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Subaru Impreza 2007, scangauge and check engine light

So I’m driving along with everything fine till I pull into a neighbors driveway to drop off some stuff. As I pull in, the check engine light suddenly comes on and the cruise control light starts blinking. As I have a scangauge II always connected, I put the car in park and check the code. It comes up as P0000. I get on my Droid III and google it - all I see is “null code” so I clear the codes and everything is fine. I figure “that’s odd, but whatever”. I drive home (about 1000 feet) and park and shut the car off and go inside to mull this over.

I go back out to check out the scangauge again and it requires starting the car to read out the codes. The car won’t start. The battery is fine, and in fact it does the “rurrr rurrr rurr” strongly for 10 times before I figure it’s not starting. I wait about 30 seconds and try again - same thing. I wait about an hour or two and try again and it starts this time right away, but then stalls right away. Start again and manually give it some gas and it keeps idling weakly. I’m able to back out and drive a short distance and come back without a stall. I let it sit for the weekend (no shops open anyway) and start it monday morning with my AAA card out… and it starts fine and runs fine all day. I basically forget about it.

About a week and a half later, I’m driving along a country highway at 55 Mph, and the same thing happens. Check engine light, cruise control light blinking and the cruise actually cuts out so I’m losing speed suddenly. I run the scangauge again and same code. The car keeps running fine though, I’m able to drive it back (w/out cruise control) the 5 miles home. Nothing out of the ordinary.

I go inside and google this some more, and there’s some posts about the Scangauge causing this - but I’ve been using it for about 4 years w/out this happening. That said, about 2 months ago, there was a recall, and they flashed the ECU with some update so maybe that changed something, but still - worked for months before this happened. I had to get to work etc so I just cleared the code again, and so far 3 days without a recurrence. Currently I’m thinking about waiting to see if it happens again and going to Autozone and have them read the code to see if it really is the Scangauge not reading the code right or whatever… Any ideas though?

“I have a scangauge II always connected”

This might be the problem. I doubt Subaru’s software is designed for that.

I too also doubt the trouble is being caused by the scangauge. It just monitors things as far as I know. I would suspect a bad power connection somewhere is the real cause. Since you say the engine wouldn’t start at one point I would look for a problem with the following: Main Relay, Ignition switch, ignition system, in that order. The Main Relay effects a lot of engine components. I think it has a double set of contacts and the set for the engine area may have faulted while the set for the ECU worked ok.

Maybe the pcm can be reflashed. Maybe they’ll do it for free. Maybe that will fix everything. Maybe I’m wrong.