PTC Fuse

I have a 1995 Geo Metro 1.0L.

A 30 Amp fuse keeps blowing, after which the “Check Engine” light comes on.

The fuse is located in an underhood block, along with A/C and is labeled “PTC” which to me translates as: Positive Temperature Coefficient. The fuse was a standard blade type, not a PTC or resettable breaker.

It takes quite a load to toast a 30 Amp fuse, but I am completely baffled, and can’t find my wiring diagrams.

Does anyone have any ideas what circuit this is, or what devices might be connected? I have never seen this in any other vehicle.

I have included a couple of wiring diagrams to help with this issue it looks like the PTC fuse power comes straight from the battery then goes to the PTC relay. From the PTC relay it goes to the EFE (Early fuel Evaporation) heater (Diagram 1). As well as the ISCA and some EVAP controls (Diagram 2). Hope it helps.

I would unplu the EFE first and then replace the fuse to see if it burns out. The EFE is the most likely cause for the dead short.


Ah, enlightenment! Thanks for the wiring diagrams!
Could anyone tell me just where the EFE heater is located on a 1995 Geo Metro, and what it looks like or is attached to? Neither Chilton’s no Haynes seems to have heard of it, and I can’t seem to find any device with the specified colors of wires.


It should have 2 wires. 1 red and 1 black. It is mounted underneath the throttle body. Hope it helps.