Must scan tool be connected to car battery that you are testing?

[GNRick]

My cig. lighter doesn't work so I used my other car's lighter. Hooked up scan tool in aldl port and car died out. When I connected the scan tool to the battery of the car that I was scanning, it worked fine. Why is that? And another question........blm was 118, no matter if I lowered FP or raised it. I am using Eric's chip. I know it should be 128 but does Eric progam his chips to read 118? Thanks.

 

[notacarlo]

other than getting false battery voltage readings....no prob.

BUT

if your battery is crapping out and you can't see that, then you could misdiagnose any other sensor reading.

 

[GNRick]

I think the battery on both cars is good. First the car kept dying out, then I had to give it gas to keep it going. It just didn't like the scan tool hooked up to it unless I used the same battery in the car that the scan tool was hooked up in.