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Flashing AT OIL Temp Light

4160 Views 7 Replies 2 Participants Last post by  Titter
ok so my problem is a little different than all of the "flashing oil temp" threads that i have alreday searched for.

so what i have is a JDM GDB-E EJ207 in a 2002 USDM WRX mated to a 4EAT Automatic using an ECU from a JDM 5MT Forester SG5.

my AT Oil Temp is flashing and we pulled the code and its my ATF Temp Sensor. code#27 "ATF Temp Sensor. Detects open or shorted input signal circuit"'

what seems to be the problem is i think the manual ecu isnt accepting the fact that there is an AT Temp Light and its just signaling that there is a problem. manual cars dont have a TCM, but there is obvious communication from the manual ECU to the TCM or else it wouldnt work in the first place. i have the pinouts for the TCM, but i'll admit electrical is not my strong point. aside checking voltage and continutiy, i dont really know what to look for.

the car runs completely fine, no issues what so ever (except this blinking light of course). its been running for well over a year. trans temps are fine and stuff. it shifts fine. its just a constant blinking light on the dash that is really really annoying and i feel its time to try to figure out this problem.

so knowing what the problem is... does anyone have any clue what i can do? i mean i can pull the bulb or do something to the cluster but that is a last resort. i was hoping to find an actual electrical solution. even something like deleting the code from the TCM like you can delete codes in the ECU.

(please no 6 speed comments. this is the route i have chosen for multiple reasons i do not what to clutter this thread up with)
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I could go into a long winded plan to do what you are looking for. But,,,,,, you will be chasing your tail. Lots of hunting and reading schematics for proper voltages and wires. And then if you do get it to work, I suspect you will just get a "different" error code something like "ATF not at proper temp" since the ECU is not looking for this information yet the TCM is trying to send it, resulting in an error code, just like the no input error issue. I suspect the error codes pass from the TCM to ECU but not some of the actual sensor signals inputs/outputs. Not much you can do except block/pop the bulb and hope you don't have a REAL transmission temperature problem. I think if it were me, I 'd be looking for a proper ECU..............
its not the ECU thats the problem. i should have mentioned there is no CEL. the car is properly tuned and the ECU works fine. its most defintely a TCM issue. AVCS is wired and functioning properly thats why im not using the AT USDM ECU that originally came with the car. any 16bit JDM Ecu with AVCS control flashed with the proper ROM Cal ID will function with custom tuning. using a JDM v9 STI Spec-C ECU that matches the motor will not resolve the issue (as i have tried that already)

also forgot to mention i have an external temp gauge to monitor my temps as well as an external cooler.
-ATF temperature sensor (+) (B55) No. 23 (-) (B55) No. 12 (V) 3.5-4.3 (Ohm) 2.5k -7.0k
-ATF temperature sensor ground (+) (B55) No. 12 (-) (Chassis Ground) (V) 1.0-2.2 (Ohm) 300-800

this is the info from the diagnostic manual for the TCU.

as you said pulling the bulb wouldnt let me know if there are any other problems as the flashing is used to signal a TCU error code.

with the information from the diagnostic manual... is there a way to make a bypass similar to other resistor mods?
Yep I was confused. I do not believe the ECU (or ECM, the engine control unit or module) has much,if anything, to do with the TCU/TCM. I see in my schematics the TCM talks to the BIU (body integrated unit, but not the engine controller. Soooooooooo, you are correct it is a TCM issue. The TCM is not sending the proper voltage (should be 5V) to that sensor. You either have a bad TCM or the sensor (or wires to it) itself is bad. Have you tried replacing the sensor itself or checking for 5V at one of the wires to it?

Should say I am looking at 2015 schematics and assuming the arrangement is "similar."
the transmission is about to be overhauled with IPT internals. will definitely check if the sensor is fauly in anyways during that, but wont be for another week or two. the sensor is in the valve body so its not a simple procedure to inspect it.

in the mean time im reading something about an AT/MT indentification pin on the ecu? when swapping from AT to MT older subarus you need to change the AT/MT ID Pin on the ecu and add a ground. but i cant seem to confim if this needs to be done on my ecu's. the swap was over a year ago and i honestly forget if it was done. but i figure if it was not done then i would have alot of other problems no? since i am technically an AT on an MT ECU i would need to do the process in reverse?
Sorry, can't help you there. But I do think the trans temperature light blinking has nothing to do with the ECU (assuming ECU is the engine controller in your car.)
ok cool ty. appreciate the time & info you have shared :)
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