MSefi.com read only forum (Jan.15,2018)

Does V ref initiate the on line mode? I have a situation occurring with a system that has been running for years [MS 2 Ver. 2.92 , V-3 board]. Recently the system has periods when the signal is broken to the laptop. [The performance of the car is not affected.] I first noticed multiple interruptions in a Megaview log. Yesterday ,I noticed the Turner Studio gauge display was showing on line- then off line then back on- [the running engine was unaffected]. This AM, this same on/off situation was occurring with the ignition turned on & the engine not yet started. There was absolutely no vibration or movement to the laptop or the auto. The changes seemed to be fairly regular in the time on and off- like something heating , then breaking the circuit would do. I am surmising that the V ref is being broken by F1 [the poly fuse} but because I am unsure that V ref is the signal necessary to instigate & terminate the on/off line, I am inquiring. Is V ref used for the on line signal?

The VREF comes from the main 5V power feed. If it is shorted to ground, the entire unit will shut down.

If the MS is performing normally, it can have nothing to do with the PS rails. Most likely the far more usual comms problem.

Thank you both for your replys. I understand why I was wrong with the polyfuse theory. I hadn't considered that it would shut down the entire system in the car. The laptop display has resumed normal operation. I have made several uninterrupted logs and all is well- at present. Perhaps switching laptops next would be best, as that would narrow the source of the problem to one or the other. [The problem will definitely reoccur if nothing is done.] Please advise if you feel I should take another course of action.

After switching laptops, the problem did reoccur after several hours of run time. The problem is with the auto system & not the laptop. So, I'm back to the original question - what signal is used by the laptop to determine "on line". Vcc is connected via pin 1, but I believe that if it were disrupted the engine function would cease. Timer terminals t1 & t2 both output through the db9 -but I'm not aware of their functions. I have had the on- off occur at 2 second intervals as well as extended periods of time. manual movement of the connection plugs has no effect. Tapping on the main board enclosure & relay assembly also has no effect. I'm going to check the various grounds to insure their contact today. Any other suggestions would be appreciated.

It determines the ECU is online because the ECU gives the proper response (a data stream) on RX when being sent a request for data on TX.