to maintain consistent fuel pressure, especially under higher engine loads or demand. You might experience:
  • Sudden loss of power: The car feels like it's being starved of fuel during acceleration or even while cruising.
  • Unexpected stalling: The engine dies suddenly, often at low speeds like approaching a stop sign or traffic light.
  • Hesitation and sputtering: The engine coughs, bucks, or lacks responsiveness when you press the gas pedal. This often happens when trying to accelerate, merge onto a highway, or climb a hill.
• Engine Starts Then Immediately Dies: You might successfully start the engine, only for it to stall seconds later (often within 1-5 seconds). This behavior frequently indicates a fuel pump relay problem (which can sometimes reset briefly), but it also strongly suggests a fuel pump that has failed and can't maintain pressure once the initial priming cycle stops. If the relay has been ruled out, the pump itself is likely the culprit.
• Difficulty Starting / Extended Cranking: Before failing completely, a weakening pump often makes starting the engine take noticeably longer. Instead of starting immediately, you might need to hold the key in the "start" position for several seconds before the engine finally catches and runs. This happens because the pump takes longer to build the necessary fuel pressure in the rail for proper combustion.
• Reduced Engine Performance and Fuel Economy: Less severe than sputtering or stalling, a pump on its last legs might cause a noticeable decrease in engine responsiveness and overall power, particularly noticeable during quick acceleration. You might also observe a subtle drop in miles per gallon (MPG), as the engine control unit (ECU) tries to compensate for inconsistent fuel flow by adjusting the air-fuel mixture, often making it richer (using more fuel).
• Whining Noise from the Fuel Tank Area: While some fuel pump noise is normal for a few seconds when you first turn the key to "on" (before starting), a distinctly loud, high-pitched whining, humming, or droning sound that persists while driving, especially under load, signals a pump under significant stress or wearing out. This noise often becomes louder or more noticeable as the pump struggles, like when the fuel level is low. Change in the normal sound when priming is also a warning sign.
• Check Engine Light (CEL) with Related Codes: While a faulty fuel pump itself doesn't always trigger a direct code, the resulting conditions – insufficient fuel pressure or rail pressure, lean running conditions caused by lack of fuel – can illuminate the Check Engine Light. Common codes that might accompany a failing fuel pump include:
  • P0171/P0174: System Too Lean (Bank 1/Bank 2) - Indicates too much air relative to fuel.
  • P0230: Fuel Pump Primary Circuit Malfunction - Points to an electrical problem controlling the pump (relay, fuse, wiring). While not directly the pump, this circuit powers it.
  • P0190-P0194: Fuel Rail Pressure Sensor Circuit Malfunctions - Sensor issues can mimic pump problems, but low sensor readings might be caused by the bad pump.
  • P0087: Fuel Rail/System Pressure Too Low - A direct indication of insufficient fuel pressure reaching the engine.
  • Importantly, these codes only indicate the symptom (low pressure, lean condition, circuit fault). Further diagnosis is crucial to pinpoint the root cause as the fuel pump, relay, wiring, filter, or sensor.

Why Do 2004 Impala Fuel Pumps Fail? Common Causes

Understanding why your 2004 Impala's fuel pump might fail helps with prevention and diagnosis. While not immune to random component failure, several common factors contribute significantly to shortening the life of this crucial part.

