Question-------------------------
Followup To
Question - Trouble code P0753 is Shift Solenoid A Electrical Malfunction, i.e. short or open circut. None of which applies since all continunity, resistance and voltage measurements are within specs.
Your statement:"The ECU compairs the speed from the sensor in the top of the trans. to the vehicle speed." What are the connection names? Is this the function of the "Pulse Conversion Circuit" from the Speed Sensor in the trans? (page AX2-11 of service amnual)
"If it sees a difference of something like +/- 5%." How is this difference measured?
Does one clean the valve body in a bath or simply blow it out?
Thanks again - Jack
Question: What signals the ECU to switch to the "fail safe mode?" I have asked another expert this question but have not received a logical answer.
Symptom - Will not downshift to 1st gear when stopped.
Trouble code P0753 - Replaced both solenoids- no immediate change but over the past few months the shifting has become hit-or-miss.
Installed monitors on solenoid #1 and #2 lines from ECU to Trans. This monitor displays the presence of voltage on the solenoid lines.
When the transmission if functioning correctly the shifting indicates Solenoid#1 on in 1st. Both on in 2nd, #2 on in third and both off in OD. During this time the check engine light is extinguished.
When the trans does not shift I shift the gears manually. The following indications are:
In drive or park, only solenoid #2 is active. In drive this occurs with or without the engine running.
When shifting from neutral to drive I see solenoid #1 flicker before solenoid #2 activates. The previous expert said the solenoid coub be cloged. I agree with that but it does not answer my question.
The ECU has received some signal indicating a failure and is programmed to revert to the fail safe mode. What could that signal be?
The solenoids are simply turned on or off from signals from the ECU. They cannot provide feedback to the ECU but can cause a condition to exist that will cause something else to send a signal to the ECU. Can you explain how the speed sensor circuitry comes into play here?
Your resume is impressive and I hope you can shed light on this problem. I cannot find a Toyota Technician that can diagnose past "replace the transmission." I really cannot justify spending 2-3 thousand dollars on a car worth $3000 max to fix an intermittent problem.
Thank you in advance for your expert opinion and advice.
Answer -
The ECU compairs the speed from the sensor in the top of the trans. to the vehicle speed. If it sees a difference of something like +/- 5%. It shifts the trans into "limp home" mode.
I suspect that you have a plugged solenoid in the valve body.
WINNS makes a trans flush machine that interuputs the flow to the radiator. That combined with dropping the pan and cleaning out the valve body manually would be about all you can do.
What is the p0753 code? solenoid malfunction?
Im not at work and cant access TIS from this computer.
Mike
AnswerAt the last Auto trans class I attended, a few years back, I remember the instuctor saying the ECU compairs the vehilce speed to speed sensor #2 and said a 3-5 % difference was allowed, I think it reads off the direct clutch. Basically he was saying that if something was slipping internally the ECU detects it and puts the trans into 2nd gear.
I think you just have some clutch material or metal plugging something up.
I dont really care how its calculated,just want to get the car fixed for you.
Drop the pan, clean the screen with brakleen. Clean the port that the solenoids are attatched to. Flush, flush , flush.
Replace solenoid A. There was a problem at some point or it would not have stored that code.
About 2 out of 10 vehicles with this code Ive worked on have required trans replacement as the debris could not be sucessfully removed.
There are check balls in the valve body so beware should you decide to take it apart.
Also- Toyota has a reman-exchange program thats why most Techs now say "put a trans in it"
Mike
I just remembered a while back I had a shifting problem I chased for a day or two that ended up being a nuetral safety switch that was worn out. Thought of it when you mentioned the one solenoid "flickered"
Mike
