Electric Vehicle Repair: 12V Battery and TPMS

Electric Vehicle Repair: 12V Battery and TPMS

What is the proper way to jumpstart an EV? And why are the tires on a Tesla one of the first things that will need to be replaced?

Here’s a real-world scenario: A customer brings an EV into your shop for service, and it’s been there for quite a while because the parts are on backorder. After a few weeks, you get in the vehicle to move it out of your way, and the ignition won’t turn on. It’s acting like the battery is dead, so what do you do now?

Chances are that the low-voltage (LV) or 12-volt (12V) battery inside that EV has gone dead. In most cases, the LV battery is not charged while the high-voltage (HV) battery is plugged into the wall charger. So, even if your shop is outfitted with an HV wall charger, the LV battery could still go dead if it’s left alone long enough.

This scenario can present a few unique challenges to technicians or shop owners. The first question we need to ask ourselves is, “Can I jump this EV with another car?” I would advise against this idea. It’s much safer to have a dedicated battery jumper, preferably one with some electronic assist to protect the system from surges, inverse polarity, etc. Compact battery jump packs are available and are really handy for all kinds of situations.

Now you need to find the LV battery, and it could be anywhere in the vehicle. This location, of course, will vary from one EV to the next, but the most common locations would likely be under the hood or in the trunk. But, herein lies another challenge: Some EVs, specifically Teslas, have electronic door poppers that release the trunk and the hood, a.k.a. the front trunk or “frunk.” So, it sort of turns into a “chicken before the egg” situation. How can you open the hood to get to the LV battery and jump it if there’s no 12V power to actually open the hood?

Fear not, because Tesla thought this one out. There is a pair of wires located just behind the front tow hook cover in the front bumper cover. With a 12V battery jump pack on hand, press firmly on the top right perimeter of the tow hook cover until it pivots inward, then gently pull the raised section out toward you. Pull the two wires out of the tow eye opening and connect them to the jump pack: red positive to red positive, black negative to black negative.

Be aware that these wires are not a charging point for the LV battery. Applying 12V power to these wires will only pop the hood release, but now you can gain access to the LV battery inside. Open the hood and remove the trim panel that covers the LV battery. Locate the positive charge/jump post and connect a suitable battery charger or jump pack to it. Attach the negative cable from the charger/jump pack to the beam in front of the LV battery. You should now be able to charge or jump the LV battery and power on the ignition.

Tesla TPMS

Some of the first items to be replaced on any Tesla model are the tires. This is due to tire wear from the instant torque of the electric motor. When replacing the tires, you will have to service the tire pressure monitoring system (TPMS) sensors. Tesla has used Baolong (from 2012 to 2014), Continental (from 2014 to 2020) and a proprietary sensor that uses Bluetooth. For 2021, the Model Y started to use a sensor that communicates using Bluetooth protocols. Not much is known about the new system except that the sensors are currently available only through Tesla.

The Baolong TPMS system will not display the pressures on the center display. However, the Continental and Bluetooth systems will display the pressures for the driver. Tesla offers a retrofit kit to convert the Baolong system to a Continental system. The procedure involves replacing a module on the vehicle. Baolong sensors are available on the market, and aftermarket replacements can be programmed for the car.

Like many TPMS systems, the Tesla TPMS system has a built-in feature that automatically detects a new set of wheel sensors. The TPMS sensors can be reset via the vehicle’s touchscreen. The reset function is only possible when the vehicle is on.

Before starting, set the tires to the correct cold tire inflation pressure according to the door placard and tire size. Before servicing the tires, make sure the system is functioning.

To get started, turn the touchscreen on. Go to controls, settings, service and reset, tire pressure monitor and reset sensors. Reset the sensors based on the wheel size.

If a tire pressure warning displays, exit the vehicle, close the rear trunk and all the doors, wait for the touchscreen to go black, re-enter the car, and ensure that the correct wheel size is selected before touching reset. Touch reset, and then touch OK.

Press and hold one of the scroll wheels and select “Car Status” to see an overview of the TPMS information. When the sensors are unknown, all the values will be shown as “- -.” Ensure that the vehicle is stationary for at least 20 minutes before continuing to the next step.

Perform a road test. Auto learning will start when the vehicle exceeds 25 mph. When auto-learning completes, the tire pressure information displays for all wheels and clears any TPMS faults. Note: Auto learning can take up to 20 minutes during a test drive.

Try this procedure again if “Tire Pressure System Needs Service” displays after performing auto-learning. If the warning still persists after five minutes of driving at 25 mph, further diagnostics might be required. This can include using a TPMS tool to verify the operation of the sensor.

Most Tesla models use service kits that have a clamp-on metal stem. A new service kit should be installed every time the tire is removed from the rim. The valve stem’s nut is a one-time-use item. Most kits are available in two finishes for silver and black rims.

There are a wide variety of programmable 433-megahertz sensors for Tesla models. There are also direct replacement
options. Starting in 2020, Tesla started using Bluetooth protocols for the TPMS sensors. These sensors work the same way as conventional sensors, but they will require a TPMS tool with the correct software to check the condition of the sensor.

Resetting and programming TPMS sensors for a Tesla is a lot like any other vehicle, but the challenge is still the same: keeping the light out.

You May Also Like

Detroit: The Heart of the Auto Industry

The city is back and alive, and cars are at the heart of it. All of us here at BodyShop Business will be there July 28-Aug. 2 for NACE, and we hope you will be too.

Many will argue that the first automotive concentration was in Indianapolis, and to a certain extent that’s true. But few can argue the role Detroit played in the overall transformation and centralization of the automotive industry. I’m departing from my usual format of writing about cool shops to talk about something that I’m passionate about and believe you should be passionate about, too.

Buying Tips: Frame Machines/Benches

We talked to several manufacturers to find out what collision repairers should be looking for when shopping for a new frame machine or bench.

Crashrepairinfo.com Is Here

Launched by the OE Roundtable, crashrepairinfo.com educates consumers on technical information, various types of parts, repair rights and more.

Life in the Fast Lane

The collision center at Gullo Ford discovered that creating a “fast lane” for minor collision repairs was the key to improving its cycle time.

Mechanical Repairs May Help Fix Your Bottom Line

Detailed mechanical information can eliminate the need for body shops to outsource certain jobs, increasing their profits and giving them more control over their repair schedules.

Other Posts

Honda Starts Production on 2025 Honda CR-V Fuel Cell EV

The all-new CR-V e:FCEV is the first production hydrogen FCEV in the U.S. to combine an all-new U.S.-made fuel cell system with plug-in EV charging capability.

Virginia Will Not Adopt California’s ICE Ban

SEMA applauds Virginia Governor Glenn Youngkin’s action to reverse the state’s EV mandates.

AAA Survey Says EV Hype Might Be Over

Only 18% of U.S. adults say they would be “very likely” or “likely” to buy a new or used EV.

Report: Decrease in Used EV Prices Coincides with Increase in Total Loss Claims

Mitchell trends report indicates EV total loss rates were 9.93% and 7.48% in the U.S. and Canada, an increase of approximately 8% from Q4 2023 and 30% from Q3 2023 in both regions.