Coolant temperature
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Elder User
Joined: Sep 2012
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From: Smokey Mountains TN
Coolant temperature
hopefully you guys can help me . PO of my truck put in a manual gauge for coolant temp. Now just the other day my torque Converter was no longer working .
after scan , I discovered the converter is not getting a signal due to “overheating” . The PCM thinks my engine is at 305 degrees ... checked with two different scanners. As far as I can tell , there is no short in the coolant wire , I tried a new sensor , still high temp . Glow plugs and exhaust gas valve work as normal .
any idea where to check an why I get that high of a coolant temp ? Thanks a lot
after scan , I discovered the converter is not getting a signal due to “overheating” . The PCM thinks my engine is at 305 degrees ... checked with two different scanners. As far as I can tell , there is no short in the coolant wire , I tried a new sensor , still high temp . Glow plugs and exhaust gas valve work as normal .
any idea where to check an why I get that high of a coolant temp ? Thanks a lot
Postmaster
Joined: Sep 2007
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From: Medford Oregon
PCM does not monitor engine coolant temp ever, it's a gauge display only. PCM only sees EOT and and with the automatic transmission TFT.. If the EOT was up to 305* you would have other issues and the water overheat light on the dash would be illuminated.. Usual issues with transmission not working properly is a bad brake light, in this case. If you can scan actual EOT that would help narrow down the issue on temps.
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Elder User
Joined: Sep 2012
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From: Smokey Mountains TN
If the coolant temp is not reported to the pcm, why can I read it with a&e and also another software?
per ( old school) transmission shop, a high engine temp prevents the TC to engage ...
my regular brake lights work, but I believe my 3rd light is out .. Cruise works.
feeling confused :-)
per ( old school) transmission shop, a high engine temp prevents the TC to engage ...
my regular brake lights work, but I believe my 3rd light is out .. Cruise works.
feeling confused :-)
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Joined: Apr 2016
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From: Bahstun
PCM cant read coolant temp. What PID are you using?
Third brake light does weird things to trans if its burnt out or using LED with out resistor.
There is an air temp sensor that you might be reading
Third brake light does weird things to trans if its burnt out or using LED with out resistor.
There is an air temp sensor that you might be reading
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Elder User
Joined: Sep 2012
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From: Smokey Mountains TN
From what I found online is that a&e as well some other softwares getting bogus info on the coolant temp , as it is not reported to the PCM as mentioned before.
So, that would rule out the issue of temp. Now I got to find out, why the PCM is not sending a Lock signal to the TC.
cruise works, speedometer works,... brake controller and trailer wiring works flawless while pulling 3 weeks ago. ...
any thoughts on where to hunt ? I will check/ fix third brake light if it’s broke .. don’t think it ever worked though ...
So, that would rule out the issue of temp. Now I got to find out, why the PCM is not sending a Lock signal to the TC.
cruise works, speedometer works,... brake controller and trailer wiring works flawless while pulling 3 weeks ago. ...
any thoughts on where to hunt ? I will check/ fix third brake light if it’s broke .. don’t think it ever worked though ...
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Postmaster
Joined: Sep 2007
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From: Medford Oregon
If cruise control works then brake lights are not the problem, IMO. On mine if cruise set it would engage then disengage thinking I was pushing on the brake peddle. Ended up being a burnt out brake light bulb at rear, a common symptom of burnt out bulbs. That's why we ask about the 3rd brake light up top. Also noticed when coasting to a off ramp TC would unlock quicker, like I was pressing on the brake peddle. Some later PCM's had code modifications to prevent this from happening, so I've read. My 97 build date is December 97 and it still does it but only if a rear brake light burns out, go figure. My third brake light had been our for years so maybe it takes two brakes light bulbs to go out, one up top and one in the rear before the PCM will detect the problem with newest 97 software, which I have.
PCM supplies a small voltage, I think around 3 volts to the brake circuit, green wire, you can actually measure it. It monitors this voltage and of course if you step on the brake it goes up to 12 volts. Since all brake bulbs are in parallel if one burns out the resistances of the filaments goes up and creates a larger voltage to the PCM and it is thinking you have stepped on the brake. Why ford used this strategy on brake detection I have no idea. This is why installing LED brake lights are a problem as they don't have the current load necessary to keep the PCM happy. As long as the LED brake lights have the necessary load resistor internal to the LED assembly or ones installed external to the LED assembly all is OK.
Not indicating you have LED brake lights, just some information for those thinking about installing them and what issues could occur if not done properly..
Yes, if you look at the diagrams there is no physical wire from coolant sensor to the PCM. As you indicated the number are bogus, some scanners will show just dashes or nothing at all.
PCM supplies a small voltage, I think around 3 volts to the brake circuit, green wire, you can actually measure it. It monitors this voltage and of course if you step on the brake it goes up to 12 volts. Since all brake bulbs are in parallel if one burns out the resistances of the filaments goes up and creates a larger voltage to the PCM and it is thinking you have stepped on the brake. Why ford used this strategy on brake detection I have no idea. This is why installing LED brake lights are a problem as they don't have the current load necessary to keep the PCM happy. As long as the LED brake lights have the necessary load resistor internal to the LED assembly or ones installed external to the LED assembly all is OK.
Not indicating you have LED brake lights, just some information for those thinking about installing them and what issues could occur if not done properly..
Yes, if you look at the diagrams there is no physical wire from coolant sensor to the PCM. As you indicated the number are bogus, some scanners will show just dashes or nothing at all.
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Thread Starter
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Elder User
Joined: Sep 2012
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From: Smokey Mountains TN
Thank you. That’s some good info . I do not have any LED lights . I will check to ensure all lights are working and double check the cruise on my way home.
one thing I had not done yet, is unplug the programmer to see if it messed up.
if not that .. what other factors would prevent the PCM from sending a lock signal?
one thing I had not done yet, is unplug the programmer to see if it messed up.
if not that .. what other factors would prevent the PCM from sending a lock signal?
Postmaster
Joined: Sep 2007
Posts: 4,195
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From: Medford Oregon
I'm assuming this is a new issue and something not going on for years?
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Elder User
Joined: Sep 2012
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From: Smokey Mountains TN
Last nite I run a jumper from below the brake booster to a switch to ground.. Did not work. Transmission temp works. Today I will check continuity down to the transmission plug, just to make sure.. but it appears to be now an issue inside the transmission. I checked and the torque convert is dry and does not show any signs of ever getting too hot,
oh and I do live in the east Tennessee mountains now, with very low temperatures at the moment :-)
oh and I do live in the east Tennessee mountains now, with very low temperatures at the moment :-)
Postmaster
Joined: Sep 2007
Posts: 4,195
Likes: 6
From: Medford Oregon
Here is a good reading thread and sounds similar to your issue.
https://www.ford-trucks.com/forums/1...-no-codes.html
I'm assuming you have no codes thrown regarding the transmission. What puzzles me if why AE doesn't report the command to lockup. I've looked and can't find transmission solenoids resistance valves in my library but sure they out there somewhere.
https://www.ford-trucks.com/forums/1...-no-codes.html
I'm assuming you have no codes thrown regarding the transmission. What puzzles me if why AE doesn't report the command to lockup. I've looked and can't find transmission solenoids resistance valves in my library but sure they out there somewhere.