Tesla Model S GPS antenna testing

Testing the GPS antenna of a Tesla Model S

Some background about this project: 

Two months ago after a software upgrade the navigation of my 2015 Tesla Model S with upgraded  Media Control Unit (MCU2 Intel Atom) got stuck. The arrow of the navigation does not move anymore and is stuck at the position of my home address. The navigation never had issues before. The other functionalities of the MCU are all fine and working as expected.

To fix the navigation issue I tried the following resets after removing my USB stick from the system:

• Soft reset by pressing the both scroll wheels on the steering wheel
• Full soft reboot by powering off from the menu
• Hard reset by disconnecting the 12V battery and first responder loop

None of the resets solved the issue.

Tesla service next diagnosed the issue to be caused by a defective factory GPS antenna. That I found rather strange because it never had issues and when it dies suddenly why would that happen at my home address and not somewhere while driving.

Since the antenna is rather cheap (50€) I decided to have it replaced anyway. Tesla Service then however informed me that since the antenna is mounted under the glass of the rear window (a stupid design decision) they would have to cut the glass out. Since there is then a big chance that this breaks the glass there was and additional charge in that case of more than 1000€.

To me this was unacceptable I told Tesla Service that I will buy the GPS antenna (1004794-00-B) over-the-counter and install it myself against the rear window somewhere.

Connecting the GPS antenna in the rear trunk is super easy, takes about 5 minutes. The connector for the factory GPS antenna is stuffed up behind the rubber boot on the driver side of the rear lift gate. Just fish it out. The connector has a clip on top that needs to be pressed to release it. After disconnecting it, connect the new GPS antenna.

Connecting the new GPS antenna that way did not solve the issue. 

Assuming the new GPS antenna is not also defective the next thing would be to check the cable between the MCU2 and the GPS antenna. To do this I bought a Fakra-C extension cable for GPS and connected it with the new GPS antenna to the MCU2 after detaching the original cable.

The GPS antenna cable connector at the backside of the MCU is fairly easily accessible by removing a big single L-shaped trimpiece (above the glove box). The connector for the GPS antenna is the first connector (blue female Fakra-C) that can be seen on the back of the MCU from the passenger side footwell. You need to crawl in there lying on your back and not have big hands :-) 

The connector has a clip on top that needs to be pressed to release it.

Connecting the new GPS antenna using the extension cable to MCU and positioning it on the dashboard did also not solve the issue.

It was time to contact Tesla Service and inform them that their diagnosis of a defective antenna seems to be incorrect. This however they still found difficult to believe and I was told that without cutting out the rear glass they could not make sure that the antenna is positioned correctly.

After recovering from this remark I decided to test the GPS antennas and cables myself. For the tests I will be using a cheap (but excellent) mini  GPS satellite module using the NEO-6M module from u-blox. 

The GPS satellite module has a TTL serial port that is connected using a FTDI232 USB to TTL serial port adapter.

The test setup uses a MS-Windows laptop with the free u-blox GNSS evaluation software utility called u-center to check the functionality of the GPS receiver and the antenna. I will be testing the new over-the-counter GPS antenna positioned on the dashboard (A) and the factory installed GPS antenna under the glass of the rear window (B).

A. Test setup with the over-the-counter GPS antenna on the dashboard 

The antenna is placed under the front windscreen of the car. This experiment was done to proof that the antenna is working and also is functional when not placed under the glass in the driver side top corner of the rear windscreen. 

Result: The GPS receiver and new GPS antenna work as expected!

B. Test setup with the factory GPS antenna mounted under the glass of the rear windscreen

This test was done to proof that the factory GPS antenne and cable is working and functional. The GPS antenna cable connector at the backside of the MCU is fairly easily accessible by removing a big single L-shaped trim piece (above the glove box). The connector for the GPS antenna is the first connector (blue female Fakra-C) that can be seen on the back of the MCU from the passenger side footwell. The connector has a clip on top that needs to be pressed to release.

Result: The GPS receiver and factory GPS antenna work as expected!

