One of the very common error messages in Mazda cars is the “In-vehicle network malfunction” message. It attacks Mazda 3 and CX-30 owners mainly, but other modern Mazda models are also prone to the issue.
This message is most likely there on the dash and/or on the infotainment screen because of the TCU (Telematics Communication Unit) problem. It may be broken, have a glitch in its software, or its battery may be low.
Also, there are other reasons like GPS-antenna problems or connectivity issues. Also, this problem is pretty hard to locate, so even dealers very often make wild guesses about its reasons.
Please note, there is the TSB for this issue – SA-029/20. It will work in dealerships, and they often don’t know about that, so remind them.
What are the possible problems?
If you see the “In-vehicle network malfunction” message, it means that your Mazda has lost communication with the cloud or between electronic units.
The most common culprit is the TCU. But it’s not the transmission control unit as you might have thought, this is the Telematics Communication Unit. The thing that controls the GPS and also cloud updates for your Mazda.
Here are the most common problems:
1) TCU has issues with its software
In this case, you will need to update this software. The easiest way is to go to the dealer and tell them to do so. But it’s not for free. You can do this on your own.
You will need the new software update files for the TCU and CMU (Connectivity Master Unit) for your vehicle, and a flash card formatted in FAT32. The process is pretty intuitive – just insert the flash card into any USB port and the vehicle will tell you what to do.
The hardest thing is to get the correct file. You will be able to find them on forums and in independent shops. But this is pretty risky, I should say.
2) The TCU battery is dead
Yes, the Telematics Communication Unit has its own battery that isn’t charged or backed up by anything else. It proves to be dead after about 3-4 years of use but it depends on the weather in your area.
So, this is the 9V lithium battery and the dealer will probably tell you that you need it only OEM for something like $90. That’s not true – any 9V lithium battery will do just fine.
The TCU is located behind the glovebox in the Mazda 3 and CX-30. For other models, please check your manual. Opening the unit and changing the battery is pretty easy.
3) Communication and wiring problem
There are several things that may be disconnected. Potentially, you can find them just by looking at the fault code. But for this, you will need an original Mazda scanner. A simple OBD2 scanner will wrongly show something like P0602 which is irrelevant, in this case.
So, here are the modules that can lose connection and lead to the “In-vehicle network malfunction” message:
- GPS antenna connection to the TCU – it’s known to be problematic;
- cable connection between TCU and CMU – also a very common issue;
- BCM (body control module) connections – they can also rarely cause this problem.
Unfortunately, to check all the connections, you will need some knowledge and tools. I advise you to go to the dealer and let the mechanic do this job for you.
4) Temporary glitch
It’s completely common for a modern Mazda vehicle to develop a software glitch. A modern vehicle may have up to 30 electronic control units. They are essentially little computers with their software and possible glitches. If you experience the problem on the CX-5, this is probably your option.
So, it’s not uncommon at all for them to have some miscommunication. If this is the problem, you will need to reset the modules. How can you do that? I will tell you in the next section.
What can you do to solve the problem?
Now that you know the possible reasons for the message, you may want to know what exactly you can do to solve the problem. And this is not as easy as you may hope.
I will start with absolutely free and easy methods and move on to the least wanted options.
1) Disconnect the 12V battery for a while
If this is a glitch in the communication systems between modules, you can try to solve it by disconnecting the battery for 5-7 minutes. Be careful – disconnect the negative terminal first.
After you reconnect the battery, start the car and verify that the message is gone. If not, proceed with other fixes.
2) Turn off the automatic updates
Go to Settings, then System Settings, then Software Update and uncheck the line “Automatically Check for Updates”. This will not fix the problem but it may eliminate the trigger for that error message.
After that, you will be able to drive without distractions and will have some time to find another fix for the problem.
3) Replace the 9V battery in the TCU
Open the TCU which is located behind the glovebox and replace the 9V Lithium battery that powers this module. Mazda owners claimed this step helped them a lot.
You can buy an expensive OEM battery or choose any other battery that matches the specs.
4) Check the GPS antenna
You may check the antenna itself and the connection. It may seem pretty difficult but it’s possible to check this without a dealer.
You will need to remove the instrument cluster in the Mazda 3. For other models, please consult a good manual or mechanic.
5) Replace the TCU
The Telematics Communication unit may be affected by water in Mazda cars. If it is, the only way to solve the problem with the annoying error message is to replace it.
Those modules are pretty expensive, so it’s worth checking everything twice and making sure that you are doing the right thing.
6) Go to the dealership
Dealers perfectly know that this message is common for Mazda cars. Tell them about the TSB I mentioned above and also about your suggestion to check the TCU first. Otherwise, they may start all the checkups just to kill time and earn money.
Dealers can update the software, change the battery in the TCU, change the TCU, and verify the GPS antenna is working. This will take them like two hours or so.
Can you drive with this error message?
Although you can drive with the “In-vehicle network malfunction” error message, your Mazda will lose some functions. Also, it will be pretty hard to see the trip data as the message will hang on the dash at all times.
But I assure you, the system has nothing to do with any safety equipment or vitally important control units. Even if the TCU is completely broken or disconnected, it will only affect some connectivity, GPS functions, and updates.
So, yes, you can drive with this error message and there is no need to worry about safety or other issues.
Final thoughts
The insane number of electronic control modules drives Mazda to the same place where all other manufacturers are chilling out – unreliability. That’s a pity but we should adapt somehow. I hope the tips I provided you with in this article will help you solve the problem.
If you have experience in solving this issue, please write in the comments below and let other Mazda owners save their time and money!