4L80 1-2 hard shifting now all of a sudden

[Reluctanse]

Ok not a GMT400 but-
Wife’s 2007 Suburban 2500 with 6.0/4L80 started shifting hard been 1-2 recently, during normal driving. Trans was rebuilt about 45k miles ago, been drama free since then until now. Everything else behaves normally.

I replaced the filter about a year ago. No SES light, no store codes.

I am running a fairly stock tune, pretty much just adjusted for bigger tires(275/70r17s). I reflashed the stock tune, reflashed the current tune, unplugged the battery for an hour, and it’s still behaving the same. I reset the transmission learning in HPTuners. No change.

I don’t even know what to look for or log, but I do have HP tuners.

Thoughts?

 

[NickTransmissions]

Ok not a GMT400 but-
Wife’s 2007 Suburban 2500 with 6.0/4L80 started shifting hard been 1-2 recently, during normal driving. Trans was rebuilt about 45k miles ago, been drama free since then until now. Everything else behaves normally.

I replaced the filter about a year ago. No SES light, no store codes.

I am running a fairly stock tune, pretty much just adjusted for bigger tires(275/70r17s). I reflashed the stock tune, reflashed the current tune, unplugged the battery for an hour, and it’s still behaving the same. I reset the transmission learning in HPTuners. No change.

I don’t even know what to look for or log, but I do have HP tuners.

Thoughts?

Check live data streams for the trans and torque converter as well as engine management sensors like the throttle position sensor. Also put a pressure gauge on it to see if you have high line pressure.

 

[Sean Buick 76]

I would take it back to the trans builders shop and ask them to check the line pressures while driving.

 

[NickTransmissions]

I would take it back to the trans builders shop and ask them to check the line pressures while driving.

If he has high line pressure, it will show up at idle- he can test this at home. Worn boost valve/sleeve is the most common cause (and wont set any DTCs), followed by a failed EPC. TPS, esp the sudden appearance of a harsh 1-2 shift can also be behind it but I'd think he would see the TP position's way out of whack via HP Tuners live data...Additionally, driving the vehicle too much longer with this condition risks blowing out the case lugs at the intermediate clutch.

@Reluctanse - You can order a transmission pressure gauge off Amazon for $30-$40; dont use an oil pressure gauge as the pressure generated by transmissions exceed what an engine oil pressure gauge was designed to handle.

If high line pressue is present, and you're not comfortable working on the transmission, you should have it towed to the trans shop where they can do a full diagnosis and let you know what's up.

 

[Reluctanse]

OK we might have some good news here.

Hooked up HP tuners and set up some more throttle positions PIDs... it was set up for my 2000 which is cable throttle. So I rescanned and added the correct throttle PIDs, and it is ALL OVER THE PLACE. Verified by light throttle in the driveway, the RPM's and throttle position surge pretty significantly.

Will get the TPS (or pedal? this truck is DBW) sorted and report back-