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V3 MicroSquirt® - QuickStart Guide

Connecting Your MicroSquirt® Controller and Your Laptop PC

This troubleshooting guide is intended to help you sort out connection issues between your laptop and your V3 MicroSquirt® controller. Typically these are things like TunerStudioMS error messages of the sort "Controller code version does not match signature ..." (which is caused by an INI file not matching the loaded code, in this case) or "ERROR: Command not recognized, e=0xE1" which usually means a serial port connection with a MegaSquirt® controller connected to it was not found.

There are certain things that have to be in place and functional for your V3 MicroSquirt® controller to talk properly to your laptop:

Here are what you need to check if your laptop PC does not talk with your MicroSquirt® controller:

  1. The first thing you must do is set the ECU Type (under 'Fuel Set-Up/General') to match your hardware (MS-II or MicroSquirt™), MegaTune will not let you change anything else until you do this. Do not change settings, expect the stim to work, load an MSQ, etc., until you have set the ECU Type (MS-II = 1, MicroSquirt® = 2, the MS-II Sequencer will be 3). This setting applies to MS-II derivatives with code 2.88 or higher code only.

  2. With a MicroSquirt® EFI controller, be sure the DB9 and mini-stereo connectors are fully seated.

  3. Check the serial port on the laptop/PC. We need to verify that your laptop/PC actually has a functional serial port before proceeding.
    1. If you have a USB/serial adapter instead of a built in serial port:
      • You may have to play with the USB adapter COM port settings in Windows for the adapter to get it to work (see Control Panel/System/Hardware/Device Manager).
      • Make sure that your com port settings are correct for your serial port or your USB/serial cable. For example, change the baud rate (under 'Start/Control Panel/System/Hardware/Device Manager/Ports (COM & LPT)') to 115200 for MS-II.
      • Try re-installing your USB driver.
      • Check this thread on the support forums for new info: USB to Serial Adapters.
    2. First check that nothing else is using the serial port, such as a fax/modem. Make sure the downloader is closed (TunerStudioMS and the downloader shouldn't be open at the same time, they will interfere with each other). To find if other programs are running, first try 'Ctrl-Alt-Del' all together (but just once). This should list all the programs that are running. Look for any that *might* be a fax/modem (you must keep systray and explorer). You can kill any extraneous programs you find directly from the dialog that springs up when you do ctrl/alt/delete, or you can look in 'start/program' to see if any fax/modem software is listed and configure it to not start on power-up. Alternatively, you can also type msconfig in the run box to see what is starting and block any program from loading.
    3. On your laptop PC, be sure to disable any other programs that might try to use the serial port, etc. This includes Infra-red communications (IrDA). For example, if you have your IrDA switched on it might go looking for a connection at regular intervals (usually in the middle of something important).
    4. You may have to try different com port numbers (COM1, COM2, ... COM99) to find out which com port number is assigned to the physical connection you are using for MegaSquirt. Be sure to note which com port you successfully used for the loopback tests, you will need to enter it later into other downloading and tuning programs.
    5. Try re-installing your USB driver.
    6. Go to 'Communications/Setting' and 'Detect' the connection to your MicroSquirt® controller, then 'Accept' the connection when it is found.
    7. Search the forums at for new info on: "USB to Serial Adapters".

    8. If you have another computer available (a laptop or another desktop, for example), you might want to try that to connect to your your V3 MicroSquirt® controller - this can help rule out a damaged or mis-configured serial port on the computer.

  4. Check the power supply. your V3 MicroSquirt® controller must be powered in order to communicate.

  5. Check the serial cable and serial circuit. You need to ensure that you cable is straight-through and not a null modem cable, as well as that it doesn't have other functional problems. To do this use an Ohmmeter to verify that your DB-9 serial cable is truly a pass-through and not a null modem. All DB connectors have the pin numbers molded into the plastic insulation around the pin holes on both male and female ends. The numbers are quite small and you may need a flashlight and magnifier to see them, but they are there. Check that pin 1 on one end is connected to pin 1 on the other end, then do the same check for pins 2, 3, 5 and 9.

    If all these check out, you can proceed, otherwise you need to get a different cable. To repeat: On the cable, pins 2, 3, & 5 should all be connected and "e;straight-through".

  6. Check for a functional processor. If you suspect the processor itself, the first thing to try is to reload the code (see the next step) since this is free and will often solve a processor problem. Of course you need a working serial port to do this, so you may have to try all the other steps first.

