Troubleshooting help needed, P0117 won't go away.

oddball101 · Oct 20, 2015

My truck is an 01 ranger with an 00 Monty 5.0 swap in it. it has been code free until recently when it started showing a P0117 code (Engine Coolant Temperature sensor, low input), meaning that the the PCM is seeing the motor as having constant temps above 280*.

What I've done:
1. Replaced the ECT sensor with Ford part (didn't know there were different calibration codes for these) after replacing the it first time with an O'Reilly's version that didn't having any bearing on the code either.
2. Replaced the thermostat (motorcraft).
3. Flushed entire coolant system until it ran clean with the little adapter "T" kit from Autozone at the heater core, then ran it to temp, let it cool down again, then flushed it again.
4. Replaced the thin style radiator with a full width one from the JY (I flushed the JY radiator several different ways, effectively showing great flow and no blockages at all.
5. After running a third of a bottle of seafoam through the crank case and driving it around for half a day, I then did a hot oil and filter change using 10w30. I cleared the code, then let it idle to temp and it showed the P0117 as pending again.
6. I've tried tracing out the ECT portion of the harness and cannot find any areas that appear to have any damage. When it goes underneath the thermostat area though, I lose visual and I am not sure where it leads after that. Everything going back up the reverse side into the main harness also seems fine.

The last time the code came up, it was during some "spirited driving" on my way to the JY to pick up parts for my manual conversion (M5R2) that I am getting ready for.. I was excited.

Thoughts:
-I have noticed that lately, when I start the truck, the oil (dummy) gauge jumps back and forth briefly before settling in the middle. The flickering of the needle only occur at startup. Could this be related?
-The code came up when I was 2 hours outside of town and out of desperation, I cleared the code and then put an extra quart of oil in and ran the heater on high heat after that. The code didn't return the entire trip back.
-Could this be indicative of the water pump going bad? I see no signs of leakage and do not hear any odd noises coming from it.

Any help is appreciated..

RonD · Oct 20, 2015

I think the '00/'01 still used 2 coolant temp devices, one for computer(ECT Sensor) and one for the dash board gauge(ECT Sender)

Sender often just used 1 wire but they can also be 2 wire, sensor is always 2 wire
Sender and Sensor were often located next to each other, near thermostat housing.

Not familiar with '00 V8 sensor/sender locations, or what "Monty" means?

Does the dash board gauge show above 1/2 when P0117 happens?

To test ECT sensor:
One ECT sensor wire should have 5volts when key is on, that is the reference voltage used for many devices used by computer, the 5volts comes from computer.
The other wire is the Return voltage, basically a Ground at the computer, if hooked up this wire would show about 3 volts when engine is cold, under 1 volt(.9-.5) when engine is warm.
So very low or no voltage would be P0117.

50/50 coolant with 16psi rad cap will boil at 265degF, so overflow tank would be bubbling if coolant temp actually reached 280degF, did that happen?
If not then faulty sensor, wiring or computer is the cause of P0117.

oddball101 · Oct 20, 2015

Hey, I said Monty in reference to the 2000 Mercury Mountaineer that I used as the donor.

Yes, the Sensor and the Sender are right next to each other. I have not tried swapping out the gauge Sender yet. The temp gauge hasn't hasn't read above halfway at all, even when the check light / code appears.

I have checked the overflow reservoir every time the code has popped up directly after parking the vehicle and there was no boiling. Thank you for stating that. I didn't understand that about the boiling temps for pressurized fluids in the radiator, though I did know to check for boiling as a sign.

I don't have a voltmeter and honestly, I haven't used one outside of minor attempts at learning. However, I may be able to recruit a more experienced friend to assist in testing the voltages.

I cannot find a diagram for how the ECT cables are supposed to be ran, but I am pretty sure I have it the way it was intended..

Still curious if the flickering oil needle may have anything to do with it.

RonD · Oct 20, 2015

Flickering oil needle wouldn't be related.
As you said the Ford Oil gauge is not "real" oil pressure but is run by a switch on the main oil passage from filter to engine.
It is set as below 6psi open, above 6psi closed.
Oil pressure is back pressure not pump pressure, although the pump causes the back pressure.
When engine starts the oil pump pushes oil out thru the filter and into the main passages, when this oil gets to the bearings and other smaller passages it slows down and back pressure is built up at the pump, filter and oil pressure switch, that's what pushes against the diaphragm to close the switch when above 6psi, too much oil

You could have oil leaking back when engine is off so there is a build up then release of pressure causing needle to flicker at startup, or it could be switch's passage/tip is clogged up a bit, or even a failing switch or loose wire on the switch.
The oil pressure gauge and switch use dash board power system, so no relation/connection to computers power system

ECT sensor will have 2 wires on 2000 Mercury 5.0l, Light Green/red stripe and Gray/red stripe
Gray one looks to be the 5volt wire on the diagram, this wire is spliced to TPS(throttle position sensor) wire which also uses 5volts as reference voltage.
Since you are not getting TPS trouble code I would think the 5 volts is OK.

