Why is My 2013 Honda Accord Getting Bad Gas Mileage?

The Basics

Poor fuel economy, or getting fewer miles per gallon (MPG) than you expect, is one of the most common and frustrating car problems. It hits your wallet directly every time you fill up. While your vehicle's official EPA rating is a guideline, a significant and sudden drop in MPG is a clear sign something is wrong. Based on an analysis of 100 owner discussions, this issue is rarely caused by just one thing. Instead, it's often a combination of mechanical problems, maintenance oversights, and driving habits that slowly drain your tank faster than it should.

Common Indicators

Owners reporting poor fuel economy typically notice a few clear signs. The most obvious is simply needing to fill up the gas tank more often for your regular commute or trips. You might see the estimated "miles to empty" on your dashboard drop faster than the miles you're actually driving. Many people report calculating their MPG manually after a fill-up and finding it's 3-5 MPG (or more) lower than their car's historical average or the advertised rating. Sometimes, this is accompanied by other subtle symptoms like the engine feeling slightly sluggish or a check engine light, but often the poor MPG is the only noticeable complaint.

What's Behind It

Based on confirmed fixes and owner reports from the discussions, poor fuel economy usually stems from issues that force your engine to work harder or burn fuel less efficiently. A frequent culprit is a faulty oxygen sensor, which can trick the engine computer into using too much fuel. Dirty or failing fuel injectors that don't spray fuel properly are another common cause. Problems with the ignition system, like worn spark plugs or bad coils, lead to incomplete combustion, wasting fuel. Even simple things like under-inflated tires create more rolling resistance, and a dirty air filter chokes the engine, making it less efficient. While not as common in the data, some owners found that failing components like the alternator or starter motor, by placing a constant heavy electrical load on the engine, can also contribute to reduced MPG.

Identifying the Cause

Pinpointing the exact cause requires a bit of detective work, starting with the simplest checks. First, check your tire pressure with a reliable gauge—this takes two minutes and is a top offender. Next, scan for diagnostic trouble codes (DTCs) with an OBD-II scanner. A code like P3497 (which relates to valve control) or any oxygen sensor or fuel trim codes can point you directly to an electronic or emissions fault. Listen for any unusual engine sounds and note if the problem started suddenly or crept up over time. If there are no codes, consider your maintenance history: when were the spark plugs, air filter, and fuel injectors last serviced? A professional can perform a fuel pressure test and a smoke test to check for vacuum leaks, which are harder to find at home.

What Actually Works

Here are the solutions ranked by how often they worked for owners, starting with the simplest and most affordable.

1. Correct Tire Pressure & Remove Excess Weight: This was the most frequent simple fix. Ensuring all tires, including the spare, are inflated to the manufacturer's recommended PSI (found on the driver's door jamb) can improve MPG by 3-4%. Also, clean out your trunk—hauling around unnecessary weight makes your engine work harder.
2. Routine Maintenance Replacement: Replacing a clogged engine air filter, worn spark plugs, and using a quality fuel injector cleaner can yield noticeable improvements. Many owners reported a 1-3 MPG gain just from catching up on this basic upkeep.
3. Address OBD-II Trouble Codes: If you have a code, fix what it indicates. Replacing a faulty oxygen sensor is a very common and successful repair for restoring lost MPG. Ignoring these codes almost always means continued poor efficiency.
4. Check for Drains on the Engine: If basic maintenance doesn't help, consider the alternator and battery. A failing alternator working overtime to charge a weak battery puts a constant mechanical load on the engine, hurting fuel economy. Have your charging system tested.
5. Professional Diagnostics for Persistent Issues: For problems that remain after the above steps, a shop can diagnose issues like a failing catalytic converter, improper wheel alignment, dragging brakes, or sophisticated engine management problems that are difficult to identify without advanced tools.

Repair Costs

Costs can vary widely based on the cause and whether you do it yourself (DIY) or use a professional shop.

• DIY (Low Cost): Inflating tires is free. An air filter costs $15-$30, spark plugs $25-$80 for a set, and a bottle of fuel injector cleaner $10-$20. A basic OBD-II scanner is a $30-$60 investment that pays for itself.
• DIY (Moderate Cost): Replacing an oxygen sensor typically costs $50-$150 for the part and is a manageable job with basic tools. A set of hubcaps (sometimes called wheel covers) is purely cosmetic and won't affect fuel economy unless you're replacing heavy aftermarket wheels with lighter OEM ones.
• Professional Repair: Labor adds significantly. Oxygen sensor replacement at a shop: $150-$300. Fuel injector service: $200-$500. Alternator replacement: $400-$800. Addressing a catalytic converter or complex emissions issue (like code P3497) can run from $600 to over $2,000, depending on the vehicle.

The golden rule is to start with the no-cost and low-cost checks before moving to more expensive diagnostics and repairs.

Preventive Measures

The best way to avoid poor fuel economy is consistent, proactive maintenance. Stick to your vehicle's scheduled service intervals for oil changes, air filter replacement, and spark plug changes. Check your tire pressure at least once a month and especially with seasonal temperature changes. Use quality fuel and consider a fuel system cleaner every 5,000-10,000 miles. Pay attention to your driving style—rapid acceleration and high-speed driving are major fuel wasters. Finally, don't ignore a check engine light; getting it checked early can prevent a small, inexpensive problem from snowballing into a major repair and months of wasted fuel.

Source Summary: This analysis is based on 100 owner discussions from Reddit and automotive forums.