Troubleshooting Communications Issues

Troubleshooting Basic Communications Issues

Communications issues can be frustrating when you’re in the middle of an important project and trying to do burnies on track with the boys but fear not! They are usually very simple to fix with a few easy steps. We are going to go over some basic fixes for communications issues here, and in a following article we will go over some more advance steps for more complicated cases.

Is the ECU Powered Up?

This sounds like a super dumb question, but you’d be surprised at how often we have customers where the root cause is simply a lack of ECU power.

Many of our newer ECUs make checking for power easy: The MS3Pro EVO and Ultimate, and most of our plug and play units, have a set of status lights. Check to be sure the ECU has the lights indicating 12-volt AND 5-volt power on. If both lights are on, you can move on to the next step.

The V3.0 MegaSquirt units have lights on the side of the case, but the tuning software sets their function and it’s not uncommon for all three lights to be off even when everything is working correctly. Same goes for the internal lights on the V3.57 circuit board. MicroSquirts and a few PNP units do not have any status lights. If your ECU does not have status lights, check if the 5-volt VREF wire (typically gray, if using one of our wiring harnesses) has 5-volt power with the key on.

If the ECU is not powering up, first confirm it is receiving 12-volt power from the wiring. (Note that the MS3Pro Ultimate needs 12-volt power on both the keep alive power and switched power, and some plug and play units need the main relay to turn on.)

The MS3Pro lineup has internal fuses. These are very small surface mount devices and do not have a visible indicator if they have blown. So, if the ECU is not powering up, check these with a multimeter and replace any fuse that does not have a near-zero ohm reading across its ends.

After those tests, the next thing to check is to be sure the 5-volt VREF wire is not shorted to ground in the external wiring. A short here can trigger internal protection (either the MS3Pro’s replaceable fuse, or self-resetting short circuit protection) and shut down the ECU until the problem is corrected. A bad sensor could cause the 5-volt VREF too short to ground. The best way to test this is disconnect anything using 5-volt VREF and test with a multimeter to see if you can find the short or at least make sure the ECU has 5-volts.

If the ECU is still not powering up after checking all these factors, please contact our support department.

USB-Serial Adapters

If you are using a USB to Serial adapter, you will next want to look at what port the USB adapter is using.

Using your search bar at the bottom left of your PC, search for “Device Manager” and click on it. Once the window opens scroll down to an entry called “Ports (COM & LPT)”. Click the arrow next to it to expand the menu. You should see an entry that looks like “USB Serial Port (COMx)” where x is the number of the port it has grabbed. If it’s grabbed a port number higher than 4, we recommend changing it to a lower number. Double-click the USB Serial Port item. Then select the Port Settings tab at the top of the box that pops up and click the button marked “Advanced”. You will see a new screen where you can specify the COM port number; set it to a number less than 5 that is not already in use. Then click OK to close that screen, and OK to close the Properties box. This will set your USB adapter to a lower port number. If the port number is already lower than 5, we can leave this setting alone.

If the USB adapter port does not show up, or shows up as an unknown device, download and install the correct FTDI driver from this link

Installing the FTDI driver is a good practice whenever using a new USB to Serial adapter, so you may want to do this up front.

Port Check

If the ECU is powering up properly and you have a valid COM port, but the ECU still does not communicate with TunerStudio, then we will need to perform a Port Check using the Port Check utility. This program checks all available COM ports and sends test commands to them, then reports how the ports respond.

To use this test, close Tunerstudio and any other programs that might use the COM ports first. Power up the Megasquirt and connect it to your PC, then run the Portcheck.exe program and watch it scan the ports.

If it receives a response from the ECU, it will report a firmware version. If it reports a firmware version the fix may be as simple as creating a new TunerStudio project and have it detect the firmware as you normally would. If that doesn’t fix your issue, contact our customer support team with your issue.

If the Port Check comes back with “0 Valid Ports Found”, there is likely another program using the port. Make sure every program that could be using the port is closed before running a Port Check. Or this is almost always a laptop/USB adapter problem. Try reinstalling the driver for your USB adapter. Use this driver for the DIYAutoTune USB-2920  as well as the MS3 onboard USB.


These are the basic steps to troubleshoot communications issues you might be having with your MegaSquirt unit. We will have a follow up article on advance troubleshooting where these steps will be more involved and will require you to open your MegaSquirt ECU for access to the PCB.

We appreciate you following along and please feel free to reach out to us at any time with any questions you might have!

Have fun and good luck!

DIYAutoTune Products Used:

USB to Serial Adapter