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07-13-2021, 08:59 PM | #1 |
Scooby Newbie
Member#: 284692
Join Date: Jun 2011
Chapter/Region:
SCIC
Location: Carlsbad, CA
Vehicle:2005 STI / Legacy GT Aspen White / Silver |
05 Legacy Gt Rad Fans Constant On (Not Overheating)
Some background: Brand new block with heads reworked. I had the valves lapped and clearances to lobes are spec. New oil pump, water pump, timing belt, headgaskets, brand new engine harness. Im sure there's stuff im forgetting, but it really doesn't matter the engine runs great...
I'll get some other things out of the way to avoid unnecessary posts: *Not the water pump *Not an airbubble *Not a bad thermostat *Brand new coolant temperature sensor *Torque app shows the coolant temp at 240° even when the engine was just started after sitting overnight *Fans turn on and gauge reads hot even before engine is started. (The second line from the top) The engine turns on goes through its normal closed loop operation and thermostat opens (I had to unplug the fans to get it hot enough to open). The engine is running fine and sounds great. The fact that the ecu shows the obd2 app that the coolant temp is 240° (it does not fluctuate not even a half of a degree) makes me think that there could be a ground short after the sensor on the way to the ecu. There was a recall on same year legacy (but in manaul transmission) that stated the fan relay could cause a surge in power and ruin the ecu. My car was not associated with that recall. I also did not have this problem with the old motor. Can a bad relay cause the bad signal to the ecm? Or is the relay only engaged by the ecm after it reads its input from the sensor? Any help is greatly appreciated.
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07-15-2021, 09:50 AM | #2 |
Scooby Newbie
Member#: 400179
Join Date: Aug 2014
Vehicle:2009 wrx |
Is the new coolant temp sensor the only one that has shown this problem? If so, maybe swap it out with a different one.
If the sensor is good, it's probably time to get a dvm and check the wiring from the sensor. |
07-15-2021, 10:32 AM | #3 |
Scooby Specialist
Member#: 29292
Join Date: Nov 2002
Chapter/Region:
SCIC
Location: Orange County CA
Vehicle:2004 WRX wagon silver |
if you are getting aftermarket parts, sometimes they are just not good right out of the box.. you might want to try another just to make sure
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07-15-2021, 11:24 AM | #4 |
Scooby Newbie
Member#: 284692
Join Date: Jun 2011
Chapter/Region:
SCIC
Location: Carlsbad, CA
Vehicle:2005 STI / Legacy GT Aspen White / Silver |
Thanks for the responses.
The coolant temp sensor is new because this was happening with the old one. New sensor same problem. Ive measured resistance between the sensor and the black plug going to the firewall and its continuity is good. The crankshaft position sensor and MAP sensor have continuity on ONE of the coolant temp sensor wires which i am assuming is the power circuit and not a short. Does that sound correct? I can explain better if that doesnt make sense. Thanks again. |
07-15-2021, 12:39 PM | #5 |
Scooby Newbie
Member#: 400179
Join Date: Aug 2014
Vehicle:2009 wrx |
The coolant temp sensor should have 2 wires... one wire that is a signal ground (probably the one that you found continuity with other sensors, so that's probably good).
and the other wire is the signal that goes all the way to the ECU pin C14. Possibly there is a break or a short somewhere between the sensor and the ECU. |
07-15-2021, 01:06 PM | #6 |
Scooby Newbie
Member#: 284692
Join Date: Jun 2011
Chapter/Region:
SCIC
Location: Carlsbad, CA
Vehicle:2005 STI / Legacy GT Aspen White / Silver |
Hey thanks again for the help. I only use genuine subaru parts from the dealer to make sure.