• Electrical Component Wear & Overheating: Inside the submerged pump assembly is an electric motor. Like any motor, its windings, brushes (in some designs), or internal connections can degrade over time due to constant use and heat generated during operation. Running the vehicle consistently on a very low fuel level increases this overheating risk, as the fuel surrounding the pump motor acts as a coolant. A burned-out pump motor is a common failure mode.
• Fuel Contamination Issues: The fuel pump relies on gasoline not just for power, but also to lubricate its moving parts. Contaminants entering the tank are a major threat:
  • Dirt and Debris: Particles introduced during filling, from a degrading filler neck seal, or rust from inside an older tank can clog the pump's internal filters or the pump inlet strainer (sock filter). This forces the pump to work harder and can starve it of fuel internally, leading to overheating and failure. A severely clogged strainer mimics a pump failure.
  • Water Contamination: Water in the fuel, often from condensation in a frequently low tank or bad gasoline, promotes corrosion inside the pump assembly and does not provide adequate lubrication. It can also freeze in cold temperatures, causing blockages and potential damage. Ethanol-blended fuels can attract more water over time.
• Persistent Running on Low Fuel: While designed to operate at all levels, consistently driving with the fuel gauge near empty (less than 1/4 tank) is detrimental. As mentioned, gasoline acts as a coolant for the pump motor. Low fuel levels mean the pump motor runs hotter, accelerating internal wear and premature failure. It also increases the chance of sucking up sediment that settles at the bottom of the tank, clogging the strainer.
• Failing Fuel Filter (Accelerating Pump Failure): While the fuel pump assembly has an integral inlet strainer, the main fuel filter (located along the frame rail between the tank and engine on the 2004 Impala) is a separate critical component. Its job is to catch finer particles before they reach the fuel injectors. A neglected or clogged fuel filter creates significant resistance in the fuel line. This forces the pump to work much harder against increased pressure to push fuel through, drastically accelerating motor wear and leading to overheating and failure. Changing the fuel filter according to schedule is vital for pump longevity.
• Voltage Supply Problems: The fuel pump requires a stable electrical supply at the correct voltage. Issues within the fuel pump circuit can damage the pump or cause erratic operation:
  • Weak Fuel Pump Relay: A failing relay might intermittently cut power to the pump, causing starting difficulties, stalling, or eventually leading to pump burnout due to erratic operation.
  • Corroded/Faulty Wiring Connectors: Corrosion at the pump connector (often exposed to elements near or on the tank) or along the wiring harness can cause high resistance, voltage drop, or intermittent connection, starving the pump of proper voltage or causing it to fail abruptly. Physical damage to wiring also poses a risk.
  • Blown Fuel Pump Fuse: Obvious loss of power due to a blown fuse prevents the pump from operating at all.
• Age, Mileage, and Natural Wear: Even under ideal conditions, the fuel pump assembly is a mechanical and electrical component subject to finite lifespan. High mileage vehicles naturally have components closer to the end of their expected service life. The pump motor brushes wear down, internal components fatigue, plastic components within the module may become brittle, and seals can degrade over 15+ years.

Professional Replacement Cost Estimate (2004 Impala)

Deciding whether to have a professional mechanic replace your 2004 Impala's fuel pump involves weighing cost against convenience, tool access, and technical comfort. Labor is a significant portion of the total cost due to the complexity of accessing the pump, which requires safely lowering the fuel tank.

