Although you may already provide service on Teslas, this article could reveal information you may not be completely aware of. Since Teslas fall into the “Software Defined Vehicle” (SDV) category, changes are continuously added to not only enhance the driver experience, correct for bugs and other issues, but are also rolling out changes to enhance the service technician’s experience as well. I now own two Tesla vehicles and over the past five-plus years I have witnessed many interesting changes that have allowed for better diagnostics and a way for those interested in learning more about how these machines work to learn more through the highly informational graphics displayed on the center screen when in service mode, and the theory of operation data now made available within service information via subscription. A quick example of this is shown in Figure 1 displaying the live thermodynamic heat-pump data values on a Tesla Model Y.
In this article, you will find plenty of graphics, explanations, and several use cases that I believe you will find to be highly informative. We will also cover how one can now access the vehicle remotely to triage and analyze vehicle problems before the vehicle arrives for service. I will also share an interesting case study where I was able to support a colleague, with a shop in Central California, in addressing a high-voltage battery problem on a 12-year-old Model S.
The role of automotive service technicians is evolving. With the advanced tools built into vehicles, such as those found on Teslas, you can experience the vehicles of the future today. The aftermarket service of Tesla vehicles poses unique challenges and opportunities, requiring a specialized understanding of Tesla's proprietary systems such as Toolbox, Garage, Periscope, and service information. This article aims to provide professional automotive service technicians with a detailed overview of Tesla Service, highlighting recent access developments and how they can leverage Tesla’s service tools.
Service Mode & Service Mode Plus
Going back about four to five years ago the aftermarket had no access to service mode or service mode plus unless you were a certified collision center. Today anyone can engage service mode through a couple of key presses on the screen. When accessing the software page and long pressing on the model's name of the vehicle for approximately five seconds, a password entry box should appear, and entering the word service will allow you to engage in service mode. A disclaimer screen will appear letting you know that you could get yourself in trouble if you don't know what you are doing. So, you should be cautious until you are highly fluent with Tesla vehicles.
On this first page (Figure 2), the first thing that I recommend doing is looking at the service alerts. This provides a list of alerts and warnings that may be useful when addressing vehicle problems or complaints. But beware, researching this information should be carried out before engaging in any level of diagnostics because I have seen several alerts and warnings for items that are known issues and that may be corrected sometime down the road through software updates.
Additionally, the alerts shown either on the in-car display or in Toolbox may have an additional payload of cracked data that might be useful to the service technician (Figure 3).
For example, APP_w303_imuIrational on my 2018 model 3 equipped with a hardware 3 car computer indicates that there is a rationality error between the accelerometer or IMU (Inertial Measurement Unit) located in the restraints control module and the IMU located inside of the car computer a.k.a. Autopilot computer. This is one example of a known issue that is supposed to be corrected with future software updates according to what Tesla shared with me during a service visit to address this alert. However, I have discovered something unusual on this vehicle that may be related to this IMU anomaly which I will share more about later in this article.
There is another known false positive and that has to do with an indicated voltage drop. VCFRONT_a059_inputResistanceHigh. Reviewing service documents on the Tesla service information website can sometimes reveal these known issues and sometimes a Google search may reveal actual vehicle owner experiences and what Tesla service advised on such anomalies. Today’s technicians need to be highly resourceful and in doing so may save valuable time and effort. However, there are cases where you will not be able to look up certain fault codes unless you are using Tesla's Toolbox 3.0 software where a lot of useful diagnostic information can be found.
Tesla Toolbox 3.0 Software
Tesla Toolbox is a diagnostic and repair software offered by Tesla to access additional service information within the vehicle and from within the online application. The software runs in a web browser (preferably Chrome) where the computer is connected to an Ethernet diagnostic port located under the dash near the drivers kick panel. Service information will provide settings that will need to be set up with your network connection on your laptop or computer and specific settings that the browser needs to have. Essentially, you'll need to assign a specific IP address to your network interface card and turn off all the security-related settings within the browser. Some of the earlier cars require specific connectors however for 2022 and later cars, the standard RJ45 cable connection is all you need to connect.
When you connect the vehicle with Toolbox, the vehicle is automatically placed into Service Mode Plus. Service Mode Plus provides additional diagnostic access through the display screen found in the vehicle so let's review a few of those differences.
High voltage battery page
Additionally, there are a couple of relearns for the calculated ampere-hour charge and state of charge levels. You'll need to review service information and obtain additional training to understand why one would need to execute these changes. And later in this article, I will share a case study where we performed these operations and were able to successfully enable a vehicle that had learned incorrect cell balancing values.