  7. Check that you have appropriate code loaded on the processor. Your V3 MicroSquirt comes loaded with code and should communicate with the laptop/PC. It isn't impossible that this was missed at the factory, so if you suspect you have no code, follow these steps:
    1. Download the code from the Internet. Get the latest version of MegaSquirt-II code here:
    2. Power down your V3 MicroSquirt® EFI Controller,
    3. Ground the bootloader wire (Ampseal pin 15),
    4. Power up your V3 MicroSquirt® controller.
    5. Start the downloader program (make sure TunerStudioMS is not running), and select the appropriate COM port (from the loopback tests) and speed (115200 for your MicroSquirt® controller),
    6. Select the appropriate .S19 file (that you downloaded above), and the downloader will read, write and verify the code to the processor in about 10 seconds or so.
    7. The process ends with a message like "Verification succeeded, 999 records total (4 skipped)."
    8. Shut down the downloader program.
    9. Remove power from your V3 MicroSquirt® controller (disconnect the stim).
    10. Un-ground the bootloader wire.
    11. When you power your V3 MicroSquirt® controller back up again, it should come to life running the newly loaded code.

  8. Install and configure a program on the laptop/PC to talk to MegaSquirt®, this is usually TunerStudio. For TunerStudioMS details, see the TunerStudio website.

  9. Open TunerStudoMS and set the com port (from your loopback tests) and the baud rate (115200 for MegaSquirt-II) under 'Communications/Settings'.

  10. If you have changed code version (or loaded code for the first time), you may need to change the INI file to match the new code. The files have names like "megasquirt-II_2905.ini", where 2905 indicates the 2.905 code it is to be used with.

    (New code versions (2.889+) have their own INI, so for example 2.890 code (Monitor_v2.890.abs.s19) has a specific 2.980 INI (megasquirt-II.ini.2.890).

    You will find the INI files here: and the code S19 loadable files here:

    Note that all older 2.XY (prior to 2.889) use the same 2.X INI file. For example, the 2.35 code uses the 2.3 INI file. This is the way the older code upgrades are designed. Major revisions were incremented by +0.1 and require a new INI file, minor revisions (+0.01) use the same INI file.)

    You may also need to install a fresh INI file if you have edited it manually, and made any mistakes (which is easy to do and often shows up as a comms error - typically the controller will connect with the tuning software, but then it will go offline after a second or two, and not re-connect unless the power is cycled - starting the process again).

    You can select new INI to match code you have loaded by:

    1. going to 'File→Project→Project Properties' in TunerStudioMS,
    2. checking the 'Other' box,
    3. clicking on 'Browse',
    4. surfing to the INI, and
    5. double clicking on the correct INI.

  11. Be careful when using a vehicle battery charger with a laptop AC charger plugged into the same wall receptacle! Using an AC-powered battery charger connected to your battery while powering your laptop from an AC power charger (a.k.a. power brick) can cause an unintentional ground path return loop. Many battery chargers have the negative lead connected to the AC line power ground thru the third prong line cord. In other words, the high current battery charger source negative terminal output is also tied to the line cord ground blade on the AC line plug.

    Also, many laptop charger brick units have the third prong connected to the laptop ground, including the serial port and USB. When both the battery charger and laptop power brick are plugged into the same outlet, or even any outlet sharing the same ground return to the electrical panel, these circuits are now electrically connected and can flow a lot of unintended current! Now, if for some reason the battery charger negative lead clamp falls off of the battery or has a bad clamp connection, the least resistance path for the battery charger negative lead is a path thru the laptop and serial connection back to the MicroSquirt. p>Needless to say this can lead to catastrophic consequences to the MicroSquirt and potentially your laptop, these devices are not designed to handle the many amps that a battery charger can deliver. Battery chargers are electrically noisy to begin with and should be avoided with any electronics, but if they must be used then it is best to run the laptop off of its internal batteries or ensure that the laptop does not have a ground return thru the line cord plug.

If you have any questions or problems that can't be answered from the links above, or a search the MicroSquirt® manual:

you can ask questions at the MicroSquirt® support forum which is at: Click the links for more information.

Your V3 MicroSquirt® controller and MicroSquirt® controllers are experimental devices intended for educational purposes.
Your V3 MicroSquirt® controller and MicroSquirt® controllers are not for sale or use on pollution controlled vehicles. Check the laws that apply in your locality to determine if using a V3 MicroSquirt® or MicroSquirt® controller is legal for your application.
©2011, 2023 Bruce Bowling and Al Grippo. All rights reserved. MegaSquirt® and MicroSquirt® are registered trademarks. This document is solely for the support of V3 MicroSquirt® boards from Bowling and Grippo.