Hyundai Repair: 2000 Hyundai Sonata - Transmission, amp fuse, hyundai sonata

Question
A week ago, my daughters Sonata lost power (pickup) and the check engine light went on.  The mechanic ran diagnostics which gave a code like p1723.  He said it was the Transmission relay.  After he replaced the part and cleared the codes, the symptoms still appeared (transmission in failsafe mode, transmission would jump or slam in reverse etc)  He went to the fuse panel and found the 20 amp fuse was blown.  He replaced the fuse.  Transmission was now operating normally.  No Check engine light etc.  He took it for test drive and all was well until the car shifted from 1st to 2nd.  At that point the car lost power, check engine light went back on and were are back to failsafe mode.  
Any suggestions?  Could this be a bad speed sensor?  Please advise as this guy keeps saying the Hyundai is a cheap vehicle and the transmission should probably be replaced.  

Answer
P1723 is indeed the code for the automatic transmission relay.  Hyundai has actually issued a technical service bulletin (03-40-014) for diagnosing and repairing vehicles with this code.

The blown fuse is the reason for the code.  Chances are that the fuse has again blown.  What'll need to occur now is to find out why the fuse has blown.  There could be a short circuit anywhere in the wiring between the fuse, the relay, the TCM, and the transmission, including inside the transmission; or a shorted transmission solenoid.  

My first recommendation would be to take the car to the dealer.  The dealer will have the factory scan tool, which will be capable of activating the transmission solenoids one at a time.  The techncian there can use this capability to help him learn which specific circuit the short is on, if the short is occurring when he's doing the test.

At the very least, you should get the car away from the guy that says you need a transmission.  If the problem is inside the transmission, replacing it will solve the problem, but there is no question this is an electrical issue and does not require the replacement of the transmission.  Even if the problem is inside the transmission, repair will require replacing a harness or soleniod inside the transmission, which will be significantly less expensive than replacing the entire transmission.

I encourage you to look at the technical service bulletin so you understand the nature of your problem.  You can view it at www.hmaservice.com.  The site requires Internet Explorer, and you'll need to register for a free account.