The rise in counterfeit parts globally poses a real risk to the entire independent supply chain, from manufacturers to distributors and, critically, from workshops to customers as well. DENSO looks at the challenges posed by counterfeit spark plugs and advises the aftermarket on how to counter them.

As internet shopping and e-commerce have become a prominent feature of people’s lives, motorists and technicians alike now have access to a global marketplace for vehicle components. At times, the lure of purchasing a part online for less than paying a distributor, or fitting customer-supplied parts, may seem like good business, but it could be putting the health and safety of customers at risk.

Unfortunately, too often, counterfeit items from virtually every product category are found throughout legitimate marketplaces, with some technicians unwittingly exposing customers to sub-standard products. 

Often it can be difficult to identify a counterfeit part, particularly if ordering online with just a small image to go by. Counterfeiters are becoming highly-skilled in making non-genuine parts and their packaging look identical to genuine ones. While some parts may look the same as genuine parts, they are unlikely to perform to the same standard and in many cases, counterfeits will have been produced using inferior materials, which will not have been rigorously tested for safety. This is a particular issue with counterfeit spark plugs, which can cause a major drop in engine power under heavy acceleration or load. If these plugs overheat, they can melt and cause considerable engine damage, costing a driver thousands of pounds and potentially costing a technician their business.

How to avoid counterfeit parts 

When sourcing a part, technicians should only ever purchase from a recognised, authorised distributor. While e-commerce websites may appear to have great deals and low prices, too often a deal that looks too be good to be true will be – and could prove a disappointing purchase.

To demonstrate the differences between authentic products and counterfeits, DENSO has created several comparisons to help technicians identify a genuine DENSO spark plug.


One of the biggest signs of a purchased counterfeit spark plug is the difference in how the product may look. Simple things, such as the branding embossing containing typos or spelling mistakes is an indication of a non-genuine part. A genuine DENSO spark plug should have a uniform insulator shape, be white in colour, and the width of the ground electrode should be consistent. Poor quality welding is something to look out for, while spark plugs with ground electrode chips made from poorer materials should also be avoided. A quick scratch test can reveal if mediocre materials have been used, indicating a non-genuine or counterfeit part.


The packaging may also contain some obvious signs that the spark plug is not a genuine DENSO part. DENSO spark plugs are only manufactured in Japan, Indonesia, China or the United States of America. If a part claims to be a DENSO component but has been manufactured outside of these areas, then it is not genuine. Counterfeit spark plugs may also have subtle differences in the logo; the DENSO arc should always be positioned towards the left-hand side of the box, for example. Poor print quality, differences in the label cutting and folding also indicate a fake.

Another item to check is the barcode and production code. DENSO products have complete traceability throughout the supply chain, and non-matching production codes are likely to indicate counterfeits. Technicians should always check the barcode number and if in doubt, they should call their local DENSO representative who can advise.

Technical specification

All DENSO parts go through a stringent manufacturing process to ensure the highest quality every time. Checking spark plugs against official specifications in the DENSO catalogue is a simple and effective method of identifying a counterfeit. There are several checks technicians can carry out:

The issue of counterfeit parts is one that is not going away, with several industry bodies and organisations working to highlight the issue and protect manufacturers, workshops and motorists. The best way to avoid unwittingly purchasing and fitting a counterfeit part is to only buy through official DENSO channels and exercise due diligence when doing so.

More information on identifying counterfeit spark plugs:

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