Here's a note about resetting the high voltage battery management system calculated ampere-hour capacity.
“Resetting the calculated ampere-hour capacity may cause the vehicle to prematurely enter graceful power-off mode at a displayed percentage or mileage above zero. It is important to inform the customer not to drive the vehicle below the 20 percent displayed range for the next eight weeks following a calculated ampere-hour capacity reset. This routine resets all the high voltage battery brick calculated amp hour capacities to the nominal/default values. During normal operation, the high voltage battery management system calculates brick-calculated amp hour capacities over multiple charge/discharge cycles. In the event of a large, accumulated error, this routine can reset the calculated amp-hour capacities based solely on the nominal/default brick calculated ampere-hour capacity values to improve the high voltage battery management system full pack energy prediction.”
On the low voltage page, you will have access to a can bus diagnostic panel which is not available in regular service mode. As you can see in the attached image, this gives you a visual representation of three of the main can busses on the vehicle and the various module states (Figure 5). If one of the modules has a problem, it will be indicated on the screen. However please be aware that you need to make sure that various drive rails (power supplies) are enabled so that these modules can talk. These visuals indeed can be extremely helpful when tasked with communication problems.
If you’d like to learn more about entering service mode and some of the ins and outs, here’s a link to a video I live-streamed in early 2024 that walks through Service Mode: youtu.be/nRW7evDC7O0?si=YkXfyf08vpthoiwi
Tesla Garage
Tesla Garage (Figure 6) is accessible from within your active Toolbox subscription and provides you with a way to remotely connect to a vehicle and retrieve more information about the vehicle. This can be extremely helpful in not only looking at current vehicle data but can offer up a look at high-resolution data from the past.
To obtain connection permission, you’ll need to use the Owner Authorization Request function. After making a Garage connection, then it would be wise to go into the CAN Explorer (Periscope) and request data logs from the past when the client was reporting vehicle symptoms. Once you do this, then when you are researching vehicle problems and viewing articles, it is possible that you might be presented with a notice like what is shown in Figure 7.
If you select the “View Plots” link, you’ll automatically load up Periscope which is Tesla’s data viewer allowing service personnel to research vehicle problems. Tesla Periscope is a newer addition to the Toolbox suite of service tools, and it’s a powerful tool as you’ll see demonstrated later in this article.
Sandbox
Maintenance services
Tesla and other BEV’s will require maintenance. Here is a list of services we carry out in our facility.
- Alignment and tires – Tires for EVs have more demand due to vehicle weight and torque. Tires should be rotated every 5-6,000 miles. Wheel alignment checks can be done via software within service mode, but I have found many of these vehicles leaving the factory with wheel alignments that are not set up for optimum tire life. HVAC – The A/C system is an integral part of the EV systems and on pretty much all EVs. Therefore there are maintenance and inspections that should be performed on Tesla’s. Every five years Tesla states that the desiccant bag shall be replaced (Figure 9)
which of course will require an evacuation and recharge of the system.
Be sure to check service information for the appropriate tools and equipment needed to remove and install the desiccant bag and filter. This is also a suitable time to make sure that there is the proper amount of oil within the system which can be checked using an appropriately prepared sight glass as shown in Figure 10.
- Brake Systems – The brakes rarely get used on an EV that is driven in a manner that is most efficient, but the braking system still must be able to stop the vehicle. Periodic inspections of the brake pads and rotors should be performed. Additionally, periodic maintenance on the brake caliper sliders along with brake fluid replacement should be performed as well. Check service information for more info.
- General inspections – Teslas use a lot of aero close-out panels which should be removed periodically for proper inspections. Looking for any anomalies such as hose or harness routing, evidence of critter exploration, drivetrain mounts, and heat exchanger airflow problems that can occur from the accumulation of debris between the condenser and radiators. Additionally, since BEVs weigh 20-30 percent more than their ICE counterparts, suspension wear and tear will likely present many service opportunities.
Case study – Model S battery issue
I received a text from a colleague about a 2012 Model S with 174k that arrived at his shop with a client complaint of a warning message on the display stating that there was a problem with the HV battery and the fact that the client was unable to charge the battery above 30 percent. After gaining authorization from the client to remote into the vehicle, we retrieved an Urgent Alert BMS_u018_SOC. Looking this up in Tesla Toolbox I came across Article 7763300 which had the following statements:
“In certain scenarios, a customer-visible High Voltage (HV) battery State of Charge (SOC) imbalance alert sets due to a condition unrelated to the HV battery
bricks.
