Strange problem with Truck and ScanGauge 2

I took the truck to mechanic to get a smog test, I had left the SG2 inadvertently plugged in. When I go to pick up the truck after work, the tech inquires about the SG, I explain the live functions, etc. He then takes me to the truck and tells me that the truck wants to stumble unless it's plugged in, but runs fine with it plugged in (he was wondering if it had some kind of kill associated with it.

The tech starts the truck, runs fine. Then unplugs and it stumbles and dies. Tries to start with it out and it stumbles and coughs and dies. Plugs in and runs good.

I drove it home and ran fine. Later that night it ran rough at times, but it was cold on a short run. Parked it and unplugged the ECU fuse for a day hoping a reset would help. Today started it up with fuse plugged in but not the SG and it does the same thing, stumble, cough, die. Plug in SG and it runs good!

Any idea's? I'll give SG a call in the morning, but I'm out of their posted hours ATM. I'm hoping unplugging when it was running didn't mess up the ECU somehow...

Incidentally, I've had the SG plugged in for the last 5 years or so without issue. But then again, I never unplug it..?

 

OK, just an update on this one.

I contacted the SG folks and they appear to be stumped, never having heard of a problem like this one. They were very nice though.

I changed the battery, resetting the ECU in the process, made no difference. Problem remains.

I talked to a local Toyota/Lexus specialist about the problem, and after going over the whole story, he said it sounded like a bad ECU. Maybe something has shorted out inside the ECU but with the SG2 plugged in, something "backfeeds" into the ECU to allow it to run. Kinda makes sense to me, even if it is a little "out there".

So I'm looking at inspecting the ECU over the weekend, to see if there is something obvious or a loose plug or something stupid. I'll also get a number off the dude and start looking for replacements. Seems they can go for a good price new, so I'll look for a working pull first.

Mechanic said these ECU's can't really get "flashed", I've also read this online. Anyone have anything different? Any input would be helpful on this problem. TIA

 

I have ran my sg in my 98 taco 3rz/4cyl for years and never had any issues. I've also never unplugged it...this has me curious. I will unplug it tomorrow and see if mine acts up. What year, engine is your rig?

 

'01 Pre-runner, 2.7 engine.

I dont really think the SG is to blame. Especially if the ECU can't be flashed, how could the SG corrupt the settings? As for a possible hardware failure, I again doubt the SG is to blame. No more to blame then any other obd2 reader that's been plugged in.

That's said, it would be a different story if a second occurrence were to turn up. But it surely would have come about before now.

 

Anyone near you that has another scan gauge to see if a different scan gauge does the same?

I bet you have some pins in the plug that are shorting when the gauge is absent.

 

Thanks for the suggestion. I don't know anyone else with an SG. But I plan on pulling the obd2 plug out this weekend and look for shorts/oddities. I also want to look at the ECU, get a model # off it, look at condition, etc. I'll report back.