Mechanics

TRANSMISSION CONTROL MODULE-CAN BE FAUL

1998 Hyundai Accent

Transmission problem
1998 Hyundai Accent 4 cyl Front Wheel Drive Automatic 128000 miles

Hi,
My daughter acquired a 1998 Hyundai Accent which apparently didn't have a functional OD but ran very well, at least for a little while. Trouble codes indicated a bad 3rd gear and some 02 sensor codes. A friend and I installed a used transmission, which after taking out the battery cleared the check engine light. During the test drive, I took it up and down the road several times, and it shifted quite well but I didn't think I was getting up enough speed because it didn't seem to be going into overdrive. I took it out onto a highway, where I decided to try the OD button. When I tried turning the OD button off (out), the car bucked for a second, I turned the OD button back on (pushed in) and I decided to pull off the road. I quickly realized that I had completely lost any drive and was just coasting to a stop. Strangely the MIL (check engine light) never came on, and still doesn't (although I haven't checked to see if there are actually codes or not). After getting the vehicle back to the house and some troubleshooting, we found that a previous owner had rerouted the OD button wiring incorrectly and the insulation had worn away. This button takes a +12V supply and sends it to the Tranmsission Control Module, or to the dash OD Off light. I had known that the button previously did not turn on an OD off light but hadn't checked it out since I knew the transmission was bad. The only thing I can think of that could have happened is that the wire to the transmission control computer became grounded when I let the switch out and this caused something bad. The only concern I have with that, is why now? I had fiddled with that button numerous times on the old transmission without frying the TCM. We have repaired the wiring, check the PCSV for functionality (resistance and 12V operation), replaced the shift range control switch on the transmission with one from the old transmission, and turned the tires while off the ground to see if the half axles had somehow become disengaged.
That being said, I am in the process of looking for another TCM but can you suggest any other troubleshooting? Is there a way to see if the TCM knows it is in drive? When I put the vehicle into R or D etc, the engine idle speed does increase like it is ready to engage. The PCSV should have a duty cycle of around 80-90% in Drive and idling. I haven't put on oscope on it yet, but a dvm only gave me a readout of around 1.9V in Drive. I am assuming that since it was suggested to try operating it externally at 12V, that this also should have related linearly to the high of the duty cycle, giving me around 8.5 -10.8V. I could be wrong about this.
If the torque converter had not been inserted fully, and it damaged the oil pump, wouldn't this have become quickly apparent (it did drive perfect for about 10 mins up until I tried the OD button)? Any suggestions?
Thanks
Jeff
Avatar
Fuz
March 1, 2009.



Hi Jeff,

Thank you for the donation.

When TCM faults are detected, it usually goes into fail safe mode whereby it would either be locked in 2nd or 3rd gear. You should be able to limp home unless you have damaged the trans to the extent the clutches are burnt or the planetary gears have been damaged badly.

If the fluid level is correct and you do not have any burnt smells or fluid turning brown or black, it should not be the trans problem. I would suspect the torque converter to be faulty.

If you have an analog voltmeter or LED test lamp, you can retireve the Diagnostic Trouble Code (DTC).

Otherwise you get get a free scan done. Most parts outlets provides this service.

KHLow2008
Mar 2, 2009.