Hard Shifting, No ISS on Start, No Codes
We are experiencing issues with our 2010 Cobalt 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! I see other posts with P1810 - never had such a code.