Preventive Maintenance of EVs

Dec. 4, 2023
When you are performing the task of preventive maintenance, you will be much better at it if you have a working knowledge of the system you are maintaining. Electric vehicles (EV) can gain more range with thoughtful preventive maintenance (PM).

When you are performing the task of preventive maintenance, you will be much better at it if you have a working knowledge of the system you are maintaining. Electric vehicles (EV) can gain more range with thoughtful preventive maintenance (PM). Every EV will develop pattern failures over time. When this happens, most OEMs send out a technical service bulletin (TSB). Understanding them can add to the PM, as a software update can also be considered maintenance. Studying specific EVs will enhance your preventive maintenance work.

What is considered preventive maintenance? Is it only what the OEMs have written in the owner’s manual or could it be more? A typical owner’s manual is installed in the glove box of every new vehicle and is often 500 pages, or more today. Once the EV is resold as a used vehicle, the manual may be on eBay and the second owner does not have it for reference. When the owner of an EV does not know what to do, it is often the service advisor who will suggest what is needed. Did you know most owner’s manuals are free online as a PDF download? Go to for more information. All vehicles need more preventive maintenance than most OEMs suggest, even the electric ones.

When the suggested preventive maintenance work order is given with pricing to the owner of a vehicle, the owner needs to understand that the cost of the work is worth it, as it will prevent more expensive repairs later on. It also keeps the vehicle in top shape so that it is safer and gets better fuel economy (electrical fuel). These are all positive results. Do all customers practice preventive maintenance? No, but a well-trained technician can help by suggesting it, and if the shop has a program in house that keeps track of each customer’s vehicles, the process is easy. Fleet managers are good at preventive maintenance, as they keep records of the maintenance required and in turn that keeps commercial vehicles on the road and not in the shop.

There is a gray area between “repair work” and “preventive maintenance”. Keep reading and we will cover the recommended PM as well as additional work.

Preventive Maintenance Possibilities

If we look at pure electric vehicles sold today, like a Nissan Leaf, Tesla Model 3 or Kia Niro EV (the ACDC fleet includes all of these vehicles, plus others), what will a preventive maintenance inspection look like? They still have tires and brakes so alignments are still needed, as are tire rotations, air pressure checks and balancing. Brake fluid still exists. Coolant will be on board to cool down the high voltage inverters, DC-DC converter, on-board HV battery and its charger, drive motor(s) and such, but that antifreeze mixture will last much longer than in an internal combustion engine (ICE). Wiper blades will still streak and washer solvent will run dry. Lights need to be checked but most will be LED, so as not to drain the HV battery pack as much as the old fashioned “glowing elements of tiny wires.” The transmission is gone (as is the ICE) but a gearbox of sorts will exist. It will be a gear reduction unit, with a differential built in, that connects the electric drive motor to the wheels. That gear box fluid will need a change somewhere in its service life. Most will require that service at 10 years or 150,000 miles. Presently wheel hub motors are not used. Most EVs have one brushless electric motor driving either the front or rear wheels — two if it is AWD. A few light duty trucks will have four drive motor assemblies, one for each wheel with a short drive shaft to each wheel.

The coolant that takes heat away from the high voltage parts will need replaced. That waste heat was not used to heat the cabin until Tesla, in M/Y 2020, installed a unique heat pump on the Model Y. It had an eight-way valve, commonly called the “octovalve” system. Before that, the waste heat from the drive system was not used for cabin heat as it was erratic, so EVs needed a supplemental heater to warm the occupants. There are four types of cabin heat:

  • heating coolant with HV in a small tank,
  • heating cabin air with a HV grid,
  • heat pump with a back HV grid, and
  • heat pump with “octovalve.”

There may be more to come. Make sure you read and understand the thermal systems in modern EVs to know what to do to maintain them. You will see a “flush and fill” but at long intervals. The A/C system is much like a hybrid vehicle with an electric compressor so A/C work stays the same, unless you have a heat pump system.

Private Owner Customers

When a new owner of any EV comes in for service, it is a good time for the service advisor to educate them about the PM needed. Most EV owners think there is nothing to do at all to take care of their car or truck. Not true. Talk to them about their concerns and get a complete history of their electric vehicle. If you take great care of them, and their vehicle, they will send more people to your shop and that is good for everyone.


