QuestionMY 2001 Hyundai Sonata v6 was a gem for the first years and 40,000 miles or so when suddenly, last year, the car started running very strangely...the check engine light would come on, and when this happened, the car would run very strangely...I brought it into the dealer and they said that a speed sensor went and I was covered for one more week...yay...they fixed it...
6 months later, same symptoms...check engine light would go on and off periodically...when it was on, the car would behave very sluggishly (had to give it a lot of gas to get it moving...seemed to run with a high # of RPMs indicating possibly a delay in shifting gears?)...this was accompanied by periods of the RPMs just spiking (even when sitting still) over 4,000 and climbing...brought the car in and was told a number of codes all traced back to a couple sensors, which were fixed (sorry, I can't recall the specific codes but one related to the themostat/coolant)....those were fixed and the car ran well again for about 4 months...
Now, the car is acting up again, and acting very much the same way...I just had the computer diagnostic run and got these 3 codes, p1529, p0720, and p0712.
IS this the same problem that keeps recurring? Or is it possible that my 46,000 mile car has this many failures? I really would appreciate any tips you may have...thanks.
AnswerIt's difficult for me to reach a good conclusion because I don't know what was done in each instance, but it would appear that each problem is probably different. In the first instance, I don't know which speed sensor was replaced, but I'd suspect it was either the input or output speed sensor. In the second instance, it would appear that the coolant temperature sensor was at least part of the issue. And in your current problem, you have P0712 (transmission fluid temperature sensor signal problem) and p0720 (output speed sensor signal problem). P1529 is simply an indicator that the transmission control module (TCM) requested the engine control module (ECM) to turn on the check engine lamp. The short explanation is that as long as the required fix is different, the failures are separate.
In this case, you probably have a problem with the output speed sensor itself (P0720), but I've seen P0712 arise due to shorts or open circuits in the wiring as well as issues with the transmission fluid temperature sensor. To make matters worse, the fluid temperature sensor is inside the transmission pan, which is hard to remove. There will need to be further diagnosis done to determine whether the problem is with the fluid temperature sensor or the sensor wiring.
