We are experiencing issues with our 2010 shifting hard. No codes are being set.


When this occurs, stalling and restarting after five seconds usually fixes it, but in cool weather only when the car is relatively warmed up.




When connected to a scanner, I noticed that when cold the input speed sensor reading after start up in Park does not provide a reading, yet the TCM will not set a code.





If the engine is revved up high enough, you can get the ISS to report and the idle can drop and it will continue to report. Put the car in gear with brakes applied, it goes back to 0 rpm (normal) then putting it back into park/neutral, the value stays at 0 rpm (does not seem normal).





Usually when ISS behaves in this fashion and the car is driven, eventually as speed/rev is increased the ISS value suddenly appears (several hundred or over 1000 rpm, and varies normally). When this happens, the pressure control solenoid value Duty Cycle / Amperage suddenly freezes and no longer changes with load. Whatever value it freezes will usually project how harsh a shift will occur as it no longer modulates the signal and transmission shifts rough (the degree based on what the value froze at).




Turn the car off for 5 seconds if suitably warm, restart. Instantly the ISS signal shows proper input speed, pressure control solenoid varies with load. Car will drive suitably for remainder of trip, perhaps even next few drives that day. Likely on the following day, cool morning ISS will not be displayed and suddenly appear while accelerating, then same nonsense with hard shifting/frozen pressure duty cycle/no control.





Thinking internal TCM damage (as the ISS signal at least did not seem any different with a multimeter connected while malfunctioning) we swapped in a trial TCM. Same issue surfaced. I recently tried a PCM and same issue surfaced.





I am wondering if the ISS signal is actually somehow bad however the computer does not set a code for it?


I have cleaned the MAF connector, as we did run into an issue at some point with constant locking/unlocking of torque converter which after clearing the MAF connector pins with small pliers and using electronic cleaner in the connector, worked - never occurred again.





I thought perhaps some TCM calibration adjustment could be at play, just wondering if anyone has experienced such an issue? I am ready to get an ISS but have to take the side of the tranny cover off I believe to get to it. I checked grounds on the front of the transmission, they are OK however some small voltage drops between it it and the engine are present. The PCM has a similar drop, close to 200mV. I jumped a ground direct to the TCM and tried to the PCM to see if there would be a change and it still occurs.




All that said, drive the car in sub 32F weather, smooth shifting for some time - on windy cold conditions such as flurries and randomly the car will suddenly buck as if the transmission control is being affected. Colder weather, no wind - works great. Usually summer in hot weather no shifting issues noticed... just perhaps on cooler mornings, sub 60F weather.




Any of this make any sense? Should I perhaps take the ABS module out of the equation by removing the fuse to see how the system fares with the output speed sensor input vs having ABS input speed in the mix?




I never could set a transmission code, unless I stalled the engine while moving and restart it while moving... can get it to set an ISS related code by doing so (likely unexpected). The only other code that can eventually surface in operation now is an EVAP performance code however I can not see how this would cause the ISS input value to not appear after startup.





Desperately trying to isolate this. Please help!




Sewie

 

What is the coolant temp when this happens?
When you say no codes set; no pending, current or historic?
Have you looked at the output speed sensor connector?
Have you looked at the input speed sensor connector?

Your description might be water or ice shorting a connector; they are both under the trans.

There are codes for ISS performance and OSS intermittent or low voltage.

I suspect a pending or intermittent engine code.

 

I had a problem where the ambient temp would effect my shifting.

https://www.chevyhhr.net/forums/driv...en-cold-56252/

 

It had nothing to do with the ambient temperature.

 

Thanks for your interest donbrew.




The coolant temp is usually sub 180F, perhaps 170F when even after restarting the harsh shifting reoccurs with the lock up of the solenoid duty cycle pressure. Reason I say this is if the car is restarted as soon as the harsh shift occurs, usually it will happen again until restarted after sufficient temp is built up. There have been exceptions to this rule (shifts normal right away - perhaps duty cycle of solenoid freezes at different level), however mostly behaves as per above.





Regarding codes, correct no pending, current or permanent codes are currently set. That goes without saying we did have a secondary O2 go out which was replaced and fixed that code, as well EVAP pressure sensor was a bit out of range (2v at atmospheric vs 1.4v or so). That was replaced and we are not seeing the EVAP performance code.




Both those codes should not have been driving the TCM in such a mode to have issues reading the ISS signal.




