4L60E intermittent harsh shifts

[87Skier]

I've been having some issues with my 4L60E in my 96 Suburban.

After it is warmed up, shutting it off for a short time (10 minutes to 1 hour), then restarting all shifts (P to D or R, 1-2, 2-3, 3-4) are very harsh. 2-3 and 3-4 are less noticeable.

If I wait longer than 1 hour or restart within a few minutes the transmission shifts into gear and between gears smoothly.

I cannot replicate the issue while driving alone. It only happens when it has been started hot after sitting.

The ECM isn't reporting any codes and the check engine light is not on. The speedometer works without issue. I checked and changed out the throttle position sensor because it had more play in it that I liked. I verified it's functionality with a OBD2 reader. I am unable to view the transmission temp through the scanner.

The transmission itself was used when I got, and I've put 60,000 miles on it since being installed in 2015.

I had a harsh shifting issue in 2017 that was due to the brake light switch being defective. The brake lights are still working.

Any ideas what to look at next?

Thanks for any help

[AussieinNC]

Check the following in order...

Throttle position sensor
Vehicle speed sensor
Pressure switch assembly
Trans fluid temperature sensor
Engine coolant temperature sensor

Make up an additional ground strap and run it from trans to chassis
Make sure the trans mount is not broken

[Bigdav160]

1996 had a bulletin (or was it a recall?) for a missing ground plain in the ECM that usually resulted in low pressure and eventual clutch failure. Still, you should check the ECM service number to see if the correction had been made.

Your symptoms say the pressure is too high. That could certainly be the result of a trouble code (even pending).

I think I would install a pressure gauge just to verify correct pressures.

[87Skier]

Originally Posted by AussieinNC

Check the following in order...

Throttle position sensor
Vehicle speed sensor
Pressure switch assembly
Trans fluid temperature sensor
Engine coolant temperature sensor

Make up an additional ground strap and run it from trans to chassis
Make sure the trans mount is not broken

Thanks for the reply.

I drove it again this morning to see if anything had changed, and it started shifting harshly from a cold start. I don't think this changes much in what to look at.

So far:
TPS - good, verified through OBD2
VSS - good, verified through OBD2
Pressure switch assembly - will check
Trans temp sensor - any suggestion of how to do this?
ECT - good, verified through OBD2

I'll add an additional ground strap and check for the broken trans mount later today.

Originally Posted by Bigdav160

1996 had a bulletin (or was it a recall?) for a missing ground plain in the ECM that usually resulted in low pressure and eventual clutch failure. Still, you should check the ECM service number to see if the correction had been made.

Your symptoms say the pressure is too high. That could certainly be the result of a trouble code (even pending).

I think I would install a pressure gauge just to verify correct pressures.

You are correct on the ground issue recall. Mine has been done.

I agree with the pressure being too high, but there are no trouble codes stored or pending.

I don't own a transmission pressure gauge, but will probably buy one.

[87Skier]

The transmission mount looks good. I added a ground strap. I replaced the neutral safety switch because I've had a few issues with it not showing up on the dash. Still shifting harshly in the conditions described in the first post.


I'm going to pull the pan to replace the pressure manifold switch with temperature sensor and check all resistances of components inside transmission. Fluid and filter will get changed as well.

[87Skier]

Fixed.

I pulled the transmission pan, checked the resistance of everything in the pan and found no issues. Temp sensor resistance matched the current temperature.

I replaced the pressure manifold switch and everything seems good. Shifts were softer for a few drives and now it is shifting better than it has in a few years.

[Bigdav160]

Interesting results