1999 GMC Savana eng I fuse

Hello, my info shows 02 heater circuits. If you could check codes, it might tell you which one. You could unplug the sensors, one at a time.

Also the crank sensor--maf sensor and the evap system you were talking about. Does the fuse blow before or after you turn on the key?

You might could leave the fuse out, do an ohms test from circuit side of fuse, dead, to the other end of voltage wire for whatever circuit your testing, maybe the problem circuit is open? Like hunting a needle in a haystack. You could also separate each branch from the main circuit, one at a time, use an inline fuse or circuit breaker with a jumper to battery voltage, see if one of the circuits will blow the fuse or throw the breaker. Sure sounds time consuming. I can't think of anything else.

I've never checked 02 sensor voltage wires with engine turned off, don't know if one of those circuits would show ground? The back wire on each 02 sensor should show ground, that is ground for the heater circuit. One of the wires for each sensor signal circuit, does show a ground symbol, I've never checked it the way your doing.

The autozone site has free wiring diagrams, you'll have to register your vehicle, it is free.

Also try www. Showmetheparts. Com/airtex/ when the site comes up, click on technical resources. It will ask for y--m--m just follow the links. It is mainly engine wiring and component locations. I don't know if I'm supposed to post links to other web-sites on this forum. This post may get erased. I have no connection to those sites.