CEL 1264 and fuse #9 blowing

[aaron325ix]

Twice in as many days, all of a sudden my check engine light comes on. Stomp test gives me fault code 1264 which is EGO heater.

Fuse #9 was blown which is labeled as fuel injection electronics. I replaced the fuse and all was fine for a bit. The next day, same thing, CEL on, stomp code 1264, and fuse #9 blown.

I replaced the o2 sensor about 18 months ago with a mustang sensor.
Any ideas?

[jlevie]

That code will be set if the DME doesn't see appropriate current flow on O2 heater relay control (pin 23). That could be as a result of a bad relay, wiring fault, or a fault within the DME. I can't easily tell from the wiring diagrams whether fuse also powers the O2 heater, but if it does and there's a fault in the O2 sensor it could blow the fuse. You could pull the O2 heater relay and see if the fuse still blows.

[aaron325ix]

is the o2 heater relay the one closest to the power steering res. in the three seperate relays?

[bcrdukes]

^

If you stand on the driver side of the car at the engine bay, look at your AFM. There is a rectangular "black box" between the AFM and the shock mount tower that you can open up (there is a clip you can push.) Lift the box open. You will see 3 relays. From the front of the engine to the firewall goes like this:

Main Relay - Fuel Pump Relay - O2 Relay

The Main Relay is not elevated while the Fuel Pump and O2 relay are. The main relay will have 5 prongs and will only go in one way, the side of the main relay will have these tabs popping out which will align with the holding clips.

The O2 relay should have 4 prongs. The new part number is 61368373700 and is 5-prong but will work.

[aaron325ix]

I just happened to have one of the newer relays so i put it in and it is still blowing the fuse (#9).

With the relay out it doesnt blow. Does this mean the problem is likely at the DME?