Hyundai Repair: Hyundai Accent GS 2001, transmission control module, hyundai accent

Question
2001 Hyundai Accent GS, 106,236 miles.  The check engine light came on and then went away, then it came back on later that same day and stayed on.  I went to Auto Zone and the guy check it there and said something about transmission codes, he reset it and told me to drive around and if it came back on to come back.  He said not to go to dealer cause they would make it a bigger thing and charge me more.  I went to get a print out of the codes and I got these codes P0734 Gear 4 Incorrect Ratio, and P0722 Output Speed Sensor Circuit No signal, I went to get inspection and the car passed ;), drives okay, nothing really major, but seems to be little rough.  How do I fix this and what am I looking at in repairs prices, I am strapped for cash, I am a student, and this car has been great to me so far.

Graciela  

Answer
Hi, Graciela.  P0722 means that there's an output speed sensor fault and P0734 means the transmission is slipping in 4th gear.  But the TCM (transmission control module) cannot effectively determine whether the transmission is slipping if the output speed sensor signal is not correct.

Hyundai actually has a TSB (technical service bulletin) about this issue, 03-40-016.  Effectively, the TSB says the problem is that the TCM incorrectly reads electromagnetically induced noise as well as the output speed sensor signal and gets confused.  It says to reprogram the TCM and check the output speed sensor.  

Unfortunately, the dealer will be the only place that can do this repair, since it involves a reprogram.  If you call them and ask how much they'll charge for the work outlined in the TSB, I'm sure they'll tell you.  

Realistically speaking, this problem will show up only intermittently.  When it does, the TCM will put your transmission in failsafe (third gear only).  Turning your car off and back on should return your transmission to normal operation.  If it does go into failsafe, do not continue driving in third gear only.  Starting from a stop in third gear causes significant strain in third gear and will eventually cause damage to the transmission.