• Total Cost Range: A typical professional fuel pump replacement for a 2004 Chevrolet Impala ranges from $450to$850 (USD). This is a widely reported estimate based on industry data and consumer repair order averages. Several key factors cause this variation:
  • Parts Cost & Brand Choice: Mechanics typically mark up parts costs.
    • Economy Level Pumps: Aftermarket brands can start around $100-$200. While potentially meeting minimum specs, quality control, materials, and lifespan vary significantly. Warranties are generally shorter (1-2 years).
    • Standard Quality Aftermarket: More reputable aftermarket brands (like Delphi – often a major OE supplier – Airtex, Carter, Spectra, ACDelco Professional/Gold) offer a better balance of cost and reliability. Expect $150-$350.
    • Premium/OEM-Level (ACDelco): Genuine GM parts (or equivalent OE supplier quality like ACDelco) offer the highest confidence in fitment and longevity but come at a premium: often $300-$550+. Recommended for long-term ownership.
  • Labor Time & Shop Rates: This is where major variation exists. Access requires dropping the fuel tank, a task demanding care and specific steps.
    • Book Time: Professional repair databases (like Alldata or Mitchell) typically quote 2.5 - 4.0 hours of labor for this job on the 2004 Impala. This accounts for depressurization, disconnecting lines/wiring, safely supporting and lowering the tank, module replacement, reassembly, and testing. Note: Rusty tank straps, seized hardware, or other complications can significantly increase this time.
    • Shop Hourly Rate: Labor rates vary dramatically by geographic location, shop type (dealer vs. independent vs. chain), and shop overhead. Rates can range from $90/hour\ast \ast atindependentshopsinlessexpensiveareasto\ast \ast$150+/hour at dealerships or shops in high-cost regions. Multiplying book time by the shop rate gives the labor cost.
    • Potential Additional Fees: Be aware that disposal fees for old gasoline (if the tank must be drained) or hazardous waste fees may sometimes apply.
• Cost Breakdown Example:
  • Scenario A (Lower End): Economy pump ($150)+Labor(2.5hrs@$110/hr = $275)+ShopSupplies/Fees($25) = ~$450
  • Scenario B (Mid-Range): Quality Aftermarket (Delphi/Airtex) ($225)+Labor(3.0hrs@$130/hr = $390)+ShopSupplies/Fees($35) = ~$650
  • Scenario C (Higher End/Dealer): ACDelco OE Replacement ($450)+Labor(3.5hrs@$150/hr = $525)+ShopSupplies/Fees($50) = ~$1025 (This approaches/slightly exceeds the initial high estimate due to top-shelf parts and labor)
• The Value of Diagnosis: Crucially, reputable shops will perform diagnosis before quoting pump replacement. A $150diagnosticfeeismoreprudentthanspending$600+ replacing a pump only to discover the real cause was a bad relay ($20),cloggedfilter($60), or wiring issue. Ensure the shop confirms low fuel pressure via gauge testing or demonstrates circuit failure before proceeding. Request a detailed written estimate breaking down parts and labor.

Detailed DIY Fuel Pump Replacement Guide (2004 Impala - V6 3.8L)

Replacing the fuel pump in a 2004 Impala (specifically the common 3.8L V6 model) is challenging but achievable for experienced DIY mechanics with adequate tools, preparation, and strict adherence to safety protocols. Working with gasoline is inherently dangerous. This guide assumes a base level of auto repair knowledge. Proceed at your own risk. Refer to a repair manual for exact torque specs if available.

• Crucial Safety Precautions (MUST DO):

  • Disconnect the Battery: Start by removing the NEGATIVE (-) battery cable to eliminate any spark risk during fuel system work. Secure it away from the battery terminal.
  • Depressurize the Fuel System:
    • Locate the Schrader valve fuel test port on the fuel rail (under the hood, usually driver's side on the Impala).
    • Cover it with thick rags or safety goggles/shield.
    • Carefully, using a small screwdriver or the valve cap stem, depress the valve core to bleed off residual fuel pressure into the rags. Expect some fuel spray. Have a container ready for the rags.
  • Work in Well-Ventilated Area: Gasoline fumes are highly explosive and toxic. Ensure maximum airflow – ideally outdoors or in a large open shop. Have a fire extinguisher rated for gasoline fires (Class B) immediately accessible.
  • No Open Flames or Sparks: Prohibit smoking, pilot lights, electrical tools that could spark, or any other ignition source anywhere near the work area.
  • Drain the Fuel Tank:
    • This is highly recommended but adds significant complexity. Methods include:
      • Siphoning carefully through the filler neck (Difficult due to anti-siphon devices).
      • Using the fuel pump itself: Temporarily reconnect the battery positive only, jumper the fuel pump relay socket to run the pump (details vary - research specifics for your Impala), and run the pump output hose into a large, approved gasoline container until empty. Disconnect battery again immediately after. Preferred DIY method if viable.
      • Removing the tank with fuel inside: NOT recommended. It's extremely heavy and sloshing fuel poses a major safety hazard and spill risk during removal.
  • Wear Safety Glasses: Protect your eyes at all times.

