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George H.
George H., ASE Certified Technician
Category: Car
Satisfied Customers: 18701
Experience:  ASE Master Tech 15+ yrs, AAS Automotive Technology, Factory trained Asian specialist
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2002 Hyundai Sonata: 4cyl..the TCM relay located

Resolved Question:

what causes the transmission code "TCM relay always on". the car is a 2002 Hyundai Sonata 4cyl auto. . were is the TCM relay located?
Submitted: 8 years ago.
Category: Car
Expert:  George H. replied 8 years ago.

Hello I will help you with your question,


The relay is located behind the radio/HVAC stack. There are two causes possible for this code, one the relay is really stuck on, the other is the harness is frayed in the transmission valve body. There is a TSB regarding this code.


If the fuse is blown for the trans controller (fuse #6) the harness in the trans is likely shorting. Check this first.






The harness rubs through on the detent spring


Let me know if you have questions


Thank you

Customer: replied 8 years ago.
all the fuses under the hood are good. The car is a Elantra not a sonata is it still in the same location? Could the harness fray and not blow the fuse?
Expert:  George H. replied 8 years ago.

The Elantra is a whole different animal.


If you have a relay stuck code (P1723, P0885) and the #1 fuse is good replace the control relay then check the wiring between the transmission and the transmission control module for opens or shorts, fraying or melting.






The relay is next to the TCM and near the brake pedal. The junctions in the fuse block may have intermittant faults, monition the voltage at the relay with a test light to be sure the light does not flicker at any time. The light should turn on and off with the key and steady

Customer: replied 8 years ago.
<p>Sorry about that. I found the relay today beside the tcm (wish I woulda had that picture,lol). The red wire has power and doesnt flicker . All fuses are good. I thought maybe unplugging the relay would keep the code from coming on but It didnt. I cleared it then unplugged the relay and as soon as I started the car, it came on (with the relay unplugged).</p><p> Does one particular driver on the TCM go to the transmission? !, 2 or3? I orderd a relay even though the parts guy at the dealer said they never sold one (theyve been known to bullshit people from time to time)</p><p> ;                                        Thanks</p>
Expert:  George H. replied 8 years ago.

This is why I went to the trans harness when you first posted. I have had 20-30 of these in sonotas but it was the harness not the relay. I have had 2 in 10 years that were the relay. The code will set if the TCM does not see the change of state on the two B+ inputs to the TCM when the relay is commanded on. Here is the wiring diagram so you can follow along




The other possibility is the harness in the trans but you should be able to test from the pin #9 and #10 in the trans connector to the case of the trans to see if the harness is shorted there. The joint connector C92 in this picture is a suspect also





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