INFINITI Q40 Spark Plug Replacement Guide (2015)
Keep your Q40's VQ37VHR engine running smoothly with the right spark plugs.
- Stick with OEM-spec Denso or NGK Iridium spark plugs for the best performance and longevity.
- Always replace spark plugs as a full set of six to ensure balanced engine performance.
- Plan to replace the two throttle body gaskets during the job to prevent future vacuum leaks.
- The job is more complex than on other cars; accessing the rear plugs requires removing the throttle bodies.
Symptoms of Failing Spark Plugs in a Q40
When your Q40's spark plugs are nearing the end of their 105,000-mile service life, you'll likely notice a few key symptoms. Ignoring them can lead to poor performance and potentially damage other engine components.
- Rough Idle: The engine may shake or vibrate more than usual when you're stopped.
- Engine Misfires: You might feel a hesitation or stumbling during acceleration. This can trigger the Check Engine Light with codes from P0300 to P0306.
- Reduced Fuel Economy: If you're filling up your tank more often, worn plugs could be the cause due to inefficient combustion.
- Difficulty Starting: The engine may take longer to crank before it starts, especially in cold weather.
- Poor Acceleration: A noticeable loss of power when you press the gas pedal is a common sign of a weak spark.
Choosing the Right Aftermarket Spark Plugs
Since the 2015 Q40 is mechanically identical to the G37, it uses the same high-performance VQ37VHR engine. This engine requires high-quality Iridium spark plugs for longevity and performance. You don't have to buy them from the dealer to get excellent quality.
| Brand Tier | Brands | General Assessment |
|---|---|---|
| OEM / Top Tier | Denso, NGK | The original factory spark plugs are Denso Iridium plugs (Part No. FXE24HR11). Both Denso and NGK are highly recommended by owners and mechanics for their perfect fit and long service life. You can consider these as direct OEM replacements or even an upgrade if you choose a model like the NGK Ruthenium. |
| Reliable Aftermarket | Bosch | Bosch offers Double Iridium spark plugs that are a reliable and cost-effective alternative to the OEM brands. They meet the performance requirements of the VQ37VHR engine and are a solid choice for daily driving. |
| Budget-Friendly | Champion | Champion provides Iridium plugs that will get the job done at a lower price point. While they are a functional option, most enthusiasts and long-term owners of Infiniti vehicles tend to prefer Denso or NGK for peace of mind. |
Pro Tip: Check for Oil
When you remove the old spark plugs and ignition coils, check the spark plug tubes for oil. If you find oil, it's a clear sign that your valve cover gaskets are leaking. Since you've already done most of the disassembly, it's the perfect time to replace the valve cover gaskets to prevent future misfires.
🎬 See how to replace leaking valve cover gaskets on this engine.Installation Tips and Known Issues
Replacing the spark plugs on the Q40's 3.7L V6 is more complex than on a typical four-cylinder engine. To access all six plugs, you must remove the dual air intakes and both electronic throttle bodies. 🎬 Learn how to properly clean your throttle bodies while they're removed. This makes the job moderately difficult for a DIYer.
🎬 Watch this step-by-step spark plug replacement guide for your Q40.Warning: Always replace the two throttle body gaskets when you perform this job. Reusing old gaskets can cause vacuum leaks, leading to a rough idle and a Check Engine Light. Also, be gentle with the PCV hoses, as they can become brittle and crack with age.
Frequently Asked Questions (FAQ)
Do I need to gap the new spark plugs?
No. The recommended Iridium spark plugs from Denso and NGK come pre-gapped from the factory. Do not attempt to change the gap, as you can easily damage the fine Iridium tip.
Should I replace the ignition coils with the spark plugs?
It's not required. Unlike spark plugs, ignition coils are not considered a standard maintenance item and should only be replaced if they fail. However, if you have a misfire code for a specific cylinder and you're already replacing the plugs, it can be cost-effective to replace the failing coil at the same time.
How difficult is it to replace the spark plugs myself?
For an experienced DIY mechanic, it's a manageable task that takes 2-3 hours. For a beginner, it can be challenging due to the need to remove the throttle bodies to access the rear plugs. You will need a specific 14mm magnetic spark plug socket, a torque wrench, and various extensions.
Are there any recalls for the 2015 Q40 spark plugs?
No, there are no recalls or technical service bulletins (TSBs) from INFINITI or the NHTSA related to the spark plugs for the 2015 Q40.
Helpful Videos
Technical Specifications
OEM Part Numbers: 22401-JK01D
Engine: 3.7L V6 (VQ37VHR), Quantity Required: 6, Plug Type: Iridium, OEM Brand: Denso (FXE24HR11), Socket Size: 14mm
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
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