• Required Tools and Materials:

  • New fuel pump module assembly (V6 3.8L specific - confirm part#)
  • Floor jack and strong jack stands (minimum 2-ton rating)
  • Wheel chocks
  • Socket wrenches (SAE and Metric sockets – typically 13mm, 15mm, 18mm common)
  • Ratchet wrenches, long extensions
  • Torque wrench (recommended for tank strap bolts)
  • Wrenches (combination or flare nut for fuel lines)
  • Fuel line disconnect tools (GM quick-connect style – multiple sizes)
  • Screwdrivers (flathead and Phillips)
  • Needle nose pliers
  • Brake cleaner & shop towels
  • Drain pan or large container for residual fuel
  • New locking fuel cap seal ring (often required when opening the pump assembly – kit may include one)
  • Nitrile gloves

• Step-by-Step Procedure:

  1. Prepare Vehicle: Park on a flat, level, solid surface. Chock the rear wheels securely. Engage the parking brake firmly.
  2. Siphon/Gas Drain: Implement your chosen method to remove as much gasoline as safely possible.
  3. Disconnect Battery: Remove negative (-) battery terminal.
  4. Access Fuel Tank: The tank is under the rear seat area.
     • If needed: Lower rear seats.
     • Locate the access panel on the trunk floor above the fuel tank/pump area (may require trunk carpet removal). The 2004 Impala's pump is accessed by lowering the entire fuel tank from underneath the car. There is usually no interior access panel above the pump/sending unit in this model year. Proceed to tank lowering.
  5. Access Pump Module Below (Tank Must Be Lowered):
     • Safely lift the rear of the car with the floor jack, supporting it securely on jack stands under the manufacturer recommended lift points (NOT on the tank, tank straps, or suspension). Leave enough room under the rear axle/differential to work.
  6. Identify and Loosen Tank Straps: Locate the two large steel straps holding the tank up against the car's frame rails. The front strap typically bolts to a bracket; the rear strap bolts directly to the frame or crossmember. Note their position. Remove the retaining nuts/bolts using the correct size sockets/extensions (commonly 15mm or 18mm). Support the tank with a second jack and a wide wood block before fully removing the last bolt/nut on each strap.
  7. Disconnect Fuel Lines and Wiring:
     • Electrical: Locate the main wiring harness connector on the driver's side top front of the tank. Press any locking tabs and disconnect it. Feed the harness connector through its retaining bracket.
     • Fuel Lines: Identify the fuel lines running to the top of the tank (Feed and Return lines, potentially also an Evaporative Emission line). These have quick-connect fittings. Know the correct disconnect tool size(s) required.
       • Carefully pry off the blue (feed) and green (return) retaining clips (if present) using needle nose pliers or a small screwdriver – save them! Not all Impalas had these clips.
       • Push the correct fuel line disconnect tool firmly into each fitting around the fuel line, sliding it fully onto the collar. You might feel/hear a slight click.
       • While holding the tool in place, sharply push the fuel line connector towards the tank (compressing the retaining barbs), and simultaneously pull the line away from the tank. The tool should hold the collar back as the line slides off the fitting.
       • Expect residual fuel drip/splash – have rags and the drain pan positioned. Keep the open ends of the lines/connectors clean and plug them if possible.
  8. Lower Fuel Tank: With the straps removed/loosened, lines and wiring disconnected, and the tank supported by the secondary jack/block, slowly and carefully lower the tank several inches. Keep it level to prevent fuel spillage.
  9. Remove Pump Locking Ring:
     • The pump assembly is held inside the tank with a large, threaded plastic locking ring. It often has tabs.
     • Use a brass drift punch and hammer (to avoid sparks) or specialized fuel tank wrench/spanner tool to gently tap the ring counter-clockwise (lefty-loosey) until it disengages. It can be very tight. Never use a steel chisel or excessive force.
