Protecting Engines and Businesses: How DENSO Fights Spark Plug Counterfeiting
As a global OEM and aftermarket supplier, DENSO continuously implements countermeasures to protect customers and partners from counterfeit products, while educating the market on how to recognize and avoid them.
Why counterfeit spark plugs are dangerous
Spark plugs play a critical role in engine performance, influencing combustion efficiency, fuel consumption, emissions, and cold-start reliability. Counterfeit spark plugs often use inferior materials, imprecise manufacturing processes, and low-quality electrodes. As a result, they can cause misfires, unstable engine operation, overheating, and in severe cases, damage to ignition components or the engine itself like damage to the cylinders, pistons and therefore to expensive engine disassembly and repair.
Key indicators of genuine DENSO spark plugs
One of the most reliable ways to verify authenticity is careful inspection. Original DENSO spark plugs feature an ultra-thin center electrode with precise geometry, ensuring stable ignition and long service life. In counterfeit products, the electrode is typically thicker and poorly finished.
Centre electrode on iridium spark plugs
Deviation from the specified center electrode diameter is one of the key indicators of a counterfeit. Genuine DENSO iridium spark plugs feature an ultra-thin electrode with precise geometry, ensuring stable ignition and long service life.
In counterfeit products, the electrode diameter is typically increased to 0.6–0.8 mm, whereas in original products it can be as small as 0.4 mm depending on the part index. Welding quality is often rough and uneven. Such deviations directly affect durability and increase the likelihood of warranty claims.
Note:
Reference values depend on part number markings:
- D / S – 0.7 mm
- F / Z – 0.55 mm
- I / V / SV – 0.4 mm
Another important reference is the part number, which serves as a technical specification. Errors in part number structure, inconsistent markings, or low-quality printing should always raise concerns.
The country of origin is also a critical factor. DENSO spark plugs supplied through official channels are manufactured at DENSO plants in Japan, Indonesia, China and USA only. Any deviation from this information requires additional verification.
Scratch test
A simple scratch test can also help identify suspicious products. Genuine DENSO spark plugs feature a durable surface coating. If the coating scratches easily and reveals a copper-colored layer underneath, authenticity should be questioned and the batch requires additional inspection.
How to avoid counterfeit products
The most effective way to minimize the risk of counterfeit spark plugs is to purchase products exclusively through authorized distribution channels. Trusted supply chains ensure that spark plugs meet DENSO’s strict quality, performance, and safety standards.
For distributors and workshops, implementing systematic checks during purchasing and goods receipt significantly reduces the likelihood of counterfeit products entering circulation. End customers are strongly advised to avoid unofficial sources online retailers and marketplaces that may offer products at unusually low prices without traceable origin.
To ensure you are buying genuine DENSO spark plugs, always purchase from our authorized distributors.
Use DENSO’s official Where to Buy tool to find a verified distributor near you.
For more tips on how to Identify counterfeit, download the technical poster or watch the movie:
