closed vs open loop

[Alan Roehrich]

Originally Posted by Ed Wright

GM recomends the "slap test", at least on my last trip to the GM Training center. May recomend mallets now, but I would be surprised.

The slap test works okay, on the ECM. The right hammer tap (and no, I'm not advocating beating it to death) will often expose a lot of components that have an internal fault, due to cracked boards, bad solder joints, loose pin fit, and various other "intermittents", especially those that show up on rough road, or under various sharp maneuvers.

[Patric Fox]

I was working on a Ford a few years ago which was acting the same, the DPFE valve would short and loose the 5V reference to the other sensors, causing it to stall. No codes either. Unplug it and try.