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6.4 temp gauge and limp mode

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Old 09-12-2017, 09:22 PM
EvilWrench EvilWrench is offline
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6.4 temp gauge and limp mode

So, I did an oil change, cleaned up the air filter, topped my fluids and closed out a basic service on my '08 F450. Shortly after, I hooked up an 18' bike trailer. Suddenly I had the wrench (service) light coming on. Swung by AutoZone to have them pull any codes. No codes. So the "tech" tells me, it's just trying to say the engine is due for service. Since I already did one, I just need to google resetting the code. OK... haven't gotten around to it. I had a trip to do.

So, I load the trailer, and get headed out. Hit the road and make it less than 10 miles. Suddenly the [water] temp gauge pegs all the way out and kicks me into limp mode. I switch on the defrost as I pull over and do a quick look for leaks and low fluids. Everything is good. The temp drops right back down. Pull out again, make it less than 10 miles and it does it again. Pull over, the temp drops almost instantaneously back to normal, and I can roll again. Every 10 miles... but only with a loaded trailer (not empty). We've hooked up the OBDII multiple times and no codes. The only thing we can come up with is a bad sensor somewhere.

I know similar questions have been posted in the past, has anyone actually narrowed down the exact cause of this BS?
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Old 09-13-2017, 07:24 AM
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speakerfritz speakerfritz is offline
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get a new pressure cap

buy a coolant viscosity tester and check your coolant ratio mix.
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Old 09-13-2017, 09:23 AM
EvilWrench EvilWrench is offline
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Originally Posted by speakerfritz View Post
get a new pressure cap

buy a coolant viscosity tester and check your coolant ratio mix.
We checked coolant specific gravity, we pressure checked the system, we did damn near every troubleshooting step there is... nothing indicates anything wrong. Which is why we're leaning toward a bad sensor.

I have heard about some DPM/DPF issues. So, I'm starting to wonder if that may actually be the problem????
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Old 09-13-2017, 10:09 AM
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I think another possibility is a bad fan clutch. Can you hear it engage?
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Old 09-13-2017, 10:20 AM
EvilWrench EvilWrench is offline
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yes. We checked and double checked everything on standard troubleshooting. With the IR temp gun, the only thing exceeding 200-210 degrees was the turbo (understandable).
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Old 09-14-2017, 11:19 AM
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lookup the codes...a failed number 3 egt will limp and wrench light the truck
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Old 09-14-2017, 06:08 PM
EvilWrench EvilWrench is offline
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lookup the codes...a failed number 3 egt will limp and wrench light the truck
There are no codes. That's part of the problem. Everything "diagnostically" is fine. Temps are good. No codes. Nothing indicates what the problem is.
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Old 09-18-2017, 01:09 PM
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There are no codes. That's part of the problem. Everything "diagnostically" is fine. Temps are good. No codes. Nothing indicates what the problem is.
what tool are you using on the odbc port to scan for codes?????
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Old 09-18-2017, 06:56 PM
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what tool are you using on the odbc port to scan for codes?????
I didn't check really closely. The first time was whatever AutoZone uses. Absolutely no codes. Then, while I was out of town for an interview, a mechanic buddy took it to his shop and ran it through all the diagnostics. I can hit him up, to find out which tool he was using.
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Old 09-18-2017, 10:03 PM
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I'll assume we are talking about the 'yellow wrench', along with a message which displays "power reduced" in the odometer window, is this correct? NOT the "Check Engine" light. If so, you will need to have it connected to IDS to retrieve CMDTCs (Continuous Memory Diagnostic Trouble Codes). A generic OBD II code reader won't read those type of DTCs. By what you describe, it sounds like either P00B7 or P012F has set in continuous memory. Both of those DTCs will put your truck into power derate mode (but P012F should also throw the "Check Engine" light on too). Thermostats are a common failing component to cause P00B7 to set. The replacement is updated. Here is a good youtube video:

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Old 09-18-2017, 10:20 PM
EvilWrench EvilWrench is offline
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Originally Posted by m-chan68 View Post
I'll assume we are talking about the 'yellow wrench', along with a message which displays "power reduced" in the odometer window, is this correct? NOT the "Check Engine" light. If so, you will need to have it connected to IDS to retrieve CMDTCs (Continuous Memory Diagnostic Trouble Codes). A generic OBD II code reader won't read those type of DTCs. By what you describe, it sounds like either P00B7 or P012F has set in continuous memory. Both of those DTCs will put your truck into power derate mode (but P012F should also throw the "Check Engine" light on too). Thermostats are a common failing component to cause P00B7 to set. The replacement is updated. Here is a good youtube video:

https://www.youtube.com/watch?v=_OgTp9xqVtw
Thanks. I'll check into that. Gotta see if I can find a certified FORD mechanic, or someone with an IDS. But my fingers are crossed to get this fixed without sinking a ton of money into it.

I've been hearing horror stories.
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