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Electrical Diagrams -- A Little Help, Please

S

Scorpion8

Hard-core CEG'er
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Jul 10, 2008
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I posted here about an issue with my Zetec upstream oxygen sensor. I have the Haynes Manual out for Contours, and am following the chassis electrical diagram on page 12-29. The O2 sensor is annotated on the left/bottom of the page. Here's my question: I can follow the WH line directly to the ECM junction plug pin 44, and the heater power line VT/YE directly to Fuse 13 in the engine fuse box. The ground line BK/YE is easy to trace, and goes to the battery ground after a solder connection at S57.

The real issue is the sensor signal return line BN, which goes to a solder junction at S58, and the other lines that connect to that thru various other lines connect to Pins 24, 25, 46, 60 and more! If my ground issue is on any one of those, wouldn't it show up as other codes on the CEL? Those all seem to have as a common item the A/T selector lever indicator, so is that simply providing a "run" signal to all these sensors, as otherwise why would the leg of the O2 sensor be tied in to the TSS, Intake Air Sensor, Exhaust Gas Pressure Sensor, etc?

Anybody with some electrical knowledge -- a little help?
 
Send me a copy of the wiring diagram and I'll take a look at it for you.

There are 4 wires going to the sensor, as you already know. Two are for the heater circuit. There should be 12 volts to one any time the car is running (maybe key on engine off too) and ground to the other under those same conditions. If you have that, the heater circuit is good. Have you established that at this point?

The other two are the signal wires, and they are the ones that run through all sorts of junction blocks. I will look at the diagram if you can send it to me but I don't see any reason why you couldn't run a new wire directly from the sensor to the ECU connector and bypass them all. I've bypassed the harness to run other sensor wires directly on dozens of cars and it's never been a problem.

Like I said, figure out if the heater circuit is good FIRST. Then worry about running new signal wires if need be. A lack of power or ground to the heater will cause that code, just as an open in the signal wire could.
 
Thanks I will look at it more closely tomorrow.

Are you 100% sure that power and ground are making it to the sensor connector at the heater terminals?
 
mcgarvey said:
Are you 100% sure that power and ground are making it to the sensor connector at the heater terminals?
Click to expand...

No, or er, depends. I have 12+ volts across Fuse 13 in the engine compartment fuse box. That should go direct to the O2 sensor via the VT/YE wire. But when I checked the terminal end of the O2 sensor, the VT/YE wire should have 12+ volts across it and I measured at the female end to the BK/YE ground wire and to chassis ground and got nothing. However, does the transmission have to be in RUN position to have a signal to the BN wire? I don't see anywhere where the first pair VT/YE & BK/YE have anything to do with the WH & BN pair of wires.

Also, does the fuse block in the engine block fuse box come up for access underneath? I seemed to be canted when I first checked, so I pushed down and it sort of "popped" in. I couldn't figure out how to get it out to check the electrical connections underneath.
 
I Wish the Guys Who Wrote These Books ....

I Wish the Guys Who Wrote These Books ....

..... had to use them every friggin' day of their lives!

So I pull the battery on my Contour today to gain access to the engine compartment fuse box. I don't have power to the upstream O2 sensor on my Zetec, but I do have power to Fuse 13 of the fuse box. According to the diagam posted above, it should be a straight wire from the load side of Fuse 13 to the O2 sensor via the VT/YE wire.

And if you believe that, I have a some ocean-front property in Nevada to sell you.

I was checking the fuse connection, and did a continuity check between the fuse load side and the O2 sensor. It should have continuity, but if it did, it should thus have power. Nope, no continuity. I pulled the fuse box up to check the connections underneath and there isn't a VT/YE wire in sight going into the fuse box. I can't determine which wire comes off the fuse because there is some internal wiring in the fuse panel and then you get snap on connections underneath in a completely different order. I did a continuity check underneath and found which prong corresponded to the load side of Fuse 13, but that matches a OR/BU wire.

There isn't an OR/BU wire anywhere on my wiring diagram.

Can I just tap off the wire that comes off Fuse 13 (make sure it has power in it, and not when the key is off also which seems true before I pried around underneath) and run that to the O2 sensor connector on the radiator mount to connect up to the VT/YE wire at the connector, and then run a new ground wire off the O2 sensor connector BK/YE wire to some frame grounding point? This would replicate and simplify two of the four wires of the O2 sensor.

Any thoughts?
 
Let me put it this way, because this is what I'm 100% sure of: If the engine is RUNNING, regardless of what gear you're in, there should be power and ground to the heater + and + terminals of the upstream 02 sensor connector.
 
Well, I'm convinced this electrical diagram from the Haynes model is generic, as it's supposed to cover 5 years of Contour & Mystique models in all shapes and forms. Anybody got a real electrical diagram for these cars?
 
FIXED. I couldn't find the actual source of power for this sensor. There is a 2-conductor plus VIO/BLU & BLK (which is what the power for this sensor is supposed to be, dangling aimlessly, but for the life of me I could NOT find a corresponding connector for it to plug in to. Besides, this one went willy nilly into odd places. So I just ran a new power line from the multiple junction master plug behind the air cleaner box around the front of the car to the O2 sensor and powered it up that way. My diagram-specific power wire (VIO/YEL) seemed to be loose inside it's wiring harness so I have a feeling it came unconnected from S3005 where ever that junction is. Started the car 4 times, and the CEL hasn't come back. In fact I didn't even have to clear it, once it had 12V power again thru Fuse 13 it cleared itself.
 
Just an update. When I reported the problem fixed above, I had run a temp 12v line from the master electrical connector behind the airbox around the front of the 2.0 engine/radiator to the O2 sensor power lead. I used wire-taps since it was a temp fix, and I hate wire-taps. I went back today to do it right ....

My plan was to pull the O2 sensor 12v lead out of the wire-loom as it seemed a little loose, and just solder direct to the end of that wire, thus maintaining as much of the original harness as possible. As I pulled the VIO/YEL wire out, only abou 9 inches came and there was a melt spot. Hmmm...... So I laid the wire out to as far as it would reach, and the wire harness leads alongside an engine coolant return line and was wire-tied to that! Yikes. It had melted thru at that point. THERE'S MY PROBLEM. I cut away the wire loom there, pulled the source-end of the 12v VIO/YEL out and put a 1/4" 18wg spade connector on that end. Then I started the engine, and tested for 12v at that spade conenctor. Yup! I finished jumping across that melt-spot and removed all of the temporary wire and now have essentially original harness (improved) as I moved it away from the coolant return line and tied it off to other (much cooler) fixtures.

NOW the repair is complete.
 
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