QuestionQUESTION: I have a engine light that keeps coming on and the code P0722 and they repaired computer with reflash and updates and put a stabilant to connections. It worked fine for about a week and than engine light back on again. Took it in and they replaced the pulse generator and cleared codes. Now again it worked pretty good for awhile but that damn engine light keeps coming on and they are not finding any codes so their logical opinion was that the transmission needed replacing. I took it to a transmission place to get a second opinion and they ran every test and said it was not the transmission but bring it back if the engine light comes on again. So about a week and a half later the engine light was back on and we took a test drive and the car does a move like trying to shift at 60 miles an hour and the transmission guy says it is a speed sensor that needs replaced. He had the scanner on during the test drive but when the engine light came it did not code anything. Why would not the engine code anything? His response was that if it doesn't happen more than 1 sec. the computer/sensor won't code anything. So now the Hyundai dealership was surprised that it was the speed sensor and not transmission and have offered to check my car again for free. I don't think they will find a code and how do I get them to figure out what is wrong with my car? Any suggestions on what else it might be? The only code they have ever got was P0722.
ANSWER: Hi, Karen. If the check engine lamp is coming on, there should be one or more codes in either the engine control module (ECM) or the transmission control module (TCM). I.e., if the problem occurs long enough for the check engine lamp to come on, it has occurred long enough for a code to store.
It does seem that the dealership is keeping an open mind and is attempting to help you. If the mechanic looking at your car is inexperienced, he may not realize that on this particular vehicle, no trouble code is stored in the ECM when the check engine lamp is turned on due to a problem causing a code to store in the TCM. On most other vehicles, there is a code that is also stored in the ECM to alert the technician that the TCM has requested the check engine lamp and that there will be additional diagnostic information in the TCM.
There is a technical service bulletin (TSB 03-40-022) addressing specifically the code P0722. So far, the people working on your car have done each logical next step in attempting to repair the issue. If we presume that you again have trouble code P0722 and continue to follow the advice of this TSB, the next step is to replace the transmission control module, and if still not repaired, the step after that is to replace the control harness.
It also may be worth investigating whether the vehicle speed sensor is working properly. The reprogramming you've referenced is intended to address a concern where externally induced electrical currents in the vehicle speed sensor signal confuses the TCM, causing it to think the output speed sensor (pulse generator B) is providing an erroneous signal. Similarly, problems with the vehicle speed sensor or its wiring could cause the same issue. Consider this a potential cause especially if your speedometer seems to not be accurate.
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QUESTION: I have taken it back to the dealership and they finally found these codes P0732,734 and 733 and they say the 2nd, 3rd, 4th rear ratios are fault and still say the transmission needs replacing. I have talked with the transmission people and they will check it again but they still don't think it is the transmission because it was the speed sensor that coded that day. Also could I have a problem with the throttle sensor? could it have gone bad? My speedometer has always been off by 2 or 3 mph since I bought the car in 2002. Would it make a difference?
AnswerYour throttle position sensor cannot cause these codes. Basically, these diagnostic trouble codes indicate that the TCM thinks the transmission is slipping in second (P0732), third (P0733), and fourth (P0734) gears. The TCM determines this by comparing the signals from pulse generator A (input speed sensor) and pulse generator B (output speed sensor) to the known gear ratios for the transmission in your vehicle. I've seen these codes occur in some cases without a pulse generator code when in fact the it was the pulse generator that was defective, but considering you've received the latest ECM programming and have had your pulse generators replaced, this is a highly unlikely scenario. Most likely, the dealership's diagnosis is correct; you'll need to replace (or overhaul) the transmission. If you're considering this repair, I'd recommend strongly considering doing it at the dealer. I've seen some real horror stories from transmission overhauls at chain shops.
The speedometer being off by two or three MPH won't affect what you're experiencing nor what I was originally referencing. That's part of the acceptable error of the speedometer itself. I was more attempting to determine if the vehicle speed sensor were somehow defective, causing P0722 to set again. Since that code has not returned, the speedometer question is pretty much moot.
