I've been chasing down an unexpected technical deficiency I've spotted on my Kona EV and thought I would be remiss if I did not take the time to alert owners of the above vehicles because they may be similarly affected.

To be clear, this has not caused my Kona EV to break down or caused any noises (by 19,000 km) but the potential service life would certainly have been shortened, and the likelihood of a future gear reducer failure increased. This may or may not be related to the few complaints of knocking noises, nothing like that is implied as of yet.

So, I personally acquired power transmission troubleshooting experience way back in the early '80s in the UK where I worked as a technical services engineer in a firm that manufactured and installed engine and gearbox dynamometer test facilities for automotive, aerospace and industrial customers worldwide. I was the guy that had to figure out where our machine designers had screwed up and come up with practical solutions that could be applied in the field.

In essence the gear reducer in the Kona is not equipped with the most basic form of ferrous particle filtration commonly fitted to all simple splash-lubricated gearboxes with steel gears, otherwise known as a magnetic drain plug. The Series II is the same according to the experience of one helpful owner in Australia with only 3,700 km.

The end result is that steel particles that normally wear off gears (especially during the first 1,000 km) will continue to circulate in the gear oil and pass through the precision ball and tapered-roller bearings over and over. They'll get crushed down to a fine dust, discolouring the oil and adding unnecessary wear to the bearing raceways.

On every EV with the same deficiency the factory oil will come out looking like black coffee by 4,000 km and contain fine ferrous particles. I've found that two oil changes will clear that up.

Unfortunately, I don't have an easy way to determine which vehicle models are affected and the only way to find out is to change the oil. But frankly I'm pretty sure all those I've listed are affected.

The minimum course of action I'd suggest for owners of these vehicles to take is to change the gear reducer oil as soon as practical at your expense.  Anytime after 1,000 km is appropriate. That will rid the lubricant of most of the unwanted contaminants.  I believe that this one step will significantly lessen the risk of problems down the road. You can also verify whether or not you already have a magnetic drain plug installed.

Several owners outside of NZ have reported difficulties getting dealers to carry out this relatively-simple job because it's not scheduled maintenance until 120,000 km. One dealer did not believe that an EV even had oil in it. Another dealer did not have a standard billing category so they ended up using a "diff oil change" as it's similar.  Dealers have the appropriate oil as it's used in DCT transmissions as well.

The job is easy enough to DIY for those experienced and if that's on the table for anyone I'll outline the steps on request. I've done it four times now.

Diligent owners may want to also get ongoing oil changes at the major service intervals, or consider adding a magnetic drain plug if your car is out of warranty and you're willing to take any attendant risks.