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I have a 2005 Eddie Bauer Explorer, with the 4.6L V8. Recently an intermittent problem developed where the temperature gauge drops all the way below COLD, then a "Check Gauge" light comes on, then about 15 seconds later, the "Check Engine" light comes on. When pulling the code, I get a P0192, which indicates it is in the Cylinder Head Temp Sensor circuit.

I've had the temp sensor replaced twice, the pigtail connector to the sensor replaced, the thermostat replaced and the coolant system flushed, and the problem persists. When I first start the engine, the gauge registers cold (as it should), then will slowly warm up to where it is about half way between cold and hot. It will stay there for anywhere from 1-2 minutes to 30 minutes, then suddenly drop below cold with the lights indicating as stated above. Sometimes, as I drive, it will "recover" and start working normally again, only to drop again a while later.

I am thinking I have a wire that is either intermittently open or shorting between the temp sensor and the PCM that is causing the problem. I had a shop check the instrument cluster, and everything checked out ok. They think it may be the PCM itself, but want a fortune to replace/reprogram it. My though it to first replace the wiring between the sensor and the PCM, but I need to figure out which wire it is on the PCM connector as everything is still wrapped in the wiring harness. Does anyone know where i can get a copy of a wiring diagram for this vehicle? Is there a way to test the PCM before replacing it?
 

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Are you sure it is P0192? That is Fuel Rail Pressure Sensor Circuit Low Input, not Cylinder Head Temp Sensor.

Did you do the thermostat and/or coolant flush before or after this problem started? I'm wondering if there is air in the system.

As far as which wire it is, look at it at the sensor. I don't have a wiring diagram for an '05 but the setup should be able the same as it is for the '98 diagram I do have, at least for this sensor.

On it, a grey/red wire looking like it goes to ground. Whether you have that color or not, you could check both wires for resistance to ground. The other color I see is light green/red and again whether it's that color or not, trace that wire (color) to the PCM.

However if it happens intermittently it can be a lot harder to spot. I'd sooner suspect corrosion in the connector than the wire itself, but only you can inspect the condition of the wires to assess that.

You might also try unplugging, inspecting, and replugging a (couple?) wire harness connectors. One on earlier engines was a big square connector on a bracket on the engine and another was a big rectangular one mounted on the passenger side of the firewall, but again this is for a different engine but yours probably has the signal going through that.

I am doubtful it is the PCM itself for it to work as it is for a good while then seemingly go bad after a temperature rise.
 
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You are correct, code should have read P1289. I'll try testing both wires to ground and disconnecting/reconnecting the other connectors as well. I know they cleaned the temp sensor connector, then subsequently replaced the pigtail from it.
Although the problem is intermittent, it is happening much more frequently (almost constantly), but it does not start happening when the engine is cold in the morning. It starts about the time the engine warms up, then the rest of the day (yesterday was 96 degrees). The problem seems to be worse on hot days, which is why I am suspecting a melted wire or something. It does not seem to be related to vehicle movement. Also, the problem started before the coolant flush and other work. Since it is a dry sensor(in the cylinder head but not reaching coolant) I don't think it is a bubble
 

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You might look around the exhaust manifolds, it's a common area where heat could melt wire insulation though I don't know why it might be routed near that.
 
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