An older engineer used to tell me, “Kid, if you stay on the ship long enough, you will see the same sights over and over again.” When I was young, I really did not understand what he meant by the statement, but as I have aged, I learned exactly what he was referring to.
OEM suppliers and the OEM themselves seldom have an issue with only one vehicle, no matter what they may try to convince you of. So, when someone tells you they have never heard of the issue you are having, there is always a possibility that that statement may be true for that individual. But it is more than likely someone out there has already experienced the issue and may have already addressed that exact concern.
When products are mass-produced, processes are put into place to perform quality control inspections on the parts and processes used. Most of the time, that eye on quality will catch the issues that are occurring, but, on some occasions, issues will get past the spot check process and may ultimately end up in a dealer service department or your shop for repair.
When you first come across the issue it can be intimidating as you may have never seen that specific complaint on the type of unit you have sitting in your stall. GM, like other brands, seems to have issues running in spurts. You go a few months without seeing any issues, and then you get five in a row with the same complaint. This exact scenario happened this past week. A shop had a GM 10-speed, which showed up for a no reverse concern, and within a couple of days, another GM 10-speed showed up with a no reverse condition. Both applications were in Chevrolet Silverado’s with the now infamous L87 6.2L gasoline engine. Neither unit had reverse, and one had a DTC P2732 (Control Solenoid #6 Stuck Off) set. This issue can affect different GM 10L applications, including Transmission RPOs MI1, MI4, MHT, MI2, and MQB. Both of the units had been overhauled, and new valve bodies were installed. Within about 20K miles, the units were back with the complaint of no reverse. So, what could cause the issues? Both the P2732 and the no reverse conditions could be related, so let’s look at what it takes to set a P2732. P2732 control solenoid #6 stuck off will set if the following occurs:
- DTC P2534 is Not set
- DTCs related to the following system/components are Not Set
- B14A Automatic Transmission Output Speed Sensor
- B14C Automatic Transmission Input Speed Sensor
- B14DA Automatic Transmission Intermediate Speed Sensor 1
- B14DB Automatic Transmission Intermediate Speed Sensor 2
- B303 Transmission Range Sensor
- Transmission Control Solenoid Valves — Circuit DTCs
- Battery Voltage, Greater than 9 V
- Engine, Running
- High Side Driver 1 is On
- High Side Driver 2 is On
- Ignition and Start Signal, Greater than 9 V
- Ignition and Start Switch Signal, On
- Transmission Range indicates it is in gear
- One of the following conditions listed below is true:
- Accelerator Pedal Position = Greater than 0.5%
- Engine Speed = Greater than 1,000 RPM
- Transmission Input Speed = Greater than 349 RPM
- Transmission Output Shaft Speed = Greater than 35 RPM
- The 4-5-6-7-8-9-10-R Clutch is commanded, but it did not apply
Since we clearly have a ratio-related DTC, and we are missing gears related to a specific ratio, we have several areas to examine for the cause. Mechanical issues, hydraulic issues, or electrical-related issues can set this DTC. This means we have a lot to inspect, whether you have a DTC set or just simply the symptom of no reverse. These include:
- Speed sensor issues may not result in a speed sensor DTC setting but may result in ratio DTCs being set.
- Solenoid/circuit electrical issues may not result in a solenoid DTC setting but may result in ratio DTCs being set.
- Sticking, worn, damaged 4-5-6-7-8-9-10-R Clutch regulator valve.
- A damaged/worn/collapsed solenoid retaining clip or faulty solenoid
- 4-5-6-7-8-9-10-R Clutch leakage.
- A restricted clutch feed circuit (most likely a worn/damaged check ball).
As I stated earlier, do not be surprised when you see an issue repeated in a new unit that you may have seen in another transmission model or year. In this instance, remember the issues we had with the 6L applications with check ball wear leading to a no-forward movement condition? We saw that issue early on in the 6L due to the material the balls were made of. Just a couple of years ago, we saw the issue repeated, but this time, the spacer plate was the root cause of the ball wear.
The 10-speeds are suffering the same issue. The chamfer on the spacer plate holes where the balls seat may be too rough, leading to premature ball wear. This was ultimately the cause of concern for both of the 10L applications I refer to in this article (Figure 1).
That is the good news. The bad news is your symptoms, and possible DTCs may not be the same as I am describing above, as it depends on which ball is worn and whether the ball is stuck in the spacer plate hole or if the ball has blown all the way through the plate.
Just like the 6L applications, if the ball is worn, you will clearly see a difference in ball diameters. Well, that’s about all the time we have for now. Until next time, remember, “I don’t sell cars; I sell engines. The cars I throw in for free since something has to hold the engines in.” – Enzo Ferrari