In these situations, it is prudent not to simply replace the HV battery pack without further diagnosis to confirm an SOC imbalance exists: in some cases, simply updating the vehicle firmware or running an Onboard Diagnostic Interface (ODIN) routine might
resolve the issue.”
The document listed several steps to follow which we did and were able to get the vehicle to charge well past 80 percent. The cell balancing deltas went from approximately 422mv to 40mv over the course of a few days of discharging and recharging the battery after performing the resets outlined in the service document. Here are the data valves we collected near the end of one of the final charge cycles:
- Voltage: 385.3 V
- Battery Min Temp: 27 °C
- Max Temp: 28 °C
- Min Brick V: 4 V
- Max Brick V: 4 V
- SOC Min Unscaled: 81.8 percent
- Max Unscaled: 86.2 percent
- CAC Min: 239 Ah
- CAC Max: 239 Ah
- CAC Average: 239 Ah
Looking back at the data logs from the vehicle during our discharge > recharge routines, I was able to observe the cell min and max values and their progression over time (Figure 11).
This vehicle was recently purchased through a used car dealer and with no service history and over 174k miles on the clock it might need a new traction battery in the future, but for now the client is getting effective use out of the vehicle. The shop will continue working with the client so we can monitor battery performance.
Case study – Model 3 – Inertial measurement unit
Although the following issue has yet to be resolved, I strongly believe that this scenario will provide technicians with insight into what Tesla has to offer regarding diagnostics.
The vehicle is a 2018 Model 3 with approximately 80,000 miles. This vehicle is equipped with the FSD (Full Self Drive) car computer hardware version 3.0 which is Tesla’s first internally developed hardware to support their self-driving efforts. My vehicle did not come equipped with this module, but Tesla made a retrofit option available back around 2021, so I opted into it. I have been studying the full self-drive capabilities and can attest that I have seen a remarkable evolution in vehicle capabilities taking place.
About a year or so ago I started noticing some strange vehicle behavior especially when the vehicle was operating in self-drive. I was interested in seeing if there was any vehicle data that could help explain what was happening. I also began seeing a recurring warning titled APP_w303_imuIrational. Now when you look at these alerts and warnings in the Toolbox Periscope application, the alerts and warnings will typically carry a payload of data that can be analyzed, but beware, the alerts and warnings are triggered by the clear event and not at the time the fault was triggered.
When researching the article covering this issue, the warning is explained as follows:
“The Autopilot electronic control unit (ECU) internal inertial measurement unit (IMU) is irrational compared to the IMU from the Electronic Stability Program (ESP) or Restraint Control Module (RCM). This may occur due to an internal condition affecting the Autopilot board or may set temporarily due to aggressive driving (high lateral and longitudinal acceleration).”
I only recently associated the temperature relationship due to the next scenario I began to unfold starting this summer. The data demonstrates that the alarm begins going off each day around noon when the ambient temperature rises to approximately 34 degrees Celsius (Figure 13).
As I began to dig further, I decided to have a look at the Sentry video recordings stored in the user-accessible USB drive associated with these events. I believe I found additional evidence pointing back to the autopilot’s IMU as being the potential cause. When you look at the folders created for these sentry events, you’ll find a JSON file that has metadata containing the timestamp, location, reason, and which camera detected the condition. In this first example, the sentry_panic_accel value appears to indicate .9 g’s of longitudinal acceleration were indicated by the IMU.
{
"timestamp":"2024-08-14T15:31:33",
"city":"Claremont",
"est_lat":"34.0932",
"est_lon":"-117.718",
"reason":"sentry_panic_accel_0.903371",
"camera":"0"
}
For comparison, here’s what the JSON file stores for another event:
{
"timestamp":"2024-08-24T18:48:45",
"city":"City Name",
"est_lat":"34.000",
"est_lon":"-117.000",
"reason":"sentry_aware_object_detection",
"camera":"0"
}
So, to close this out for now, I believe that the IMU on the autopilot board is the cause of this anomaly. Soon I plan to work towards a resolution and to share this journey in full when able. If you have any insight you’d like to share, please do.
I hope you found this article helpful and informative and if you’d like to see more Tesla coverage, please let us know as there is a lot more we can discuss. If you have any questions or comments, please leave them here or feel free to reach out.
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