  10. Remove Old Fuel Pump Module: Once the ring is loose, lift it off. Reach inside and carefully pull the entire pump assembly upwards and out of the tank. Guide it through the opening. Be careful not to damage the fuel level sensor float arm. Note its orientation.
  11. Inspect & Replace Strainer/Gasket:
      • Transfer the brand new strainer (sock filter) from your replacement pump kit to the old position on the bottom inlet of the new pump module. Press it firmly onto the inlet tube (ensure internal O-ring seats correctly).
      • Place the new black sealing ring gasket (included with pump kit) around the opening in the fuel tank. Do NOT use petroleum-based lubricants on this gasket.
      • Carefully clean the tank sealing surface around the opening with a lint-free cloth and brake cleaner.
  12. Install New Fuel Pump Module: Align the new pump assembly exactly as the old one came out. Gently rotate the float arm slightly if needed to clear the tank opening. Lower it straight down into the tank. Ensure the module flange is seated flush onto the new gasket.
  13. Install Locking Ring: Place the large plastic locking ring onto the tank opening, aligning its tabs/lugs. Carefully tap it clockwise (righty-tighty) with the brass punch or spanner wrench until it's securely seated and hand-tight. Avoid overtightening which can crack the ring or tank.
  14. Raise Tank Partially: Carefully jack the tank back up near its original position. Don't secure straps yet.
  15. Reconnect Lines and Wiring: Guide the wiring harness connector back through its bracket and firmly push it together until it clicks locked. Ensure any retaining clip engages properly on the connector body. Reconnect the fuel lines:
      • Ensure their O-rings are present and lubed with a drop of fresh oil or silicone grease only if recommended by the manufacturer.
      • Push the quick-connect fitting squarely onto the pump module's hard line until it fully seats. You should feel/hear a distinct 'click' as the internal barbs lock over the ridge on the hard line. Tug firmly on the fuel line to ensure it's locked. Reinstall the blue/green plastic retaining clips (if applicable). Double-check every connection.
  16. Secure Tank Straps & Jack: Position the tank straps correctly in their brackets/hangers. Install the strap bolts/nuts and tighten them gradually and evenly using the torque wrench (refer to manual if possible, otherwise to a firm, snug fit). Ensure the straps are positioned correctly and hold the tank securely against its rubber mounts. Slowly lower the secondary support jack away.
  17. Final Tank Position Check: Visually confirm the tank is secure. Re-check all connections for good measure.
  18. Lower Vehicle: Safely remove jack stands and lower the vehicle.
  19. Reconnect Battery: Reattach the negative battery terminal.
  20. Prime the System: Turn the ignition key to the "ON" position (do not start) for 2-3 seconds, then OFF. Repeat this 2-3 times. This runs the fuel pump briefly to pressurize the system. Listen for the pump running normally at the rear. Check for leaks immediately around the pump access area and under the hood at the fuel lines/rail.
  21. Start Engine: Attempt to start the engine. It may crank slightly longer than usual as air purges from the lines. Monitor for smooth idle and no leaks.
  22. Test Drive: Conduct a short test drive at low speed first, checking for proper performance and leaks. Pay attention to gauge readings and acceleration.
  23. Reseal Trunk: Reinstall trunk flooring/carpet and rear seat.

• Critical Considerations:

  • No Interior Access: Unlike some vehicles, the 2004 Impala requires lowering the fuel tank for pump access. No easy under-rear-seat panel exists.
  • Confirm V6 vs. V8: The LS4 V8 engine in rare SS models uses a different fuel pump assembly than the V6. Ensure you order the correct part.
  • Complexity: This is a demanding job physically, requires specialized tools (disconnect tools), and has significant safety hazards. Assess your skills realistically. Hiring a professional is often the wiser choice.
  • Potential Tank Rust: Older vehicles in northern climates often have rusty tank straps, bolts, or shields. PB Blaster or other penetrant oil applied hours beforehand is essential. Broken bolts or hardware add significant difficulty.

