QuestionQUESTION: I have a 2002 Hyundai Sonata V6. I took it to a dealer and the only code is a clu/tcu communication line #1, dtc p1602. They tell me that I need a replacement Trans Control Module. Could I still drive the vehicle with the manual shifter safely and not damage anything further? Thanks.
ANSWER: This code simply indicates a problem in the communication line between the engine control module (ECM) and transmission control module (TCM). If your transmission is in failsafe (third gear only) due to the fault-- and if my memory is correct, it will go into failsafe when the problem occurs-- you won't be able to shift manually using the shifter, either.
Although the TCM is one potential cause, the most likely cause is a problem with one of the two wires between the ECM and the TCM being rubbed through the insulation on a metal component. When this occurs, the communications network is effectively shorted to the negative battery terminal and cannot work properly. Other potential issues cold be with the ECM or, if equipped, with the ABS module.
It's unlikely that any repair for this issue will be inexpensive. None of the modules are cheap, and you're often looking at a significant amount of labor time to simply locate a problem in the wiring. If you question the diagnosis, I'd recommend taking the vehicle to a shop with a stellar reputation in electrical/electronic repairs. You'll need someone who will be candid with you regarding what is and is not occurring when they look at the car. If the problem isn't occurring at the time the vehicle is inspected, there will be no meaningful test results, and I'd recommend not attempting repair until it can be determined whether the problem lay in one of the modules or the wiring.
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QUESTION: Thank you for responding so quickly. I do have a few more questions. Today I visited the dealer again, and asked him why when I drove my car to him the other day, (a few days after the inital problem) I did not experience the hard shifting. He responded there was a fluid, when heated enough would cause a recurrence of my problem. Also in responce to my car being in limp-mode I have not experienced it. I drove it home when the hard shifting occured. And drove it only one more time, to the dealer, and there was no problem (about 8 miles). Could water inside the vehicle cabin create a short somewhere down the line. Maybe liquid spilled on the dash or radio? Thanks again !
AnswerThe wiring (and control modules) are high enough in the interior of the car that the only way they'd be affected is if the car had been in flood water. Additionally, it'd be highly unlikely that anything could be spilled into these areas.
The hard shift you experienced was likely the transmission shifting into 3rd gear for failsafe. The reason it hasn't happened since then is that the problem hasn't actually occurred since then. P1602 is a purely electrical problem and has nothing to do with fluid. Additionally, if the problem is very intermittent, this further supports the idea that it's in the wiring and not the module. Consider a wire just barely rubbed through the insulation. Change in temperature or the movement of the vehicle can be enough to make it touch or not-- remember that the reason these type of problems occur in the first place is due to wiring rubbing over time. If I'm correct, the problem will get more frequent over time until it's to the point where the vehicle can be tested with the problem occurring. Unfortunately, if there's a poor solder joint in a module or a crack in the circuit board, the same type of intermittent symptoms can occur.
I've had exactly one vehicle with this problem, and it was intermittent. This problem occurred in the summer, and I found that after the vehicle was inside and cooled, the problem went away. As I recall, it took several trips in/out of the service bay over two or three days to determine for certain that the problem was in the wiring. In this case, the two communication wires were shorted to each other.
My guess is that in this case you spoke to a service adviser who doesn't care about facts but rather about whatever will get you to go away happily the soonest.
