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Falsely overheated

pcb

The Diagram Dude
:
2002 MP5
If I were you, I'd put that orange wire back where it came from in the connector then string some of your white wire from it all the way to the orange wire of your sensor and spice it in and see if your temp gauge starts working.
 

pcb

The Diagram Dude
:
2002 MP5
Just browsed the schematic; that orange wire is the ground return for all sensors, that we agree on. If that wire was not making to the ECU plug then a whole load of other sensors wouldn't work and the car would -maybe- not even run at all.
I'm pretty sure that is the case.
Her car spontaneously died so the O2 sensors, throttle position sensor and transmission fluid temp sensor may all have failed.
 

pcb

The Diagram Dude
:
2002 MP5
What the OP needs to do is verify that the Violet/Yellow wire is making it to the ECU [pin 38]. Easiest way is to measure [with the ohmmeter setting] between pins 38 and 91 of the ECM connector. It should read SOME resistance, -the sensor's resistance. If open circuit THEN follow wires.
The ECU feeds a positive voltage out on the Violet/Yellow where it goes to the temperature sensor and the temp gauge.

If there is no ground path (orange wire) the voltage would remain high and the gauge would read maximum.

The OP had a mechanic measure the voltage at the temperature sensor and it was way too high.



 

pcb

The Diagram Dude
:
2002 MP5
... i had a mechanic come out and look at it and tested the engine coolant temp sensor to find out that was giving off almost 3x the power it need. so i replaced that, also tried to replace the clip for it with new wires and no luck. the mechanic told me i need to trace back the wires to the harness and see where it’s burnt out at and go from there.

Tracing back the wires through the harness is a pain in the ass.

You know which wire is "burnt" and where it starts and the five places it finishes.

Just stringing a new wire is a lot easier even if you have to tap into all the sensors and their orange wires.
 
I connected the white wire to the sensor and the ECU just to see if it would change anything before i replaced the whole wire. and that still didn’t do anything.
 

pcb

The Diagram Dude
:
2002 MP5
So the white wire is going from the orange wire of the sensor to pin #91 at the ECU?
And you hooked your battery up?

And your ECU connector is plugged in to the ECU?
 

pcb

The Diagram Dude
:
2002 MP5
Damn...

Are you sure you spliced into the orange wire?
I guess the sensor itself has black wires until it gets to the connector?

Try disconnecting the half of the wire that you spliced into that leads into the harness so that the white wire only goes from the ECU to the orange wire of the sensor.

Perhaps the orange wire is shorted to ground somewhere and that's messing things up?

So, the white wire going straight from pin #91 to the orange wire that has been cut out of the circuit.

(That won't help the other sensors but see if you can get the temp gauge working)
 

pcb

The Diagram Dude
:
2002 MP5
The only other thing I can think of is a bad connection on pin #91 or a bad ECU.

Check the pin on the ECU that goes to the orange wire to see if it's bent, broken, dirty, loose or something.
 

pcb

The Diagram Dude
:
2002 MP5
You might get lucky and all the sensors can feed through that wire.

It depends on where the "burnt" wire is and if all the orange wires are on the same side of the burnt spot.
 

pcb

The Diagram Dude
:
2002 MP5
Try wiggling the orange wire at the ECU while watching the gauge.

I think your still on the right track.
 

pcb

The Diagram Dude
:
2002 MP5
Maybe try removing that orange wire from the connector again and plug it directly onto the pin of the ECU to see if its snug or sloppy.
 
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