Troubleshooting Communications Issues with the MegaSquirt and MegaSquirt-II


MegaSquirt communication troubleshooting

Usually, all you need to get communication with a MegaSquirt is to make a new project in TunerStudio, and have TunerStudio detect the ECU. We have a video of how to do that here:

If that doesn’t work, here’s how to troubleshoot what is going wrong.

Check to be sure your ECU is powering up

Many of our newer ECUs make this 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 V2.2 and 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 some PNP units also do not have status lights. If your ECU does not have status lights, check if its 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 and do not have a visible indicator if they blow. 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.

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

When the lights are on, but nobody’s home

If the ECU is powering up, but does not respond when TunerStudio attempts to detect the firmware, try using the Port Check utility. This program (currently Windows only) checks all available COM ports and sends tests commands to them, then reports how the ECU responds.

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 finds a response, it will report a firmware version.

If Port Check does not report any COM ports, try reinstalling the driver for your USB adapter. Use this driver for the DIYAutoTune USB-2920  as well as the MS3 onboard USB.

If Port Check does not find the ECU, try connecting the boot jumper or bootloader wire (consult the documentation for your MegaSquirt version), and try reloading firmware using TunerStudio’s firmware loader. This can often restore communication caused by setting glitches, such as nonstandard baud rates or settings that create unanticipated errors. For example, older firmware could crash if you set the number of trigger wheel base teeth and trigger wheel missing teeth to the same number, telling the ECU you had a trigger wheel with no teeth whatsoever.

If you still are not able to get communication with your MegaSquirt, contact our technical support team.