HO2S - Heated Oxygen Sensor question

[gregr]

I am trying diagnose an electrical problem with my 93 MTX. The Fuse #5 blows out constantly.

Ford Manual says this fuse controls the following:

- Electronic Cluster
- Rear Defroster switch
- Electronic flasher
- Backup lamps
- Heated Oxygen sensor
- Illuminated / Keyless entry module
- Brake Interlock solonoid

Is the HO2S the same as the O2 sensors that are screwed to the Y pipe? If so, what hard would be done by disconnecting them temporarily and driving the car?

This problem is getting really annoying.

Everytime the fise blows, I lose the turn signals (not the hazzards), the backup lights, the climate control, and rear defroster. Sometimes the fuse would last a while and them blow at random. Not it looks like it's shorted all the time.

Thanks in advance.


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Greg Raciti
SHO Forum Webmaster

93 Emerald Green MTX
Performance Plus high flow stainless Y-pipe
Scott 2.5" Stainless
Exhaust with Edelbrock mufflers
SHOShop Cold Air Induction
SHOShop Underdrive Pullies (to be installed)
Romar Enterprises Subframe Connectors
SHO NUT Performance Aluminum Subframe Bushings
24mm front sway bar
26mm rear sway bar
Energy Suspension poly bushings
SHOShop LPM
SHOShop UDP's (coming soon!)
IPT triple gauge pod with Autometer - Volts, Oil Pressure, and Water Temperature Gauges

 

[fredhurderjr]

Greg -
The culprit may be having the fan on the ECC turned up all the way. Lower it, or drop it all the way to the bottom, & see if that does it. It sounds more like an electrical short somewhere than anything.

To answer your question (part a)
Yes, the Heated Exhaust Gas Oxygen sensor (HEGO) is your O2 sensor(s) screwed into the Y-Pipe. With no feedback from the O2's, your car will throw codes at the least. I'd hazard a guess it wouldn't get out of Open Loop, either, which will run your car very rich (& work over your cats). You know what that does...

Good luck buddy.

 

[gregr]

Fred,

The fuse has blown with the climate control reading "OFF". It's also done it when I was not touching the breakes, the rear defroster OFF, and not backing up. The only common denominator was that the lights were on on every occassion, until now. The only thing I have not checked are the O2 sensors.

I need to get in there with a voltmeter and check it all out. My Helm manual does not have wiring schematics. Anyone have a schematic?

Thanks.



------------------
Greg Raciti
SHO Forum Webmaster

93 Emerald Green MTX
Performance Plus high flow stainless Y-pipe
Scott 2.5" Stainless
Exhaust with Edelbrock mufflers
SHOShop Cold Air Induction
SHOShop Underdrive Pullies (to be installed)
Romar Enterprises Subframe Connectors
SHO NUT Performance Aluminum Subframe Bushings
24mm front sway bar
26mm rear sway bar
Energy Suspension poly bushings
SHOShop LPM
SHOShop UDP's (coming soon!)
IPT triple gauge pod with Autometer - Volts, Oil Pressure, and Water Temperature Gauges

 

[Rob94]

Greg,
Perhaps the wires for one of the O2 sensors hung low enough to touch the exhaust and melt the coating off. It sounds to me like something is grounding itself out.....and if the fuse blows when nothing on the circuit is being used that is in your control, then the O2 sensors would be the logical place to look. Good luck.

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Rob
White 94MTX
K&N Filter otherwise stock

 

[gregr]

OK. Now what's up with this?

If that fuse controls the H2OS sensors, then wouldn't that mean the sensors are not functioning? Or does that just mean the heater elements are not working? I ran the EEC self test. I get (111) which is all systems pass. If the sensors were dead, would that throw a code at me?

i am really confused here.



------------------
Greg Raciti
SHO Forum Webmaster

93 Emerald Green MTX
Performance Plus high flow stainless Y-pipe
Scott 2.5" Stainless
Exhaust with Edelbrock mufflers
SHOShop Cold Air Induction
SHOShop Underdrive Pullies (to be installed)
Romar Enterprises Subframe Connectors
SHO NUT Performance Aluminum Subframe Bushings
24mm front sway bar
26mm rear sway bar
Energy Suspension poly bushings
SHOShop LPM
SHOShop UDP's (coming soon!)
IPT triple gauge pod with Autometer - Volts, Oil Pressure, and Water Temperature Gauges

 

[Rob94]

Hmmmmm....very good point. And now I'm confused as well. Let me do some research and try to find an answer for you Greg. I have MANY manuals at my disposal at my next door neighbor's (he is a mechanic). Will try to post a reply within an hour or so.

------------------
Rob
White 94MTX
K&N Filter otherwise stock

 

[Rob94]

Greg, here's what I have come up with......Sensor #1 has two wires going to it....a red/black and a purple/orange.....Sensor #2 also has two wires going to it....a dark blue/light green and a purple/orange......it appears that the purple/orange wires "merge" together at some point, and are protected by Fuse #5, a 15 amp, and the other two wires connect to ins 29 and 43 on the Powertrain Control Module......an educated guess would tell me you have heater element problems or a bare wire somewhere......I can scan in the page I'm looking at if it would help you...just let me know

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Rob
White 94MTX
K&N Filter otherwise stock

 

[gregr]

Rob,

That helps me actually. It makes sense that the heater elements are fused, while the sensor portions go to the PCM. A scan of that page would help ALOT. Here's my email [email protected]

Thanks.



------------------
Greg Raciti
SHO Forum Webmaster

93 Emerald Green MTX
Performance Plus high flow stainless Y-pipe
Scott 2.5" Stainless
Exhaust with Edelbrock mufflers
SHOShop Cold Air Induction
SHOShop Underdrive Pullies (to be installed)
Romar Enterprises Subframe Connectors
SHO NUT Performance Aluminum Subframe Bushings
24mm front sway bar
26mm rear sway bar
Energy Suspension poly bushings
SHOShop LPM
SHOShop UDP's (coming soon!)
IPT triple gauge pod with Autometer - Volts, Oil Pressure, and Water Temperature Gauges

 

[sdpatt]

You might want to check the fuse before and after you shift into reverse. The backup lamp circuit on dfwsho's car had a short that caused this fuse to blow whenever you shifted into reverse. A temporary workaround is to unplug the backup lamp switch that is mounted on the top of the transmission, straight down from the air inlet hose. If the short is in this circuit, it could be the backup lamp switch or the wiring downstream of the switch to the backup lights. The metal support plate above the backup lamp switch that holds the wiring bundle had sawed a groove into the wires since they were not tied down to the plate. Probably another unfinished job from a clutch replacement.


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Scott

1991, 254K miles, glass hood, police grill, SVO shifter, Catz fogs,
K&N, 73mm MAF, Superchip, PP Y-pipe, Borla cat-back, 190 lph pump
Eibach/Tokico/polyurethane, SHO Shop front & rear strut braces,
16x7.5" Moda R1, 225/55ZR16 Bridgestone RE730, -1 deg camber x 4,
6 disc CD, Class II hitch, Silver award at SHOklahoma Car Show