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07-15-2021, 01:11 PM | #7 | |
Scooby Newbie
Member#: 284692
Join Date: Jun 2011
Chapter/Region:
SCIC
Location: Carlsbad, CA
Vehicle:2005 STI / Legacy GT Aspen White / Silver |
Quote:
This is a brand new Genuine Subaru harness Thanks again. |
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07-15-2021, 02:41 PM | #8 |
Scooby Newbie
Member#: 400179
Join Date: Aug 2014
Vehicle:2009 wrx |
with key off, and battery disconnected, disconnect the coolant temp sensor
-can you measure resistance between the 2 contacts in the coolant temp sensor connector (on the sensor itself)? how many ohms? -can you measure resistance between the 2 contacts on the harness side plug? how many ohms? |
07-15-2021, 05:45 PM | #9 |
Scooby Specialist
Member#: 283429
Join Date: May 2011
Chapter/Region:
South East
Location: Down yonder.
Vehicle:2016 Fuji Sunfire 03 Silver |
What does the temp gauge on the dash show?
Unplug the coolant temp sensor. Turn on the key, read coolant temp on ECM it should read -40. Anything else and you have a short to ground, short to power on the coolant temp sensor wiring, or you have swapped the plug with another sensor. |
07-19-2021, 01:40 PM | #10 | |
Scooby Newbie
Member#: 284692
Join Date: Jun 2011
Chapter/Region:
SCIC
Location: Carlsbad, CA
Vehicle:2005 STI / Legacy GT Aspen White / Silver |
Quote:
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07-19-2021, 01:44 PM | #11 | |
Scooby Newbie
Member#: 284692
Join Date: Jun 2011
Chapter/Region:
SCIC
Location: Carlsbad, CA
Vehicle:2005 STI / Legacy GT Aspen White / Silver |
Quote:
The temp on the gauge shows the second line from the top with the engine cold and the ignition turned to on. It shows hot on the ecm at 240 degrees flat with no fluctuation. it does this with the motor cold and off. I cant see where I could have swapped a plug. The only sensors that plug could reach are different connectors. Thanks again to everyone willing to take the time to help. |
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07-19-2021, 01:58 PM | #12 | |
Scooby Newbie
Member#: 400179
Join Date: Aug 2014
Vehicle:2009 wrx |
Quote:
0.9 Ohms is basically a short. But I'm unclear what you were measuring... Was that across the 2 sensor contacts? Or across the 2 harness contacts? |
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07-19-2021, 02:10 PM | #13 |
Scooby Newbie
Member#: 310796
Join Date: Feb 2012
Location: UT
Vehicle:05 obxt |
Just read this thread over on subaruoutback.org. This guys has an NA, but I am pretty sure the coolant sensor is probably the same as the GT/OBXTs. Interesting info on the kind of resistance you should be able to measure there. According to the info the OP reported, the lower the resistance, the higher the reported coolant temp.
I believe heiche is correct there where 0.9 Ohm is essentially a short which would result in maxed out reported coolant temp. --> thread |
07-21-2021, 08:46 PM | #14 | ||
Scooby Newbie
Member#: 284692
Join Date: Jun 2011
Chapter/Region:
SCIC
Location: Carlsbad, CA
Vehicle:2005 STI / Legacy GT Aspen White / Silver |
Quote:
Quote:
Trouble now is I am getting a p0459 EVAP Purge Solenoid Voltage High. I think I may have damaged the solenoid or ECM by swapping the plugs. I still dont believe its the brand new harness because continuity is good from the black firewall plug to the sensor plug. There is a guy on ebay that sells a solder kit to fix the ECM because I guess it is common for the ECM to burn and cause that code (probably from people like me swapping the plugs on accident). I am going to start with testing the solenoid on a bench. Thanks again. |
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07-21-2021, 08:57 PM | #15 | |
Scooby Newbie
Member#: 284692
Join Date: Jun 2011
Chapter/Region:
SCIC
Location: Carlsbad, CA
Vehicle:2005 STI / Legacy GT Aspen White / Silver |
Quote:
Thanks again for input |
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07-22-2021, 09:14 AM | #16 |
Scooby Newbie
Member#: 310796
Join Date: Feb 2012
Location: UT
Vehicle:05 obxt |
OK. You are getting closer to fixing your issue then.
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