So, right now I got in the car. Engine coolant temp is 12C. Intake air 23C. Trans temp 13C. Oil temp 27C (not sure how it can be that high, perhaps I should suspect something here?) trans temp 14C. The 27C this is actual engine oil temp?. The ISS value as soon as I started it was read. No issues. I suspect the car would operate normally.





The car can be very dry, just cool weather would trigger the symptom. I can not see freezing being it, *maybe* some moisture though seems abnormal.




I too would have thought an ISS code would be generated and the only way I can get one to be created is by stalling the car while moving in neutral, and restarting it. It seems if the car is moving and the vehicle is forced to start coasting it is easy to generate an ISS code (reports no signal). Otherwise, if the car is restarted with a parked vehicle, no code is generated.





It is a very strange issue and sometimes I would like to be able to follow the programmer's logic behind it all. Other than the oil temp being higher than I would think it should be right now, I would say the lack of ISS on startup when cold is a red flag so I am wondering if others have seen this. It should not take me revving the engine in park or neutral to generate a signal, and then only have it drop to 0 in drive and when put back into neutral not come back up until I rev the engine. Again, if warm, no issue!!







Cheers,

Sewie

 

It is interesting you mention this and I see the other reply that it does not affect it. I would think the same way.

I heard something about someone saying the ambient sensor reading sensor had to be cleaned.

One way I would think to isolate may be to completely fault the reading as in remove the sensor and try driving?

Perhaps I need to monitor the oil temp (seems higher than I would expect for a sitting vehicle) and the ambient for "intermittent" reports, like spikes in the reported value that perhaps the cluster is filtering in its display.


Sewie

 

170F is TOO cool. Anything under 180F will trigger P0128 as a pending code (no CEL).

 

I do not see P0128. The car eventually warms up as per norm. What I am saying is, from a cold start in a "cool" environment (sub 55F), very often the transmission input speed sensor value on a live scan will be 0 rpm when in neutral, when running. This should not be I would think right after start up.

As of right now I have completely disconnected the ambient sensor so as to not provide any input. I actually removed the two ABS fuses as well to see if the transmission output speed, or even speedometer reading will be affected. I want to leave out any ABS chatter during these tests.

Obviously I will have to wait for a cool start up again with cold ambient temps to see what happens. When it happens again, I think the likely culprit may just be with the ISS of the trans itself, despite what the computer stores for codes. That is just my thought.


Sewie

 

[QUOTE][The coolant temp is usually sub 180F, perhaps 170F when even after restarting/QUOTE]

The temp should always be above 180F after it warms up in about 5 minutes or less. If it takes more than about 5 minutes to warm up that is also bad. I don't care if you are reading codes or not. Your t-stat is stuck open, if that quote is true.

This is a case of too much information. You are getting way too much professional information and interpreting it as an amateur.

10 years of experience on this forum leads me to this conclusion. Get a new ACDelco 131-158 T-stat installed and give me $.02 if your hard shifting goes away.

 

Good day donbrew,

What I am stating is this is the maximum temperature at which the ISS usually will not register any reading after start up. This problem exhibits itself as soon as the vehicle is started (cool) and will reoccur if I simply stall for 5 seconds or so and restart, unless the engine has been warmed sufficiently (within a few minutes). After sufficient warm up,a restart usually clears the ISS problem and it will report as soon as the vehicle starts and in turn transmission shifts properly.

It almost seems like either ambient air, intake or coolant temp trigger a null ISS reading when the engine is started however that does not really seem logical. What sounds more logical is that perhaps the ISS is failing to produce a quality signal until sufficient warm up, perhaps of the trans itself. I have metered the ISS and saw that it would vary as it should though perhaps the signal is degraded slightly during the time where the TCM reads 0 rpm on that input.

I thought I would mention, when "cold" the ISS value is zero when in park so I put the car in gear and drive forward I would expect to see readings, but I do not. Without an ISS signal, the pressure solenoid duty cycle is varying with the load on the engine (as it should). Suddenly, if the ISS value appears, it is at that point the TCM suddenly freezes all pressure solenoid control, and the transmission shifts harsh based on DC value it froze at. It is when I restart the car that the control over the pressure solenoid is suddenly restored. If again not warm enough and ISS is not reporting, the same will reoccur.

I did consider thermostat however it holds the temp over 179F without issue even in really cold weather.


Sewie