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tamaz
tamaz, Subaru master technician
Category: Subaru
Satisfied Customers: 1203
Experience:  Subaru certified,ASE Master technician,25 years experience
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O/H an 03 Forester. Heads were warped & owner filled eng

Customer Question

O/H an 03 Forester. Heads were warped & owner filled eng with stop leak. Boiled out 3x to get everything clean. Put rblt eng back in car and found neither cooling fan working. Checked all fans, fuses, temp switch, & relays... all good. No gnds cmg from ecu. Verified wiring to and from is good. Swapped in known good ecu, no change. What the heck?
Submitted: 1 year ago.
Category: Subaru
Customer: replied 1 year ago.
Verified coolant temp switch (sensor) is in proper parameters relating temp to resistance as per chart. Grounds cleaned and checked
Customer: replied 1 year ago.
I know ecu logic for fans changes at 6 mph. I am wondering if (auto) trans module is giving a false signal and if so how to check and or verify. I am guessing owner had cooling fan failure, boiled over, warped heads then tried to fix problem with about 3 cans of stop leak.. this thing was a mess. BTW thermostat new and parameters checked, antifreeze filled with my vacuum machine so no air pockets, radiator cleaned and flow checked, hoses are good. New rings, bearings, pistons,waterpump, timing belt, tensioner idlers, crank position sensor, six star head gaskets, valve job with heads milled (still within limits, new plugs & wires, injectors cleaned, no exhaust in coolant. Verified ecu getting correct temp signal. Had car at over 200+ degrees before I manually overrode fans to cool down
Expert:  Matt replied 1 year ago.

hello

1st thing to try is does the fan work when you give it 12V?

as they can seize up or fail internally

Customer: replied 1 year ago.
I said all checks out back to ecu. If I remember correctly it is something like pins 13 & 14 on plug b137... not near my paperwork right now. By taking these to gnd alone or together I can get all fan speeds thru fan relays 1 and 2 and fan mode relay. The A/C relay is also not coming on but can be activated by grounding the actuation coil. Problem appears to originate at ECU. Swapping to another car and all is fine... take other ECU and put it in this car and no fans. Was hoping someone has seen this at their shop. I don't have a logic diagram of ECU but it appears ECU is looking for something it is not getting, that is why I wonder about the trans module input.
Customer: replied 1 year ago.
I am factory trained on VW, Audi, Porsche, and Jaguar. I was a heavy jet ( B767, B767, etc) mech and now retired. I hold every lic you can have for working aircraft including airframes, powerplants, avionics, radar left seat qualified etc. I do this on the side now... never thought a lowly Subaru would kick my a__.
Customer: replied 1 year ago.
In my first posting I mentioned fans, fuses, relays etc all checked good. That is why I was able to over ride sys by grounding ecu wires going to relays ( fans will work as should). That also checks the wires and continuity (no shorts or opens). I did ring out related wiring tho... no problems. That is why I am hoping you might have access to or experience with what is needed to correct situation. I have tried to give you as much info as possible hoping "another set of eyes" is what is needed. Solve this and I will go above the $24 because this will save me shop time.
Expert:  Matt replied 1 year ago.

hello

you've done a lot of the normal background tests I'd reccommend

so I'm to open this back up to other experts one of whom hopefully has seen this before

good luck

and don't reply to me, please wait for the next expert to pitch in

Expert:  tamaz replied 1 year ago.

Hi,this sounds like a interesting problem.From your notes(which are very detailed) you've done quite a bit.Let me ask if I may if the cooling fans come on with when a/c or defrost is selected unless I over looked it I did not see this in your notes.How are you monitoring engine temperature?scanner?What temperature thermostat is installed,thanks for your time,I'll do my best to help you out here.

Customer: replied 1 year ago.
Subaru thermostat... starts to open at 78 degrees C fully open at 90 degrees C. A/C currently inop (owner didn't want it fixed) sys is depleted (leak?) compressor was disconnected. Green light comes on on console but no power probably low press sw. I have a scanner thru the OBD2 port able to read eng codes, reset, and check eng parameters in real time operating mode. Grounding pins 13 and or 14 at ecu plug b137 makes fans work. I grounded them while disconnected from ecu to avoid inducing a new problem. Thanks for trying to help
Customer: replied 1 year ago.
Coolant temp sw (sensor) 2.52 kilo ohms @ 70 degrees. Followed chart perfectly thru warm up. Gauge on dash read approximately the same. This car has just the one three wire sensor serving both
Expert:  tamaz replied 1 year ago.

