So I've had this issue for a while and have been slowly trying to fix it but nothing seems to be working. My trucks oil temperature will rise to operating temperature and then will fall to 130-operating temp. It's erratic. When it does usually in short order the fan comes on. Though lately once I jump on the freeway at operating temp the fan throttles up. It's throwing p0198 every time the fan comes on either the light code (grey) or usually the yellow or red. My gauges (torque pro nor dash) ever get above 200*. I have replace oil temperature sensor and pigtail. I have put in a new engine wiring harness from all those sensors to the pcm. I have also removed the programmer (edge) that intercepted the harness before it went to the pcm and I just drove her to work and it happened again. Do I need a pcm? I just don't know now where else to go nor how to test If it is my pcm as that's what's next in line. I don't wanna keep throwing parts at it. Thanks for any help.

 

Someone here may have a PCM to borrow, Yahico may know of one for you to try instead of throwing money at the problem.

 

That would be ideal. I'm wondering if getting an sct and Re-flashing the truck would help. I'm in Pinellas park, FL if someone could help I'd drive to them.

 

I also have the snap on scanner if I can check the pcm with that...I guess I'll toy around with it after work.

 

So I just hooked up the scanner and during an engine running self test it pulled the p1703 code. It says Brake On/Off Switch Out of Self-Test Range. I have no issues with my brakes though I'm wondering if that code could have something to do with my issue?? Idk again any help is appreciated I'm gonna try and dig in a bit tomorrow into that code anyway so hopefully I get somewhere.

 

Since electrical is not my thing I have someone coming over. Can you fill in all the details or history on the truck of what has been repaired. If you went Gator hunting and swamped it, these are good things to know...

 

lol ya I gotcha...no never swamped it. So I've had it almost a year, started with new oil, coolant flush filter and change, fuel filters, oil cooler, egr delete, degas bottle replacement, I put in gauges, high idle switch, new radiator, new water pump, update hfcm drain, blue spring which led to new oil filter and secondary fuel filter housing 😒, new oil and filters in the trans, I did clean the egr valve at some point, I just changed the harness due to this issue and removed the edge programmer it had on it from when I bought it. Now details on what happens...everything is normal if there are no codes present at start. Once to operating temp, or on the freeway the fan ramps up, now sometimes it comes on when I first start the truck as well. Oil temp and coolant temp will be in range and coolant temp never gets above 194. Oil temp will get to temperature (190* ish) then drop to 170 or 130 or anything in between. What I think is happening is a quick rise in "temperature" on the sensor that causes the fan to kick on. Now if I secure the truck clear the code p0198 grey, yellow, or red the fan will remain on for a while even if the truck is cold. Now if it doesn't throw a code the fan will remain on longer again with no temperature cause. I never see any gauges (torque pro) over 200* even on the highway. My dash gauges ( I know their useless) never move ( of course). So the harness is new to the truck and I went through it before install. The sensor is new as is the pigtail. I'm at a loss.

 

When you got the P1703 did you cycle the brakes when asked?

Now onto the P0198.
Do you have a way to watch the Vref voltage? Should be very stable 5.00 VDC
± just a tiny fraction. The P0198 is telling me that the temp reading wire is OPEN
or SHORTED to Vref.

Do you have the EBP sensor (Exhaust Back Pressure) on this engine? Take a very close
look at the connector of this to see if you have a damaged wire.
Then have a look at the fan connector and check it for any damage on both sides of
the connector.

One thing I would like you to try is unplug the fan connector and go for a short drive.
Keep an eye on the temps. If they just then just plug the connector back in.

Last thing to try. Unplug the EGR valve and see what happens. It will make the truck a bit upset.

I am going to have to do some reading tonight. Let me know if you find anything with
the steps I asked you to try. The Vref being the most important one. It goes all over
the truck.

 

Sean - Ford's spec on the v-ref seems to be 4.5 to 5.5 IIRC.

In your opinion, is that too wide a range?

 

±0.5 VDC is really not too bad.
I bet you more often see between 4.80 to 5.20 if not right a 5.00

The thing to really look for is stability. If the Vref is bouncing all
over the place. Then there is something going on like a bad voltage
regulator, heavy load or a short

 

Where did the new sensor come from, Ford or the local auto parts store?

 

I got it from dieseltruckpartsdirect.com so not ford but it is a Siemens sensor. And thank you for the response I did the vref this morning into work and it dropped to 0.0 twice that I saw as I was driving I'm sure I missed the first one cause the fan had already come on. So I'm assuming that's not good. I will do the rest of the checks today once I get off work. Thanks again for the response it really helps to have some guide as to where to look.

 

Also I do have ebp I will check it and my wire from pcm to the sensor is new as is the sensor...like I changed not only the pigtail but the entire harness from the pcm.

 

oh and yes I did pump the brakes and it caused the engine to run like **** and the test to stop throwing that code

 

ok drove home from work with the fan unplugged. No overheat code nor crazy gauge movement. I unplugged the egr (fan plugged in) and drove a bit and the truck didn't care but the gauge was super inaccurate and all over the place. Gonna put a meter on the fan wires itself. The looked fine but we'll see what fluke says about that. Oh and I get a p1000 every time I check codes dunno if that matters.