As continued from Gear Ratio Error Codes Slipping Away - Part 2 of 3
When a hydraulic/mechanical fault occurs with one of these solenoids (as mentioned earlier), the diagnostic process begins with checking the operation of the solenoid and its related valve(s).
Unlike the 6T70/75 version, the solenoids in the 6T30/40/45/50 TEHCM can be easily removed from the assembly for inspection, which would include the rubber sealing rings as well (Figure 8). Sources are becoming available to replace these solenoids separately should there be a failure without having to replace the entire TEHCM assembly. Hopefully that will work out well.
If the solenoid inspects well and its related regulating valve is functional, something is wrong inside the transmission.
General Motors provides detailed information for each of these codes. Circuit/System description, conditions for running the DTC, conditions for setting the DTC, actions taken when the DTC is set to name a few. It also provides Circuit/System Testing so the technician can quickly begin to separate whether his hydraulic/mechanical performance code is a minor or major repair.
Using PCSV2 as an example, if code(s) P0776 and/or P0777 has set and it has been determined that the solenoid is not the cause, it offers up the following suggestions:
1. Actuator feed limit valve compromising circuit supply fluid to the solenoids.
2. 3-5-R Regulator Valve sticking or stuck.
3. A check ball in the valve body not seating correctly
These would be considered a minor repair in that the transmission would not have to be removed to make the repair. But if these all check out, with the 6T40 series style transmission, it’s time to pull the unit and inspect the 3-5-R clutch assembly. If it were the 6T70 series type transmission, there is a rear cover that can be pulled to give these clutches a look (Figure 9). Not so with the 6T40 unit. It all needs to come apart as the 3-5-R clutch drum assembly is located at the rear of the case (Figure 10). The sealing rings on the ring tower in the bottom of the case would need to be looked at. The drum area where the rings seal would need to be inspected for grooving (Figure 11). And then of course the clutch assembly itself including the apply piston (Figure 12).
As you can see, moving away from gear ratio codes to solenoid performance codes has actually simplified the diagnostic process. This example was with a compact little 6-speed transmission using five clutch pack assemblies. Compact transmission designs with minimal clutch pack assemblies also assists in simplifying diagnostics. With 9-speed transmissions already on the road today, the ones that have most of their solenoids doing the majority of the grunt work along with fewer valves in the valve body is a welcomed design diagnostically.
What is actually becoming complicated and very difficult to deal with is programming. It is mind boggling to think of all that is involved in writing a program to make just one shift under various loads, speed and temperature in conjunction with ABS, engine torque management, fuel economy and emissions. Now times that by nine shifts, which includes skip shift technology, sport and economy modes, and we can see how easily programming can become a problem. So the less we need to contend with when it comes to the transmission itself, the better. Part of the diagnostic process when it comes to programming, it is always a good idea to check for any factory TSBs for any re-flash updates related to your specific or related fault code.
This was a 3 part series article packed with information that is more than useful.
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