Shift Pointers
- Subject: Codes P0743 and P0747
- Unit: A4BF1
- Essential Reading: Rebuilder, Diagnostician, R & R
- Author: Pete Luban, ATSG Technical Supervisor
I got a call from a technician about a month ago concerning a problem with a 1997 Hyundai Tiburon with the A4BF1 transmission. The technician explained that the MIL (malfunction indicator lamp) was on and codes P0743 and P0747 were stored.
As shown in Figure 1, P0743 indicates an electrical circuit fault with the TCC solenoid, and P0747 indicates an electrical fault with pressure-control solenoid A.
The transmission was not in limp mode and there were no drivability complaints, which in itself signifies that there is a skunk in the woodpile.
A number of circuit checks on these two solenoids found no problem. Usually when this happens one would suspect the TCM, but hey, the car is not in limp and it drives fine. The one thing I hate more than calls on noises is telling someone they need a computer and then having them call me back and saying “It’s doing the same thing.”
The technician also did voltage-drop tests on the TCM ground circuits, which came up good as well. The battery, battery cables and alternator output were all normal. So where to now?
The technician working on this car is a knowledgeable one. He decided to plug a known good set of solenoids into the vehicle harness outside the transmission, grounding them directly to the negative battery cable. And guess what – the codes were cleared and they did NOT return.
Just as a test to confirm the fix, these known good solenoids were installed into the transmission, and the codes returned on startup.
The only explanation here is that a ground problem exists in this vehicle somewhere, but when a job has to go you have to use some logic. The technician figured that if grounding the solenoids when they were connected outside the transmission cured the problem, then grounding them when they were inside the transmission also should cure the problem.
So how would one go about this? In Figure 2, the technician is pointing out a new ground cable that begins at the negative battery cable. Figure 3 provides a closer view. The other end of the new ground cable was attached directly to the transmission case as shown in Figure 4.
This did take care of the problem permanently, but guess what – a month later, almost to the day, another 1997 Tiburon came in to this same shop with exactly the same complaints!
Did a new ground cable cure this Hyundai? You bet it did! Anything can happen in Trannyworld.
Many thanks to Dominick Pietrantonio from AC Transmission in Addison, Ill., for sharing his experience with me and for supplying the photos that made this article possible.
