Scangauge not always restarting
 

My older SGII (version 3.17) goes off when I kill the engine (newer versions can be set to stay on), but it often doesn't restart. It always starts after the car has been off for a longer time, but if I kill the engine (either EOC or at a red light) then after starting up the SG's display turns on showing data from the moment it was killed, but blinks off after a few seconds. There seems to be no difference whether I use the engine kill switch or if I key off, nor if it is only one or multiple engine kills in a short time.
To make things weirder, after a while (10 minutes? 15?) the SG suddenly comes back to life as if nothing had happened.

I'll add that I have a second, newer SG (version 4.06) wired in parallel and recently it too has gone to sleep for a few minutes 2 or 3 times, even though it is set to stay on when the engine is killed.

Any ideas as to what is happening?

I'm not an user of SG II as you know but I have some experience with electronics. Recently I was "fighting" the issue with MPGuino after installing of kill switch. Killing the engine by cutting off the solenoid was causing electric noise which was messing up with guino. The same issue was during starting the engine. So I needed to cut the noise.

First I've mounted a noise filter on the cable providing power to MPGuino and then diodes on the kill and start switch to cut the voltage pikes.
Cutting the noise from a kill switch

It's working very well right now and I can stop and start the engine without any effect on MPGuino.

So first of all maybe you should check if there are any voltage pikes or other noise during killing and starting the engine again. Then it should be fairy simple to cut the noise.
One more question - SGII is acting weird when you're killing the engine or during restarting it? If when you're restarting the engine let me know if that is when you're using starter or bump starts too.

The engine is killed via a NC relay, the engine starter is a NO relay wired in parallel to the ignition. Iirc both relays already have a diode. Are you suggesting that I should add a diode between the COM and +12V pins of the OBD socket? What kind of diode?

The older SG goes to sleep whenever the engine stops (as it should), and doesn't work when the engine starts (bumped or keyed on). Sometimes it will suddenly start working after a long while.

I don't know what is causing SGII to wake up after engine stops. I presume it reads some code from the ECU. We can investigate this issue together when we'll meet I have oscilloscope and two diagnostic interfaces so maybe we'll find a solution if SGII hanging is caused by any electrical noise or something else.
Longest weekend of Modern Europe is coming so we can try to meet and investigate it. And we've planned to meet anyway so maybe we can try to kill two birds with one stone :)

I've noticed sometimes my SG-II (don't know the version number, sorry) doesn't come on as well. If I hit the home button, it wakes up immediately and resumes working.

It hasn't bothered me enough to contact the company.

Contact Us : Linear Logic - Home of the ScanGauge

I've had that happen, too. (hitting the home button waking it up immediately)