Preventative Maintenance Tips to Protect Your Fuel Pump

Proactive care significantly extends the service life of your 2004 Impala's fuel pump. Implementing these straightforward practices reduces stress on the pump, minimizes contaminant risks, and contributes to overall fuel system health.

• Avoid Persistent Low Fuel Levels: Make it a habit to refill your tank before it drops below the 1/4 mark. Consistently running on less than 1/4 tank causes two major problems:
  1. Overheating: Gasoline submerging the pump motor acts as a primary coolant. Lower fuel levels mean less coolant, leading to excessive heat buildup inside the motor windings. This heat degrades internal components, electrical insulation, and bearings much faster.
  2. Sediment Intake: Debris like rust particles, dirt, and gum/varnish naturally settle to the tank bottom. A low fuel level increases the pump's suction inlet drawing in this concentrated sediment load, potentially clogging the inlet strainer ("sock") quickly and forcing the pump to work much harder, accelerating wear. While the sock filters out large particles initially, fine sediment bypasses it. Aim to keep the tank above 1/4 full whenever practical.
• Replace the Fuel Filter at Recommended Intervals: The Impala's inline fuel filter (located along the frame rail) is a critical but often neglected maintenance item. Its primary job is to trap fine contaminants before they reach the expensive fuel injectors. A major secondary benefit is protecting the fuel pump. As the filter clogs over time:
  • Increased Pump Stress: The pump must generate much higher pressure to force fuel through the restricted filter. This extra workload causes the pump motor to draw higher current, overheat, and wear out prematurely. Filter replacement intervals are typically every 30,000 - 40,000 miles, but always consult your specific Impala's owner's manual or a trusted shop recommendation. Replacing a $20-$40 filter is far cheaper than a new fuel pump. It's a vital safeguard.
• Utilize Reputable Gas Stations: While fuel quality regulation exists, variation occurs. Choosing well-maintained, high-volume stations with trusted brands reduces the risk of filling up with contaminated gasoline (dirt, water, tank residue). Stations known for water intrusion or dispensing problems should be avoided, especially when they've recently received a fuel delivery which can stir up tank sediment.
• Address Check Engine Lights Promptly: Don't ignore that illuminated CEL. While a failing fuel pump doesn't always trigger a direct code initially, codes pointing to fuel trim issues (P0171/P0174 - lean condition), fuel circuit malfunctions (P0230), or low fuel pressure (P0087) require investigation. Ignoring underlying issues like clogged injectors, faulty fuel pressure sensors, or even oxygen sensor problems places abnormal loads on the pump or masks early signs of its decline. Early diagnosis often prevents secondary failures and bigger bills.
• Consider Fuel System Cleaners (Use with Caution): Opinions vary on fuel additives. Using a reputable fuel injector cleaner periodically (like Techron Concentrate or Red Line SI-1) as part of routine maintenance may help prevent carbon buildup on injectors and maintain overall fuel system cleanliness. However:
  • Avoid "Miracle Cure" Claims: No additive will revive a physically damaged or dying fuel pump.
  • Check Ingredients: Some strong detergents in cheap cleaners can dislodge large amounts of varnish or debris suddenly, potentially overwhelming the fuel filter or pump strainer. Stick with well-established brands following the product instructions.
  • Not a Fix for Existing Problems: If you already have symptoms (hard start, hesitation), cleaners won't fix them – diagnosis is needed.

Professional Diagnosis: Before Spending on Replacement

Before committing to the cost and effort of fuel pump replacement, a professional diagnosis is a crucial step. Symptoms that seem like a classic pump failure might stem from other, less expensive problems within the fuel system or related electrical circuits.