If you have fleet customers, the technician’s job is to keep the fleet vehicles operating safely, cleanly and reliably. Downtime is a big problem for fleets. It goes way beyond preventive maintenance, so if you see something that could cause a breakdown, let the fleet manager know. Communication is key between the EV fleet technician and fleet manager. The best fleet technicians I have met are fully engaged in the systems of operations and are always looking for more technical training. This transition from fossil fuels to renewable forms of energy is an exciting time and fleets will need thousands of EV-trained technicians. Volunteer to be the EV tech and your future will be secure.

Maintenance of any EV by a lower-level technician is problematic unless a well-trained tech is in the next bay mentoring the new general maintenance tech. What about a cabin air filter on a heat pump EV where the high cables are inches away under the dash? There are many examples on an EV that can be a problem for an inexperienced technician. They may just be unaware of what is nearby. (Remember “you don’t know what you don’t know,” and that can be dangerous!) The OEMs have their recommended service intervals. In most areas of the country (California can be an exception) a dealer or independent shop can recommend more maintenance if they see the need or believe the owner would benefit in the long run to do more PM than the OEMs recommended. In California you may have to present some proof that the extra PM is needed — not just your own experience. Training is still vitally important from just a safety aspect when performing preventive maintenance on EVs.

12-Volt Battery

The 12-volt battery is really important. Many 12-volt batteries are located in the hatch or trunk area. Test it! Look up the specifications and make sure it is OK. When a customer relies on their EV for work and other activities that require “on time” performance — like their job — being late is not an option. The 12-volt battery really is the most critical part of the EV (just like any vehicle) if you want it to start. It is often overlooked. Did you know that Tesla will monitor the 12-volt battery and report to the driver before it fails that it needs replacement? Did you know Tesla recently switched from lead acid chemistry to lithium (16-volt)? In either case, if the 12-volt battery (we use that number for simplicity) is getting low on a charge, before it is too late, the high voltage battery is connected to the DC-DC converter and in turn recharges the 12-volt battery. The car is programmed to do that, even when it is parked. By having that function, the EV will always start. Ford has added that feature. Keep in mind that the HV system can go live at any time if the 12-volt battery needs replacement.

Bleeding multiple cooling systems

Air will get trapped in any liquid cooling system and the thing to remember is that many of the cooling channels are horizontal, not vertical, as in most ICE systems. Once you have flushed or added coolant and bled the cooling system, drive carefully in an area away from traffic and rock the steering wheel side to side. Be careful as you do this. The idea is to get the air moving horizontally and that will help get the last of the air back into the coolant reservoir. You may need to add some coolant after the road test. If you do, you will know that the road test was worth your time. These systems often have bleeder screw(s) somewhere. They can be at the top of the inverter or at the radiator.

Tech Tips

The General Motors Bolt EV locked the radiator cap by allowing the outer portion of the radiator cap to just turn in a circle without doing anything. To remove the cap, you need to insert a small flat screw driver into a slot that locks the cap to the housing. GM is trying to keep those without the skill away from the fluids.

When the Nissan Leaf came out in M/Y 2011, code “P31DE” would set to tell you to perform a PM service. That service was to remove the HV battery pack and replace the HV “Junction Box”. No easy task and an experienced technician will be needed to do this job. In the battery junction box are the HV contactors that connect and disconnect the HV battery when starting and shutting down the car. Nissan keeps track of how many times the contactors have switched on and off “due to high current” as stated in their service information. It is unclear exactly why and when this will happen. If you see that code “P31DE” now you know why it was created.

When you follow the PM for the Mitsubishi i-MiEV, you will notice a service that will have you clean the J1172 EVSE receptacle. We have seen no other OEM require this, but it is easy, so why not do it. Use some contact cleaner and “Q” tips to clean the pins.


The key word preventive describes a service for well-trained techs to oversee or perform. When a vehicle is on a lift you are checking for safety problems like loose steering and suspension parts, fluid leaks, worn tires and more. If allowed to go unnoticed, problems could cause an accident, injury or death. Other items need periodic replacement, like wiper blades, cabin air filters, washer solvent and such. All EVs will wear out tires and brakes (eventually). The more you know what to look for, measure, and feel, the more thorough you can be. Preventive maintenance is important and necessary.

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