Have you ever been somewhere, met someone, or seen a scenario play out that you would swear you had previously experienced? Or maybe in your mind, you are confused as what you are experiencing seems so familiar, but you just can’t put a finger on the experience. If you are like me, it may have happened to you numerous times throughout your life, and it feels like you are watching the movie Groundhog Day.
In the last few months, I have had several shops indicate that they had a late model 6L series transmission exhibiting a “no forward” concern, and they are curious if I had seen the issue. The first one, several months back, was a 2022 Silverado with 30K miles. As I was standing there visiting with the technician, I knew I had seen this issue before, but my mind was blank as I could not remember the solution to the concern. As one gets older, you have to learn patience, as it takes a while for the old brain to kick into gear. After about an hour of working with them on other issues, the old brain kicked back in gear, and I remembered what I was trying to remember: check ball #1 may be having some issues. But how could that be? The issue had been addressed by GM more than ten years earlier. If check ball #1 (Figures 1 and 2) is having issues, the 6L45 (RPO MYA), 6L50 (RPO MYB), 6L80 (RPO MYC), 6L90 (RPO MYD) may exhibit any of the following symptoms:
No forward or slips when moving forward or falls out of gear (neutral) during operation when the transmission is cold while in first gear.- Possible P2723 (Solenoid #5 stuck off) and/or P2724 (Solenoid #5 stuck on) may be set. Many times, DTCs are not associated with this issue, but it is possible that the DTCs were set prior to the ball completely failing. It is really easy to get confused regarding what is causing your concern, as many solenoid/TEHCM issues or low one-way clutch failures can also cause a “No Forward” related issue. Since the check ball can also cause the issue, it is important that you inspect the check ball before ordering a TEHCM or ripping the transmission apart to gain access to the low one-way clutch.
These conditions may be intermittent in nature:
- The #1 check ball may be stuck in the plate, worn, or even missing. Typically, we see the ball decreasing in size from .250” to .180” or less and getting stuck in the plate or in some instances, blowing right through the plate.
- The #1 check ball is in the upper valve body and part of the 1-2-3-4 clutch circuit. Drive 1-6 fluid seats the ball against the spacer plate, then enters the 1-2-3-4 clutch feed circuit to apply the 1-2-3-4 clutch for 1st gear.
P2723 and P2724 are ratio error DTCs and will set if:
DTC P2723
- DTC P0101–P0103, P0106–P0108, P0171, P0172, P0174, P0175, P0201– P0208, P0300–P0308, P0401, P042E, P0716, P0717, P0722, P0723, P18BA−P182F, P18C0−P18C3, P1915, P2534 = Not set
- Accelerator Pedal Position Sensor = Greater than 0.5%
- Accelerator pedal position signal = Valid
- Engine Speed = 400 to 7,500 RPM
- High Side Driver = Enabled
- Ignition Voltage = 9 to 32 V
- Internal Mode Switch ≠ Default
- Transmission Output Speed = Greater than 67 RPM
- Transmission Fluid Temperature = Warmer than −6.6°C (20.1°F)
- The 1-2-3-4 clutch gear ratio is incorrect
- The above conditions occur 3 times
If P2723 is set, the TCM will:
- Request reduced engine torque based on transmission input speed.
- Command maximum line pressure.
- Freeze transmission adaptive functions.
- Inhibit grade braking.
- Inhibit neutral idle.
- Inhibit Manual Up/Down Shift with the shift selector.
- Inhibit TAP Up/Down function.
- Inhibit Tow/Haul mode.
- Limit the transmission to Reverse gear and 5th gear operation.
DTC P2724
- DTC P0101–P0103, P0106–P0108, P0171, P0172, P0174, P0175, P0201– P0208, P0300–P0308, P0401, P042E, P0716, P0717, P0722, P0723, P18BA−P182F, P18C0−P18C3, P1915, P2534 = Not set
- 1-2-3-4 Clutch = Commanded Off
- Commanded gear = 1st Gear
- Transmission Input Speed = Greater than 150 RPM
- Transmission Output Speed = Greater than 100 RPM
If P2724 is set the TCM will:
- Request reduced engine torque based on transmission input speed.
- Command maximum line pressure.
- Freeze transmission adaptive functions.
- Inhibit grade braking.
- Inhibit neutral idle.
- Inhibit Manual Up/Down Shift with the shift selector.
- Inhibit TAP Up/Down function.
- Inhibit Tow/Haul mode
- Limits the transmission to 2nd gear if the output speed sensor signal is less than 1,400 RPM. No upshift will occur.
- Limits the transmission to 4th gear if the output speed sensor signal is 1,400 RPM or greater.
If the ball fails to seal properly, the clutch pressure will be allowed to exhaust at the clutch select #2 valve, leading to 1-2-3-4 clutch apply issues. The check balls are “wearing “as the turbulence in the valve body ball pocket causes ball rotation, and the “soft” ball material is subject to wear. Even though the ball looks good, it may be too small to properly seal the hole in the spacer plate. Remember to replace ALL of the check balls when performing an overhaul or valve body service on a 6L45/6L50/6L80/6L90.
Well, sure enough, the ball on the 6L80 in question had blown through the spacer plate, so there was no way the 1-2-3-4 clutch could apply. When the OEM addresses issues, one does not expect to see the same cause for the same concern ten years later, but we have to remember that staffing at the OEM engineering level changes constantly. The new folks may not know what happened in the distant past, so it is possible to see the same mistake repeated down the road, “what is old is truly new again.” It is sad, but it is the reality that we live in today.
Until next time, remember, “History repeats itself, and that’s one of the things that’s wrong with history.”