ECT Sender uses 1 wire red/white stripe, this seems to be working since dash board gauge is working.
This is also powered by dash board circuit, so no connection to computer system

Even though you are not actually overheating you do need to fix this issue because computer can shutdown engine if it "thinks" it is overheating.

Have your friend test voltage on Return wire while it is hooked up, test when engine is cold and when warmed up.
You use a sewing pin, needle, to pierce the Light Green/red stripe wire so you can test it while it is connected to the sensor, engine should be off but key needs to be on.
Also test the other wire the same way for the 5volts, above 4.8volts is OK

oddball101 · Oct 20, 2015

Okay, thanks. I will see what I can do and check back most likely tomorrow if not later this evening.

Much appreciated.

oddball101 · Oct 21, 2015

Gr/Rd has no voltage voltage in on position (motor off). PCM pin 38. Has 5 volts.

RonD · Oct 21, 2015

And that is when gray/red is hooked up to ECT sensor?
If so the ECT sensor is bad

One wire needs to have 5 volts
the other wire 3volts(approx) when engine is cold
This is while hooked up to ECT sensor

If the "other" wire has 0 volts then ECT sensor is open(broken), not passing voltage

oddball101 · Oct 21, 2015

Sorry, that previous post was short because I was on lunch and didn't have time to fully edit the response back.

He tested Gr/Rd when hooked up to the sensor with the power in the on position and said there was nothing there. After that, I had him test pin 38 (power on) at the pcm and he was able to find the 5 volts there. So I figure it has to be a short somewhere between the pcm and the sensor. After plugging everything back up though, the check code went away.. and now that I think about it, it's because I cut power to the pcm when I disconnected the wire harness to find the proper pin.

I am considering a jump wire specifically ran between the pcm on pin 38 to the sensor until I can get a chance to remove the upper intake and follow the wires through the part of the harness that lays buried behind and underneath next to the firewall.

You think this is a plausible temporary fix or would this interfere with other sensors as well?

RonD · Oct 21, 2015

You can pull the 5volts from the TPS, should be the top wire but test it.

That wire is suppose to be connected, and share 5volt reference from PCM, with ECT in any case

oddball101 · Oct 21, 2015

I will try to have my friend test again. I don't know why I wouldn't be getting any readings from the wires unless the needles weren't place properly.. I'm at a loss. It just doesn't make sense to me that the sensor is not seeing any voltage at all yet not automatically throwing a code even after the pcm was disconnected from power, when the motor was turned on after. We'll see

oddball101 · Oct 22, 2015

Oh and hey, thanks a lot for helping me like this. I know you don't have to and a lot of people can go unappreciated while others take for granted the kind of help they get on forums.

Instead of bit coins, I wish I could push a virtual beer your way.

RonD · Oct 22, 2015

oddball101 said:
I will try to have my friend test again. I don't know why I wouldn't be getting any readings from the wires unless the needles weren't place properly.. I'm at a loss. It just doesn't make sense to me that the sensor is not seeing any voltage at all yet not automatically throwing a code even after the pcm was disconnected from power, when the motor was turned on after. We'll see

Yes, you would think the PCM check engine light(CEL) wouldn't go out after key was turned on if ECT sensor was open, no voltage.

But unfortunately that could indicate a PCM problem for that circuit.

Thanks for a acknowledgement

oddball101 · Oct 22, 2015

So interesting development. Tested it cold with key on, motor off and it registered at two volts. Let it warm up and tested it again to find only one bolt. He then disconnected the sensor clip and I started to meter needle directly in the gr/rd input (not using the needle) and found 5 volts with motor running. It appears it is getting 5 volts after all..

He checked the other wire and found no voltage at all.

RonD · Oct 22, 2015

Reads like sensors is bad, cold engine, assuming about 70degF should read about 3 volts on return wire, 2 volts would be about 110degF.

Chart here, post #13: http://www.explorerforum.com/forums/showthread.php?t=165007

So engine at 195degF(warmed up) would show about .5 volt

Return wire won't have any voltage when disconnected.

Computer power 5 volts-------------ECT sensor(resistor that changes with heat)------Computer ECT voltage reading circuit---ground

oddball101 · Oct 22, 2015

You wouldn't by chance have a part number, would you? I went to ford and I am using the one the gave me. I bought the sensor from ford after the parts store sensor didn't resolve the p0117 error code. The guy seemed pretty adamant about this being the proper sensor for my truck after going through some hassle about what calibration code my vehicle was set up for. He saw the info on the PCM and was able to trace that back to the proper calibration code I needed and said that the sensor I am using now is the correct one out of like 4.

Troubleshooting help needed, P0117 won't go away.

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