Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
2012 Kia Optima will not move in low gear all other gears are fine stored P0731
2012 Kia Optima. No first gear. All other gears work fine Vehicle will not move in first gear but can be manually shifted through all other gears using manual mode.
Stored code P0731 for incorrect gear ratio. Consistent with the symptoms. If forced to move in 1st gear engine will race up and jump into limp mode. No other codes
The following is the operating table for this transmission based on this it appears that in low gear Shift Solenoid A and the 3,5,Reverse solenoid should be energized. Shift solenoid A is a steady on or off 3,5/R is a pulsed pressure control solenoid. All other solenoids should not be energized.
SS-A is on
35R is drawing 650mA - 800mA which is in spec
However, The 2,6 brake is showing a current draw of 250mA. My understanding is this solenoid should be off.
My suspicion is the 2,6 brake is staying applied partially in low gear and locking the transmission out.
In 2nd gear and 6th gear the 2,6 brake seems to operate normally and goes to 650mA -800mA draw. In all other gears when driving it drops to 0mA as if the driver is being properly turned off.
Note: These current draws are all off of scan data. I did not have my scope and need to go back with my scope. I am just trying to plan a course of action.
The questions that have me a little confused are:
Can a faulty driver partially leak some current and turn the solenoid on? If so why would this fix itself in all gears other than 1st? That doesnt make sense to me.
I also considered that there may be a partial short to another control wire. 1st gear and reverse are the only scenarios where SS-A is on and the 2,6 solenoid is not.
However, if that was the case where current was being drawn through another driver why would I see current displayed on the scan tool for a turned off circuit?
I did do resistance checks at the PCM between the power and control wires and resistances were within sec. high by approximately 1 ohm but I would think that is normal checking them from the PCM
Sorry for the long post. I think I need to go to the connector at the transmission first. I just thought someone may have experienced something similar and may be able to help with some direction.
I don't know if you've come to a resolution with this one yet. There's not a lot of transmission talk around here, it's certainly a skill set unto it's own, but based on the symptoms you describe if that car showed up in my bay in would get transmission rebuild or replacement.
We pulled the pan. There was no indication of transmission failure ie no metal and very little clutch material in the pan.
Since this is a high school auto shop class rather than a active repair shop we decided to test each shift solenoid using my fuel injector pulse tool. We found that Shift Solenoid A which controls the application of low gear was mechically sticking. Very little movement compared to shift solenoid B which is the same part number. After cleaning and solenoid A we were able to get more movement from it but to be safe we are replacing solenoid A and B. Alll other solenoids worked properly so they were cleaned and reinstalled.
We are waiting on parts and wll see if this and fresh fluid fixes the problem. If it does not we wil recommend transmission replacement.
That's pretty smart. Ive had mixed results using my injector timer on other solenoids. Let us know how it comes out in the end.
EDIT: I guess in hindsight, you could have done the same test from the PCM connector with an amp clamp around the circuits to see if there is any variation in the pattern that would indicate restricted movement, like the absence or placement of a pintle bump.
The end result was you were correct. It does need a transmission replacement or rebuild.
The solenoids did not fix the issue. The symptoms did however change slightly confirming that the first gear/reverse clutches are likely worn. It now moves forward one time in low gear when its cold. Then it will chatter and slip then it will not move at all in low. As the clutches get hotter.
I actually did sort of try what you suggested with the scope. I did not include that in my original post. I put an amp clamp on each solenoid control wire and commanded them on with the scan tool. I really did not see anything conclusive in that shift solenoid A and B wave forms were both identical.
I also checked the other pressure modulating solenoids which threw me for a loop. When activating one through bi-directional controls I was getting activity on others. I initially thought this was pointing to a wiring issue. However it was too predictable. We did a little research and found that this is normal activity. When energizing one solenoid its normal for the PCM to pulse others.
End of the day we overcomplicated what was simply a bad transmission but I think my high school students learned a few things so that part was successful.
Topic Author
