ChrisRCNY
Well-Known Member
Figured I'd post my success in finding why fuse 74 kept going, hopefully save someone else some headache.
It runs the O2 sensor heaters, MAF, fuel vapor purge valve, camshaft phaser solenoids, and the Charge Motion Control Valve (or Intake Manifold Runner Control Valve).
I used a short adapter harness from the ATM fuse block to ATC/ATO fuse, and a 15 and 20A push to reset ATC breaker. Replacing fuses while testing would have been expensive. Coils and motors are more likely to short than sensors, but it's still possible.
Unplugging the cam solenoids to test is easy enough, as was the purge valve. MAF sensor was unlikely, but also easy to unplug. O2 sensors are a pain, so I went looking for the CMCV...
Its in the back of the intake manifold, and almost impossible to unplug without removing the manifold first. However, the wire from the motor in it is accessible at the harness connector above the passenger wheel well, near the ECM. The wire at the connector is black with a yellow stripe, with the connector unplugged, grab the white plastic part with pliers and pull it out. A small screwdriver can lift the plastic latch off the pin and let you pull the wire out the back. Reinstall the plastic part, and connect the cables, tape off the loose pin.
Turn the key, reset codes, breaker didn't pop, no further codes.
Now I get to go buy upper intake manifold gaskets and a new CMCV, but at least I'm not digging into the entire harness looking for a damaged wire.
08 Expedition XLT 4x4, latter half of the production year with the better spark plugs. Keywords: fuse 74, O2 sensor heater short, fuse 74 blown, p0443, p0161, p0155, p0141, p0135, p0102
It runs the O2 sensor heaters, MAF, fuel vapor purge valve, camshaft phaser solenoids, and the Charge Motion Control Valve (or Intake Manifold Runner Control Valve).
I used a short adapter harness from the ATM fuse block to ATC/ATO fuse, and a 15 and 20A push to reset ATC breaker. Replacing fuses while testing would have been expensive. Coils and motors are more likely to short than sensors, but it's still possible.
Unplugging the cam solenoids to test is easy enough, as was the purge valve. MAF sensor was unlikely, but also easy to unplug. O2 sensors are a pain, so I went looking for the CMCV...
Its in the back of the intake manifold, and almost impossible to unplug without removing the manifold first. However, the wire from the motor in it is accessible at the harness connector above the passenger wheel well, near the ECM. The wire at the connector is black with a yellow stripe, with the connector unplugged, grab the white plastic part with pliers and pull it out. A small screwdriver can lift the plastic latch off the pin and let you pull the wire out the back. Reinstall the plastic part, and connect the cables, tape off the loose pin.
Turn the key, reset codes, breaker didn't pop, no further codes.
Now I get to go buy upper intake manifold gaskets and a new CMCV, but at least I'm not digging into the entire harness looking for a damaged wire.
08 Expedition XLT 4x4, latter half of the production year with the better spark plugs. Keywords: fuse 74, O2 sensor heater short, fuse 74 blown, p0443, p0161, p0155, p0141, p0135, p0102