So,the car doesn't overheat now, right?My question is when do you think fans should be coming on,they should come on about 204-209,has the engine temp ever reached beyond this?What does the gauge show ?Sorry about all the questions but the more info I have the easier it is to wrap my head around it,thanks

Customer: replied 1 year ago.
Believe fans should be on low 203 to 210 degrees F... 212 and above high. Have taken to 215-220 no fans. Manually over rode to cool down. Gauge was in red. Don't want to warp anything so used shop fan and over ride on fans to cool down while running (not just shutting eng down and letting it cook)
Customer: replied 1 year ago.
Thinking of trying to bridge and or bypass A/C sys so ecu thinks it is operating. Really running out of ideas. Would even think about flashing and reprogram of ecu but this works fine in a different car and that cars ecu has the same problem in this car. Yes, correct p/n ecu is being used
Expert:  tamaz replied 1 year ago.

Yep ,temps are at the range that fans should begin working,for giggles did you think about replacing coolant temp sensor to be honest although the values are matching up what else would command the fans to come on, plus having overheating could have damaged it also.

Expert:  tamaz replied 1 year ago.

Hi again,the coolant temp sensor must be delevering the engine temp since your reading it through your scanner, sorry I hate parts changing anyways.I'd like for you to do me a favor and put the electrical system into diagnostic mode ,this will run all solenoids relays fuel pump and cooling fans on high and low speeds ,to place in this mode there are a set of green connectors under the dash that need to be plugged together to place in this mode.The connectors reside on the drivers side above the foot well depending on the build date these connectors are either to the left or right of the steering column.When you find them connect them and turn key to on allI mentioned should run on/off continuously until key is turned off,let me know if fans are operating,thanks

Customer: replied 1 year ago.
I was aware of that and never thought about trying that. Will try first thing in morn when I get to shop. Yeah, thought about changing the coolant temp sensor but all readings are textbook thru ecu plus using the chart to plot the inverse relationship of temp to resistance made me decide it would be a waste of time and money. Will advise tomorrow as to the diagnostic mode test. I am expecting it to test ok... because I think the ecu logic is looking for something it is not getting ie. Speed sensor feed from trans module or even possibly the broken A/C systems control module. Thank you and have a good night, talk to you tomorrow
Expert:  tamaz replied 1 year ago.

thanks,goodnight

Customer: replied 1 year ago.
As suspected relays and fans did activate. Still left with why they are not working when they are supposed to. May just bite the bullet and change the coolant temp sensor. Doesn'T make any sense but running out of ideas. Test drove today... temp stayed about midway. When I idled in parking lot it tried to overheat. Suggestions greatly appreciated...
Expert:  tamaz replied 1 year ago.

Hi,this is boggling.I'll take a bite out of that bullet too ,try the temp sensor. I did a little research on the ECM logic and could not find anything about the logic concerning the speed signal but I was thinking about the seat belt warning light. Are you aware if your belt isn't buckled if the warning light flashes and audible tone sounds after moving more than 6mph? Not sure if this isn't working if it would cause fans not to operate... just a thought,I will talk to you tomorrow, thanks.

Customer: replied 1 year ago.
Found a chart breaking down speed in relation to cooling fans. It even shows differences between cars with factory a/c and cars with out (veh speeds are monitored in 4 steps and each step references, fan 1 low, high, or off/ fan 2 low, high, or off/ all fans off) Fans are related to speeds and a/c loads. If interested I could forward chart for your reference in case you ever run into this. I believe I found it's signal wire but don't know what its parameters should be. You don't have access to an ecu logic diagram, the type with and gates/ or gates/ nand gates, etc. You should see what they look like on a Boeing 767 and 747, and when they have problems everybody is standing behind you asking..."are you done yet, are you done yet?"
Expert:  tamaz replied 1 year ago.

Hi,if you can forward the chart to me I'd be interested to see it.Have you changed out coolant temp sensor yet?I'm curious,thanks

Customer: replied 1 year ago.
Not changed yet. Car came into shop needing immed. attention. Probably will get changed Monday
Customer: replied 1 year ago.
This should be the image... if it doesn'T work let me know and I will send a different way
Expert:  tamaz replied 1 year ago.

Thanks!