• The Importance of Confirmation: Replacing a fuel pump is a major service. Skipping proper diagnosis risks replacing a perfectly good pump only to find the original problem remains, wasting significant time and money. Professional technicians possess the specific tools and knowledge to pinpoint the actual cause.
• Critical Step: Fuel Pressure Test: This is the most definitive test for the health of the pump itself.
  • Locate Test Port: The technician finds the Schrader valve fuel pressure test port on the engine's fuel rail (looks similar to a tire valve).
  • Connect Gauge: They securely attach a dedicated fuel pressure gauge specifically designed for automotive systems.
  • Measure Pressure: Key cycles, running pressure, and pressure decay are tested:
    • Key On (KOEO - Key On Engine Off): Check for the initial priming pressure build-up (should be around 55-62 PSI for the 2004 Impala 3.8L) and that it holds steady without significant immediate leakdown after pump shuts off.
    • Engine Running: Verify pressure remains stable (typically within 5 PSI of the KOEO prime pressure, still around 50-60+ PSI) across various RPM ranges (idle and under moderate load).
    • Engine Off (Pressure Hold): Check if pressure holds reasonably well for several minutes after engine shutdown. Excessive pressure bleed-down indicates a weak pump check valve or potentially a leaky injector (the latter requires additional tests).
  • Interpret Results: Low pressure during KOEO or running confirms a fuel supply issue (pump, major restriction, regulator). Good pressure that drops excessively during running might point more towards injector leakage or regulator problems. No prime pressure points squarely at pump failure or circuit issues.
• Check Fuel Pump Circuit: Measuring pressure requires the circuit to work. If the pump does nothing (no priming sound):
  • Verify Fuse: Check the fuel pump fuse(s) in the underhood fuse box for continuity or visual signs of being blown. Replace if necessary.
  • Test Relay: Locate the fuel pump relay (often labeled "FP" in the underhood fuse box). Technicians test it by swapping it with an identical, known-good relay (like the horn relay) or using a relay tester/multimeter to check for switching functionality and contact integrity. A weak or failed relay is common.
  • Test Voltage at Pump Connector: If fuse and relay are good, the next step requires accessing the wiring harness connector near the fuel tank. With the fuel pump circuit activated (key ON or during engine cranking), a multimeter is used to measure voltage at the pump connector. Correct voltage indicates the wiring is delivering power. Absent or low voltage points to a wiring or grounding fault upstream. Correct voltage with a silent pump confirms pump failure.
• Scan for Diagnostic Trouble Codes (DTCs): Technicians use an OBD-II scanner to retrieve stored or pending codes. While not definitive for the pump itself, codes like P0230 (Fuel Pump Primary Circuit), P0087 (Fuel Rail Pressure Low), or persistent P0171/P0174 (Lean Condition) provide valuable context and guide testing towards the fuel delivery system. Absence of codes doesn't rule out the pump, but presence guides the diagnostic path.
• Visual Inspection: Check around the fuel lines under the car and near the tank for visible fuel leaks. While a leak isn't the pump failing per se, it certainly causes fuel pressure loss and must be repaired. Examine wiring harnesses near the tank for damage, rodent chewing, or corrosion.

Conclusion: Addressing a Critical System

A failing fuel pump in your 2004 Chevrolet Impala is a significant failure that demands attention. Recognizing the symptoms – crank/no start, stalling, hesitation, loss of power under load – is the critical first step. While professional replacement typically costs $450-$850 depending on parts choice and labor rates, the job, requiring fuel tank lowering, is achievable by experienced DIYers willing to prioritize safety. Prevention through avoiding consistently low fuel levels, replacing the fuel filter regularly, and using quality fuel goes a long way in extending pump life. If symptoms appear, investing in professional diagnosis ($100-$150) before committing to pump replacement saves time and money by ruling out simpler problems like a blown fuse or faulty relay. Addressing a failing fuel pump promptly ensures your Impala retains the reliable performance it's known for.