mountainmanjoe

I've got a 2013 Savana 1500 AWD with only 87,000 km (54,000 mi).
Vortec 5.3L with 4L60e

The transmission slips a lot. Low speed, high speed ... doesn't matter. At low speed, I can feel a lack of engagement between pedal and road. Up and down shift times are sometimes very lazy. When I get on the highway and put my foot into the accelerator, it's really noticeable. The engine revs to 6,000 rpm and there's little power to the wheels. I have to accelerate gingerly and it will eventually upshift.
There are no trouble codes. Fluid level is correct. It's clean, bright red, and doesn't smell burnt.

It started happening all of a sudden on a freezing cold day. I was late, and driving a bit briskly. It worked perfectly the day before.

Transmission control module failed last year, and was replaced.
Fluid and filter were replaced 4,000 km (2,500 mi) ago.

What can cause this?

William Kisselstein

Sounds like the module may have failed again. Have to get a good scantool on there and see if it can tell you what the transmission is doing.

mountainmanjoe

When it failed, the instrument panel lit up like a christmas tree. This time there's nothing.

My Tech2 shows no trouble codes. Is there anything in particular you would look for?
Fluid temp is perfect.
Input & output speed sensors appear to be working correctly.
TCC solenoid engagement seems to be working.
Obviously, shift times are delayed, and there's plenty of slip.

Triaged

Tech2 will show line pressure and torque converter slip percentage right? Likely PWM for TCC? I wonder if the torque converter isn't locking up? I know a bit about th350 but next to nothing about 4l60e other than newer transmissions rely heavily on the lockup torque converter to get a good combination of performance and economy.

tech2

does it happen in all forward gears, any change in manual 1/2?.
if the fluidv was burned and smelly nowor at last change its a sign. view the slip rate with your tech 2. if its excessive, the clutch pack frictions are probably worn.

hanky

Might be a good move to verify pressures are where they should be. Low apply clutch pressure starts the cycle of slip. overheat,wear and then loss.

mountainmanjoe

I will monitor line pressure and see what it does.
What do normal pressures look like?


Slip is around 700 rpm during shifts. It seems to be getting worse. How much is excessive?
I would be more inclined to believe clutches are worn if it happened gradually. But one day tranny worked perfectly, the next it did not.
And with such low mileage?

mountainmanjoe

This 4L60e does not have a pressure sensor. Tech2 only shows Pressure Control (PC) solenoid duty cycle and current.
TCC slip is provided in RPM (calculated from difference between engine speed and trans input speed)
TCC lockup has nothing to do with my issue. It won't even shift.

Manual gear selection makes no difference. At first it was slipping going into 3rd. A few days ago I lost 2nd as well. It's stuck in 1st now. No shifting happening at all. Not even slip.
P,R,N work fine.
Fluid condition has always been good.

mountainmanjoe

I checked fuses: TRANS, TCM BATT, TCM IGN. ALL were fine.
I crawled underneath for visual inspection. No leaks or loose connectors.

I spent some more time with diagnostics and data logging.
It seems all the electronics are doing what they should.
Shift solenoids are going through their motions. (I can even hear them clicking through the pan when I control them bidirectionally)
PC solenoid is responding to commands.
Speed sensors, ATF temp, throttle position, range switches, etc.. all good
I'm starting to think this a hydraulic issue. Valve body problem, fluid starvation, failed pump, etc.
Either way, I think I've done all that I could. I'm too busy to drop the pan or get pressure gauge fittings and diagnostics right now. I'm calling my tranny guy tomorrow.





This is some live data and plots I recorded:
https://www.youtube.com/playlist?lis...mY2Wu3rC5vKOrR

Triaged

Deep pan with standard filter?