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02 F-150 Extended Cab
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2,610 Posts
Discussion Starter · #1 ·
I keep getting a code for a coolant temp sensor malfunction (P0115). I replaced the sensor with a new one and all was good for like maybe 250-300 miles then all the sudden it came back one night and my car wouldnt even start and it was running pig rich!

Wiring is good and it checks good on the voltage meter..no quirks in the voltage if i move the wires around. Help!
 

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Mobile Diagnosis Guy
97 Impreza L
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5,492 Posts
if it was running pig rich it is because the sensor is either reading -40* (bottom line of most ECTs) or the sensor is unplugged and not reading or the wires are severed somewhere.
 

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02 F-150 Extended Cab
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Discussion Starter · #3 ·
it just ran pig rich at start upand it was idling kind of funny, but that was probably due to the fact i kept cranking it and the cylinders probably got loaded up with fuel.

the wires cant be severed because i checked the ECT circuit with an ohm meter and it shows current flowing through it so... ^_^_^

perhaps there is a fray in it somewhere. hMM.
 

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Mobile Diagnosis Guy
97 Impreza L
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5,492 Posts
just check the ECT voltage at the ECU, it should be around 3.5v this time of year when the car is "cold" then drop to like 1v when the car is warmed up.
 

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02 F-150 Extended Cab
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2,610 Posts
Discussion Starter · #5 ·
how would i go about doing that, probing the back part of the connector where it plugs in?
 

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02 F-150 Extended Cab
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Discussion Starter · #6 ·
COuld this possibly have anything to do with my rear o2 sensor being bad? or my front o2 sensor?

i have a invidia d/p with a CEL fix (2 sparkplug anti-foulers) no cels for that anymore but..could it affect the ect?
 

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Premium Member
2005 STI , 1998 Outback Sport
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206 Posts
Your downstream o2 sensor will not affect engine performance. Its only there to see if your cat is working. Do you know anyone that has a good scan tool that gives data streams? Thats the easiest way to figure out whats wrong. Dont rule out the fact however that it could be a bad sensor. That happens more then you think. Especially if it is aftermarket.
 

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2,610 Posts
Discussion Starter · #8 ·
I ohm'd both sensors, they check out the same so i really doubt its the sensor. the down stream o2 does affect fuel trims but i guess it is irrevelent to my problem atm.

hmna'
 

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Discussion Starter · #11 ·
for realz? you check that voltage at the ECU?
heh not yet. the new sensor seems to be malfunctioning intermittingly, as it works then it goes back to throwing the code.

i have a spare ej22e block in the basement so i decided to take the ECT out of that and put it on. so far so good....so far...:crazy:
 

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I know this is 2 yrs old but i just rebuilt my ej18 and its throwing the same code (p0115). Did the new sensor fix the problem? My idle is pretty high (2500rpm!!) is this because of that problem? And the cooling fans still come on when they should and the temp. gauge is accurate.
 
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