Issue Summary:
- An Isuzu with a 4L30-E may go into failsafe, with solenoid codes stored, after a fluid-and-filter change.
- After overhaul, an Isuzu or BMW vehicle with a 4L30-E may partially stall when the transmission is placed into gear or may exhibit discoloring and/or premature failure of the torque converter.
- After overhaul, vehicles equipped with the Mercedes 722.6 transmission may exhibit multiple gear-ratio errors and/or limp mode.
The vehicle comes in for a fluid change, and after the fluid change is completed, the transmission is in failsafe; in some instances the TCM is found to be faulty. None of these complaints existed before the fluid change.
The internal wire harness in the main valve-body area, where the filter is situated, is encased in a plastic conduit (Figure 1) that hardens over time.
When the new filter is installed, it can be pushed up against the wire harness (Figure 2), causing the conduit to break up in sections.
This can expose a wire splice in the internal harness, causing it to come into contact with the valve body and resulting in a short to ground (Figure 3), which causes the complaints mentioned.
The type of failure that will occur depends on the year of the vehicle. 1990-1993 vehicles are equipped with a Bosch TCM, which controls the solenoids on the power side. A short causes solenoid codes to store and a failsafe condition.
1994 and later vehicles are equipped with a Delco TCM, which controls the solenoids on the ground side. In addition to solenoid codes and failsafe, a short here will more than likely destroy the solenoid driver, which will require TCM replacement.
As a side note, this transmission is also in some BMW models as well as the Cadillac Catera. The solenoids in these vehicles are controlled on the ground side. Therefore, it is possible to have the same TCM failure.
After overhaul, 2000 and up vehicles equipped with the 4L30-E transmissions may exhibit a partial stalling condition when the vehicle is placed into gear, or discoloring and/or premature failure of the torque converter, with an eventual P1870 code, TCC slip.
The cause may be that during bushing installation, a THM 350 bushing was used and was placed too deep into the bellhousing, as shown in Figure 4.
When this happens, and the torque-converter clutch is commanded off, the bushing will partially block the “to cooler” passage, which will act as a cooler restriction, creating the partial engine stall. See Figure 5 for a partial hydraulic-circuit diagram of TCC off. When the torque-converter clutch is commanded on, the converter-apply circuit is restricted, creating low apply pressure and premature torque-converter failure as well as discoloring of the torque converter.
Refer to Figure 6 for a partial hydraulic circuit of TCC on.
Refer to figures 4 and 7 to see the dimensional difference between the Sonnax bushing and the THM 350 bushing and to identify the previously mentioned passage in the bellhousing.
One other cause may be a partially stuck converter-clutch control valve (Figure 8).
Note: The hydraulic-circuit diagrams and pump references are for the versions with the four-valve pump; Passport, Rodeo and Catera do not have this version of pump.
Replace the bushing with the Sonnax bellhousing bushing, or when using a THM 350 bushing use a die grinder to remove the excess material to ensure no restrictions in the passage shown in figures 4 and 7.
Refer to Figure 8 and ensure that the converter-clutch control valve is not sticking in the pump.
- Sonnax bellhousing bushing. . . . . . . . . . . 54253-01
After overhaul, vehicles equipped with the 722.6 transmission may exhibit multiple gear-ratio errors and/or limp mode.
The cause may be that during overhaul incorrect planetary assemblies were used, creating incorrect gear ratios based on the programming in the vehicle’s computer.
Verify the correct part numbers, by VIN, for the planetary assemblies through the dealer, as ratios may change by engine size, differential ratio and engine performance. Refer to Figure 9 for a cross-sectional view of this transmission to locate the front, center and rear planetary assemblies.
Refer to Figure 10 for individual charts listing common tooth counts on typical V-8 and V-6 models and a chart for Sprinter and Freightliner models.
Note: Notice that there are V-8 models that have different ratios; be careful! Because of the many different models there are open spaces available in the charts for your input.
Figures 11-13 show possible tooth counts for the front, center and rear planetary assemblies.
September 2008 Issue
Volume 25, No. 9
- Isuzu 4L30-E: Solenoid codes stored with failsafe
- Isuzu & BMW 4L30-E: Partial engine stall/torque-converter failure
- Mercedes 722.6: Gear-ratio errors