O2 Sensor Bank 1 Sensor 1... I'm stumped...

[cjvervaet]

OK, here we go...

I'm stumped and I'm leaning towards an electrical issue. Here's what is going on.

This is for a 2007 Mercury Mountaineer Premier that has the 4.0L V6 and she's 217000 miles young.

The other day I had a error code for the O2 Sensor 01 on Bank 01 P2196 that was thrown, indicating that the sensor was stuck on "rich" and code P0132 indicating I had high voltage (1.3 volts on my scan tool).

I swapped out the sensor, for both the upstream and downstream sensors. When I fired it up, I didn't see any voltage at all being registered, and it was throwing code P0053 "Heated O2 Sensor Heater Resistance". So I had thought I had a bad sensor, I purchased some on Amazon, however the downstream sensor that I replaced was working fine and registering around .7 volts (while fluctuating) and that also matched the Bank 02 Sensor 02 readings when the engine was nice and hot (Catalytic Convertor Temp around 1200F).

So I shot down to AutoZone this morning and bought the OEM Bosch upstream sensor and installed it this morning, also checking to see if there was any evidence of corrosion or a bad wiring connection.

As soon as I hooked the battery cable back up and fired up the engine, I saw the voltage spike to 1.3 volts then settle down to 0 volts. It stayed at 0 volts during the test drive and never moved. I then got codes P0053 "Heated O2 Sensor Heater Resistance", P0135 "O2 Sensor Heater Circuit (Bank 01 Sensor 01)", P2195 "O2 Sensor Signal Stuck Lean Bank 01 Sensor 01" (which is the opposite from the "rich" code that started this whole project).

So after 2 new sensors, and 1 of those being an OEM part, I started to check more readings.

• I removed the Mass Air Flow Sensor and cleaned it with alcohol and also ensured that the wiring harness wasn't cracked.
• I removed the spark plug from Cylinder 01 on Bank 01 and inspected it. It looked fine, no evidence of charring or running a lean/rich mix.
• I checked the fuel rail pressure, it was reading around 40 PSI at idol.
• I reinstalled the MAF and checked the CFM readings and they look like the sensor is registering CFM just fine, fluctuating up and down depending on the throttle commands.
• I checked the fuse in the engine compartment for position #42, and that was fine as well.
• I also checked my intake pressure and it looks normal, reading around 5 PSI at idol.
• Air Fuel Mixture readings are around 14.7, which I believe it also at normal levels.

I'm stumped. The sensor is reading 0 volts, and I've only see it register voltage on 3 occasions, the first when I started it the first time I installed the Bosch part, and two other times I saw it move to .8 volts then settle back to 0.

Maybe the wiring harness has a crack or is damaged somewhere? Or the male connection is damaged? Or maybe the purge control valve is stuck open?

Any help would be really appreciated.

 

[cjvervaet]

OK, I think I figured it out. Like I was thinking, I thought it was electrical. So I started to trace the line and when I shined my light at the male connector, I saw a gleam of copper. So I cut back some of the conduit and sure enough, there are 3 wires that are bare and touching each other. So I think it's shorting out. What I ended up doing just for today was wrap each of the exposed wire with a plastic connector and I sprayed some liquid plastic on it. I need to find a replacement male connector, it has 4 pins. Off to eBay I go looking for the fitting. Hopefully this is the root cause.

 

[J_C]

On some Ford connectors, there is a different color insert in the connector and you might be able to remove that, pull the pins out, and reuse the connector. YMMV.

However if the wires are intact besides the insulation, first I would wonder if the whole wire is bad, why that insulation is gone, but would consider just cutting, and soldering them back together with heatshrink tubing over the bad area, if there is enough slack to do so. Some people would try to avoid cutting and soldering and use self-fusing silicone tape insulation. I'd get a major brand if you were to try that, not some generic chinese stuff.

There's a Ford connectors ID PDF file linked in my sig below, though I don't know if that specific connector is in it, but if you get a part # it might be easier to find online. On larger connectors there is a part # on them but I don't know about that one.

 

[cjvervaet]

On some Ford connectors, there is a different color insert in the connector and you might be able to remove that, pull the pins out, and reuse the connector. YMMV.

However if the wires are intact besides the insulation, first I would wonder if the whole wire is bad, why that insulation is gone, but would consider just cutting, and soldering them back together with heatshrink tubing over the bad area, if there is enough slack to do so. Some people would try to avoid cutting and soldering and use self-fusing silicone tape insulation. I'd get a major brand if you were to try that, not some generic chinese stuff.

There's a Ford connectors ID PDF file linked in my sig below, though I don't know if that specific connector is in it, but if you get a part # it might be easier to find online. On larger connectors there is a part # on them but I don't know about that one.

Thank you! I found a pigtail kit, so I think I'm just going to install that. I had my transmission replaced last year and I think that when they dropped the transmission and removed the exhaust, they may have damaged the female connector. The damage is almost right up against the plug, but was covered with conduit so I didn't see it when I was under there this morning.

Here's the pigtail I found on Amazon.

https://a.co/d/00OIU4Ze