2003 Hyundai Elantra "engine light" is P1723: is the problem more likely the RELAY SWITCH or the SPEED SENSOR?

Question

I own a 2003 Hyundai Elantra (9+ years old, 99,000 miles). When very cold, the transmission "bucks" into REVERSE gear and also bucks (to a lesser degree) when moving to DRIVE; the power is also extremely low. The Engine Check Light (P1723) indicates either a Transmission Relay Switch or the pair of Speed Sensors (Pulse Generators). After about 10 minutes, the light goes off and the cars run PERFECTLY. This has reoccured about 5 times now; and only (so far) when the engine is stone cold and the outside weather is less than 20 degrees.

I have to "gamble" and fix either Transmission Relay or Speed Sensor". I am leaning towards Transmission Relay. Another P-Code (P0715) seems to be more attuned to the Speed Sensors: this problem seems to cause the Transmission to drop to 4th or 3rd gear while the car is in motion.

Based on my description, Which problem is more likely: Relay or Speed Sensor?

Thank You

Answer 1

P0723 Output shaft speed sensor.- signal, probable causes poor connection

P1723 Relay switch (this is a fail safe

P0715 Turbine shaft speed.

Relay or sensor, This depends on how the code appeared. When a ECM detects a problem it looks for opens short,ground and rationality,,Then there are codes that appear logic,because your taking of with low power you are in fail safe mode,to prevent you from reving and burning the transmission, so the relay which is powered by B+, go to the engine fuse juction box hopefully the fuse as labeled,look for a open fuse this includes the omega fuses (big ones) concentrate on the relay area to resolve this issue,723 and 715 are rational codes,Relay has no power If you can t find it let me know I will post a diagram

Comments

Thank you very much.

The weather has been relatively warm the past few days and it appears that it will continue for a few more days (above 25 degrees).  

The Elantra currently runs absolutely perfectly (for over 50 miles).  

Two days ago, I did check the Transmission fluid; I filled it with about 3/4 quarts of A/T fluid.  I do not if this is relevant or not.  

I will check the fuses shortly.

Thank you again