Transmission lock-up and Power Light

[JIMSVX]

Steve - I am now about 90% confident that I'm performing the TCU self-test correctly.

Originally Posted by SVX-FF

The tranny light will blink once every quater second if it is ok at the end of the test. If the "POWER" light stay lite, steady, then there is a problem. If the light does not blink at the end of the test then the test was not done correctly.
When you start the car or turn the ignition to the "ON" position the "POWER" light will steady lite for a few seconds and then go out.
Hope this helps, if not let me know and I will shot a video for you this weekend of the process.

Steve

However, when I turn on the ignition the only light that turns on and then goes out, is the Air Bag light. The Power Light stays on, along with all the other lights, as long as the ignition is on and the engine isn't running. I looked at the 4EAT on my '93 Impreza and the Power Light reacts the same way (without the engine running.) Out on the road the Power Mode and TC lock-up work as advertised.

I was reading the End-Wrench article "4EAT Phase 1 Transmission Diagnosis & Service" looking for a reason that my tranny is not working as advertised: http://endwrench.com/images/pdfs/4EATPh1Win04.pdf

On Page 2 & 3 it discusses the sensor inputs for the TCU. For the Temperature sensor it says:
"When the ATF is hot (AWD only), the TCU shifts the transmission as if in the POWER mode. This pushes the shift points higher which allows the engine to run faster. The oil pump then circulates ATF through the oil cooler more quickly so as not to overheat the engine coolant."

After reading this I wonder, what if my temperature sensor is defective and it provides the TCU with an incorrect/hot temperature input. If this is happening, is the TCU also keeping the TC from locking up, in order to keep the ATF flowing? Would this also inhibit the Power Mode switching when I try to kick it in with the throttle, since the TCU had already set up the tranny in Power mode? If this is the case, would the TCU self-test ignore this as a problem since it would see a temperature sensor that was working, regardless that it was getting a hot reading from the sensor? Also, what would happen to the Power Light when running the self-test with a hot temperature sensor reading? Would the Power Light stay on all the time (like mine does) and not blink like it should during a normal self-test?

What do you think? How can I test the temperature sensor? Looking at the wiring diagram it looks like I can make a resistance measurement at the TCU connector to determine this. The only problems are knowing what the correct reading is suppose to be at ambient temperature, and getting to the TCU connector up under the dash to make the measurement.

A little background on this car, a new TCU was installed in '01 at 86,000 miles and the tranny was rebuilt 18 months later at 103,000 miles by Camino Transmissions in San Diego. The clock is now at 125,000 miles. The previous owner said that he has never seen the TC lock-up. Camino told me to stop by and they would look at it (unfortunately they are located 2,000 miles away from here)!

- Jim