A 1997 Hyundai Tiburon came to a shop in Chicago with codes P0743 (TCC Solenoid circuit fault) and P0747 (Pressure Control Solenoid “A” circuit fault) stored in memory. This vehicle uses an A4BF1 transmission and was not in limp mode. The “MIL” was illuminated with no apparent driveability complaints.
As a time saving procedure (so he thought), the tech unplugged the solenoid connector and attached a complete internal harness and solenoid assembly “externally” using the battery as a ground (These solenoids are power side controlled and are grounded to the transmission).
He erased the codes and started the vehicle. Neither one of the codes returned. He then reattached the vehicle harness to the transmission connector and started the car. Both codes returned immediately. This was done several times and each time had the same results. Feeling confident that there was not an external problem in the wiring, he installed the internal harness and solenoids that was being used in the test. But once the vehicle was started, he had the same codes come up immediately.
Checks were then made with all the wiring from the transmission to the computer and all was well. The battery system was finally checked but all seemed well there as well. Since he had used the battery ground directly with the external solenoids successfully with his testing procedure, he decided to run a ground wire from the negative post of the battery to the transmission. Although the voltage drop test done on the negative battery cable checked perfectly fine, there was an apparent path to ground issue with the transmission. Since this ground cable fixed the problem, no further investigations were made to locate the compromise in the ground path. This was an odd problem indeed. Although checking the battery system wasn’t part of the initial diagnosis, even if it were, this would not have been so quickly discovered. Yet it is another testimony in the importance of power and grounds.
Subscribe to Motor Age and receive articles like this every month…absolutely free. Click here
