6L90 won’t shift into 4th after rebuild

[Nate-B]

Reverse.....

Thank you! I was out this morning making sure that everything was all good with the valve body. Im going to put it back in with the old TECHM, because at least during my first test drive if definitely attempted to shift up into 4th, now I don’t even get a rev like it’s in neutral.

However, when checking the valve body again I noticed that pretty much everything in the upper valve body with a new Sonnax end plug, like the 1-2-3-4 clutch regulator valve, they spring back normally in the bore, but if I push in on the end plug, they get stuck. The rubber seal gets caught on opening one inside of the keeper. Could this be causing my problems? I assume if they get caught and stuck when they’re cold (around 35/40) they definitely would when they warm up with the fluid.

If this is a real issue. New valve body? Or should I just order a set of the regular GM end plugs that don’t have the rubber seal that the Sonnax one does?

 

[Nate-B]

Thank you! I was out this morning making sure that everything was all good with the valve body. Im going to put it back in with the old TECHM, because at least during my first test drive if definitely attempted to shift up into 4th, now I don’t even get a rev like it’s in neutral.

However, when checking the valve body again I noticed that pretty much everything in the upper valve body with a new Sonnax end plug, like the 1-2-3-4 clutch regulator valve, they spring back normally in the bore, but if I push in on the end plug, they get stuck. The rubber seal gets caught on opening one inside of the keeper. Could this be causing my problems? I assume if they get caught and stuck when they’re cold (around 35/40) they definitely would when they warm up with the fluid.

If this is a real issue. New valve body? Or should I just order a set of the regular GM end plugs that don’t have the rubber seal that the Sonnax one does?

Wait, never mind. I assume the end plugs should be snug in the bore, that’s the whole point of the sealing rings. Nothing would push from the keeper side like I was. Apologies.

I think I’m still going to throw the old TECHM back in when I get home and compare pressure readings to your video and see how that goes.

 

[Nate-B]

I got the old TECHM installed today and it didn’t go super well. It did get to above 80 degrees without losing reverse, so that’s different than the “new” one. However, it immediately threw a CEL and had the following codes:
- P0967 CPC Solenoid #2, Circuit Voltage High
- P0971 CPC Solenoid #3, Circuit Voltage High
- P2721 CPC Solenoid #4, Circuit Voltage High
- P2730 CPC Solenoid #5, Circuit Voltage High

They were immediately current and came back as soon as I cleared them. So unfortunately I wasn’t able to get any solenoid data, as it immediately locked itself in gear (I can’t remember off the top of my head if it was 3rd or 4th, but I would assume 3rd since it never even shifted). So is the one one bad? I’d like to try and get some shift data before assuming that I need yet another new TECHM.

@clinebarger at this point, do you think you could help if I sent you the VB and the two TECHMs that I have? Or would you need the whole transmission?

 

[clinebarger]

Ideally I would want the whole truck, Second best would be the whole unit....I would install it in my truck after a Clutch Air Test, Going through the Valve Body, And checking the TEHCM (Solenoids for physical operation & Progamming/Calibration)

Sending me just the Valve Body & TEHCM will at least eliminate them as an issue, I will go though the above tests AND install it in my 6L90 to PROVE it functions correctly on a known good unit.

Lucky for you....My L96/6L90 is also a 2013 model, Meaning both of our TEHCM's have the same Operating System & very likely the same Calibration.

 

[Nate-B]

Ideally I would want the whole truck, Second best would be the whole unit....I would install it in my truck after a Clutch Air Test, Going through the Valve Body, And checking the TEHCM (Solenoids for physical operation & Progamming/Calibration)

Sending me just the Valve Body & TEHCM will at least eliminate them as an issue, I will go though the above tests AND install it in my 6L90 to PROVE it functions correctly on a known good unit.

Lucky for you....My L96/6L90 is also a 2013 model, Meaning both of our TEHCM's have the same Operating System & very likely the same Calibration.

I’ll send you a message.

 

[panthermike]

I’ll send you a message.

Please update down the road, would love to hear how this turns out.

 

[Nate-B]

So I ended up ordering a whole new VB and TECHM right from GM, price wasn’t too bad. They came in today so I got the VB together and everything installed in the truck. I used GM Techline Connect again to program the new TECHM. Now, I can’t even get the truck to start. The IMS is showing the truck in park, and it’s displayed on the dash (it’s also physically in park) but for some reason it won’t even crank. If I go into ECM data I can find that it says “in gear” next to PNP.

Both ECM and TCM (and BCM) are up to date with current calibration in SPS2. This is a brand new TECHM, so I’m a little confused. The transmission knows it’s in park, but the truck doesn’t? Any ideas?

 

[clinebarger]

The P/N signal is hardwired directly from the IMS to the ECM, Separate from the PNDM indicator circuits in the IMS.

Shift the shifter to M, Then back to Park......If the display doesn't return back to Park....The IMS is not hooked into the Manual Valve or the Manual Valve isn't hooked onto the "Rooster Comb"/Manual Detent correctly.

 

[Nate-B]

The P/N signal is hardwired directly from the IMS to the ECM, Separate from the PNDM indicator circuits in the IMS.

Shift the shifter to M, Then back to Park......If the display doesn't return back to Park....The IMS is not hooked into the Manual Valve or the Manual Valve isn't hooked onto the "Rooster Comb"/Manual Detent correctly.

I can shift though everything and the display will change accordingly, always returning to Park. Even if I view transmission data with the scan tool, it shows accurate changes while I move the lever.

 

[Nate-B]

I can shift though everything and the display will change accordingly, always returning to Park. Even if I view transmission data with the scan tool, it shows accurate changes while I move the lever.

 

[Marcozi]

Convert it to a 6 speed manual!

 

[clinebarger]

Check Pin #3 at the Trans Plug for a Ground in Park/Neutral, This is the circuit that tells the ECM if the trans is in P/N.

Wire color is Orange with a Black Tracer.

 

[lookman23]

Hi there, have you solved the issue Nate ? got almost the same problem and hoped you've found the solution...