Dave Witman

When checking codes on friends 91 vette the engine fan comes on when jumping aldl connector pin a-b. The ses light works normal but engine fans run the whole time jumper is installed. Also my scanner will only stay linked for a few seconds.

Sid.123

Mines the same on my 86. The fan runs all the time with the pins connected I think this is normal...
cant help though with the scanner as I don't use one

VikingTrad3r

It's supposed to come on.

Kevova

It's called Field Service Mode. Ecm will cycle things it controls, fan is the most noticeable one. What brand and/or model of scanner are you using?

ImBatman

Interesting. I assume this would be the case for a 1990 base?? When I jump the terminals I don't notice the fans coming on. Does this indicate a problem? I know the fans come on when they need to while driving and idle.

Wade

Kevova

Not necessarily. If you were having trouble with ecm turning on fan(s); typically with a/c or dual fans. There is also a temp switch to turn on cooling fan which applies ground to cooling fan relay. Using field service mode you can back probe ecm controlled relay or solenoid to see if it is recieving signal to turn on.

Dave Witman

Cornwell scanner 3499. Scanner only stays linked for about 10 sec. Will link again but only for a short time. I tested unit on my 04 truck and it worked fine. Have a snapon MT2500 on the way.