Performing a ‘safe down’ procedure on electric cars


By Craig Van Batenburg

What have the automakers done directly or indirectly to help protect technicians working on hybrid and electric vehicles? Electric and hybrid vehicles have a lot of safety built into them, but as with any technology, play it safe! Read up on these cars before moving past a warning label.

For the safety of passengers, first responders and technicians, once an airbag is deployed, the high-voltage (HV) system on such vehicles is shut down, with one exception: the Ford Escape HEV (and its clones, the Mercury Mariner HEV and Mazda Tribute HEV). The first Ford hybrid system used an “inertia switch.” Once this switch sensed an impact that Ford calculated was serious enough to compromise the HV battery pack and related systems, it would send a signal to the HV battery engine control unit and the battery pack would be turned off. At the same time, the HV capacitors would discharge. Once any high-voltage storage component was either turned off (i.e., the HV battery is disconnected but still has high voltage in it) or discharged (the HV capacitors are a good example), the technician has a much safer environment to work with in.

So what do you need to know about these HV vehicles? First, you need to know how to turn off the vehicle, if it does not have a metal key. Second, you need to know that orange cables mean high voltage. Third, you need to know how to de-power and test the HV system for zero volts. If you are not near the orange cables or any high voltage part, then you may be fine, but a thorough understanding of the entire vehicle you are working on is the only way to be sure you are safe. Proper training will get you started in the safe handling of the HV systems.

Once you have determined that you will be near an orange cable or junction, you will need to de-power the capacitors and disconnect the HV battery back. The good news is that by just turning the car off and removing the key, that action is done. Or was it? The HV battery and the HV capacitors can really hurt you as they store energy. More on this later.

If you see bright blue cables under the hood of a GM vehicle, you are looking at a potential of 36- to 42-volts or intermediate voltage (Itv). These are “micro hybrids” and are well below the level of danger. But 48-volt systems from many OEMs have found their way into hybrid motor vehicles today. Never take chances, and treat any electric or hybrid vehicle as if it is a high-voltage system until you know for sure it is not HV but Itv. 

At some point you will have to remove or disconnect a high-voltage part. Many repair or preventative maintenance jobs — like replacing a headlight, doing an oil change or fixing a flat – do not require a “safe down,” because these parts of the car are not high voltage.

But in any case, to be safe, make sure you turn off the car. These vehicles are relatively silent in “ready to drive” mode. Some hybrid models can be in ready-to-drive mode with the hood open and the internal combustion engine off. This can cause confusion during an oil change as the engine will restart when the HV battery is drawn down to a low state-of-charge by the use of 12-volt accessories. This was explained more fully in a DC-DC converter article in an earlier edition of this publication. Make sure the dash is dark and the car is off before working under the hood, doing a brake job, or working with the high-voltage system.

When do you need to “safe down” an EMV with a high voltage (HV) system? When you are done diagnosing the problem and it is time to remove a HV part, when you are unsure about your exposure to HV, when the OEM instructions tell you to, or any other time you know you should.       

Here is a simple “safe Down” generic procedure for a high-voltage system (note that a fuel cell vehicle has more steps):

1. Get all of your scan tool data first.

2. Shut off the car and remove the key.

3. Put the key(s) away (out-of-sight or locked up).

4. If keyless, try to start it again. If it starts, there is another keyless remote in the car. Find it, or make sure you disconnect the 12-volt battery.

5. Make sure you have the correct 12-volt battery disconnected. Some HEVs have two 12-volt batteries near each other.

6. Wear your Class 0 1,000-volt currently-certified HV gloves, and remove the service plug, turn off the switch (or pray, because some European HEV did not include a “service plug” on their first HV vehicles). Leather protectors over your HV rubber gloves is always the best idea. 

7. Hide or lock up the plug. Prevent the switch (same EMVs have a switch) from accidentally turning on. 

8. Remove the cover to access the cables or metal tabs that lead to the HV battery. This is model-specific. There are technician guides that have OEM-specific information. Test to be sure the HV battery is off and isolated from the rest of the HV system.

9. Using OEM service information, locate the capacitors and test for HV. The normal design of the EMV will automatically discharge the capacitors at each shut down. Be sure they are not charged up. 

10. When using your CAT III meter, keep a small AA battery with you. There is a three-part procedure for making sure your meter works. Test the AA battery first.  Does your meter read 1.5 volts? If yes, test for HV at whatever location you need to test at. Did you get a reading of zero volt? Then check the AA battery again. Did you get 1.5 volts? 

11. Wear your safety gloves until you know it is safe. Always wear your HV safety gloves when handling a HV battery pack as even a one percent state-of-charge can be lethal.

12. Re-test for HV if at any point you have left the car and it was out of your view or control.

Although a lot of redundant safety devices are built into EMVs, the potential is there for a technician to be hurt or killed. Most technicians are typically trained for one week on high-voltage systems by the OEMs before they are allowed to work on them. The safety issues are real, so be safe. My company for close to two decades has offered books, webinars and classes on servicing hybrid and electric vehicles. More information can be found at  •

Craig Van Batenburg is a former repair shop owner who is the CEO of Automotive Career Development Center (, which offers training and consulting related to electric and hybrid vehicles; he can be reached at