Conclusions at this stage

At this stage it has to be concluded that the problem seems to caused by the MCU itself. Either hardware or software. My guess is that the GPS module used by the MCU is probably defective or in a state that it does not operate anymore. 

The navigation module for MCU2 based cars seems to be a LEA-6R (or NEO-8L?) from u-blox. The module can be connected using serial interface, SPI or USB. Most likely Tesla uses the USB interface since in newer Tesla cars a lot of issues are reported with respect to the navigation arrow being stuck in one position due to connected external USB devices causing the issue. In most cases after disconnecting the problematic external USB device (often USB hubs) the problem is solved. For this reason to be sure I've removed my USB stick with MP3 music files.

The next thing that I wanted to try is to replace the 16GB micro SD card (1014633-S3-C) used by the MCU. Perhaps this card is also connected to the USB bus and could maybe be corrupted causing a similar issue in my case.

If this does not solve the issue I think the u-blox module needs to be replaced. I believe it is together with the LTE connectivity module mounted on a dedicated board PCBA (1054968-02-C) costing around 100€ inside the MCU that can be swapped (see picture below). No idea if Tesla Service is capable of repairing a MCU at board level or only swaps complete MCUs. This again would be unacceptable..too expensive for only a navigation issue and everything else working correctly.

Connectivity board with u-blox module (bottom-left)

Update after further investigations 

The replacement of the 16GB micro SD card (1014633-S3-C) used by the MCU did not solve the issue. The next option would be to replace the LTE connectivity board with the u-blox navigation module. After asking Tesla Service for a quotation to replace the connectivity board they informed me that the LTE connectivity board part number I suggested (PCBA 1054968-02-C) is incorrect for my MCU. The correct part number according to Tesla Service should be (PCBA 1054968-01-C). This however is not the LTE connectivity board but its predecessor for 3G connectivity used in the original MCU that came with the car before the MCU2 upgrade.

After informing Tesla Service that this can not be correct they changed the invoice to include the LTE connectivity board I suggested. When I suggested to try replacing this board I also asked Tesla Service to verify that this connectivity board is indeed used in the MCU2. Because convincing Tesla Service of the mistake with the 3G connectivity board was not that easy I now decided to check myself to be 100% sure.

For some reason unknown to me the Tesla parts catalogue does not seem to contain information about the part list of the MCU2 that was used to upgrade older Model S and X cars. Tesla Service confirmed this when I started asking questions about it.

On eBay I did find some pictures of the internals of the MCU2 that show that the MCU2 is a totally different hardware design. One of the main differences is that the connectivity board is now mounted on the other side of the main board and it also no longer contains the u-blox navigation module. The u-blox navigation module is now soldered on the main board (PCB). 

I also noticed that some versions of the MCU2 do not have the u-blox module soldered and also do not have the connector for the GPS antenna  (blue female Fakra-C) soldered on the back of the main board. This version of the MCU2 seems to be for cars with the newer Autopilot versions. These cars have the GPS antenna connected to the Autopilot hardware module instead of the MCU.

Below are some photographs of the MCU2 hardware versions.

                                    MCU2 main board with u-blox module soldered (yellow highlight)

                                      MCU2 main board without u-blox module soldered

MCU2 back view with GPS blue antenna connector (first from the left) soldered

MCU2 back view without GPS blue antenna connector (first from the left) soldered

Above the middle grey connector that can be seen on the back of the MCU2 there is connector that is provided by the connectivity board of the MCU2 (see photograph below).

                              Connectivity board of the MCU2 (in the middle of the board)

The connectivity board of the MCU2 contains a big module (in white): a Telit LE940B6-NA for LTE (4G) connectivity.

To fix my navigation issue (considering it to be a hardware issue) these are now the remaining options:

1. Replacing the u-blox module on the main board of the MCU2. Probably not an option for Tesla Service.
2. Replacing the main board of the MCU2. Not sure if it is available as a serviceable part by Tesla Service.
3. Replacing the entire MCU2. A very expensive solution for the problem.
4. Replacing the car (just kidding).
5. Do nothing and live with it

To be continued?