SIL 26-WT-23
January 02, 2024
Page 1 of 7
SUBJECT:

P2789 Transmission Clutch Life Expired for C3 and/or C5 Clutch — Troubleshooting and Repair
Procedure

MODELS AFFECTED:

3000 SeriesTM and 4000 SeriesTM TIDA and TIDB Transmissions with 4th, 5th and 6th
Generation Controls

Description of Complaint:
The Check Transmission lamp may illuminate along with setting DTC P2789 Transmission Clutch Life Expired
(Clutch Adaptive Learning at Limit) for C3 and/or C5 only. The Wrench Icon may show on the shift pad.
The C3 and C5 clutches may have disproportionately low clutch life when compared to all other clutches in the
prognostic tab in Allison DOC®. Refer to Figure 1. Customers may experience shift complaints with delayed and/or
harsh downshift related to PCS3 on-coming and off-going clutches. Shift complaints may include downshifts from
2-1 and upshifts from 2-3 and 4-5 on 6-speed models. If you believe the customer complaint exhibits one or more
of the symptoms, follow the troubleshooting steps to identify if the solenoid valve body is the cause.
NOTE: If prognostics is not enabled, DTC P2789 will not set. The concern may only present itself with the
shift complaints listed above.

Cause:
In high shift density applications, the transmission solenoid valve body can produce a pressure leak through the
PCS3 bore caused by wear to the PCS3 valve bore.

Service Channel Procedure:
CAUTION: TCM replacement, Recalibration or Clearing adaptive shifts will erase current Clutch life
data. If this has been done, reference the expired Clutch history section below the Transmission Health
Monitor for expired clutches for C3 or C5.
The following procedure outlines how to troubleshoot and repair if the issue is related to the solenoid valve body.

DH, RC / SL9161EN

6659287

Copyright © 2023 Allison Transmission, Inc. All Rights Reserved.

SIL 26-WT-23
January 02, 2024
Page 2 of 7
1. Review Allison DOC Prognostics Details
a. Connect to Allison DOC and confirm that DTC P2789 is active in the failure records and/or that C3 and
C5 clutches have disproportionately low clutch lives compared to the other clutches. Refer to Figure 1.

Figure 1. Prognostics Section
2. Measure Clutch Pressures
a. Set parking brake and chock the wheels.
b. Install clutch pressure gauges on Main, C3 and C5 diagnostic pressure ports.
c. Operate transmission to attain a transmission fluid temperature of 200°F (93°C).
NOTE: It is OK to stall test the unit briefly to attain fluid temperature of 200°F (93°C).

d. Connect with Allison DOC.
e. Using the Allison shift selector, shift the transmission into R (Reverse) range and measure actual
main pressure, C3 pressure and C5 pressure with the installed clutch pressure gauges. Record the
pressures in the Clutch Pressure Worksheet shown in Table 1.
f. Using Allison DOC, select the “Action request” drop down menu then select “Clutch Test Enabled” via
Allison DOC, refer to Figure 2. Once in Clutch Test, select 3rd Range and enable “Full Main Pressure”.
Measure actual main pressure and C3 clutch pressure with the installed gauges. Record the pressures
in the Clutch Pressure Worksheet shown in Table 1.

Copyright © 2023 Allison Transmission, Inc. All Rights Reserved.

SIL 26-WT-23
January 02, 2024
Page 3 of 7

Figure 2. Clutch Test
NOTE: C5 clutch logic will limit clutch pressure to C5 in neutral and first range. Pressure differential
between C5 clutch and main pressure greater than 15 psi in these ranges is acceptable and does not
indicate a C5 clutch pressure loss concern. Reference SIL 06-WT-18.

Table 1.
*Transmission fluid temperature at or above 93C/200F @ idle and "Full main pressure" in 3rd range*
Prior to Solenoid Valve Body Replacement
Reverse (Shift Selector) PCS2
controls C3 clutch

3rd range (Clutch Test Mode "Full main
pressure") PCS3 controls C3 clutch

Main Pressure
(kPa/psi)
C3 Clutch Pressure
(kPa/psi)
Pressure Differential =
Main Pressure minus C3
Clutch Pressure

g. Analyze results of clutch pressure test.
– Compare the pressure differences from actual Main pressure and C3 pressure in reverse and
third range.
– If pressure loss between Main and C3 is less than 15 psi in Reverse range and less than 15 psi in
third range, follow the troubleshooting steps in TS8794 for DTC P2789.
– If pressure loss between Main and C3 is less than 15 psi in Reverse range and greater than 15
psi in third range, complete the following procedures to check piston seal integrity.
3. Piston Seal Integrity Test
Piston seal integrity test can be performed on stationary clutches (C3/C4/C5) via the clutch port on the main
case. Refer to Figure 3. The purpose of this test is to check for piston seal leakage, which could also be the
cause of low clutch pressure in C3 or C5 clutches.

Copyright © 2023 Allison Transmission, Inc. All Rights Reserved.

SIL 26-WT-23
January 02, 2024
Page 4 of 7

Figure 3. Main Housing Clutch Pressure Ports
a. Drain transmission fluid and save in a clean container for reuse.
b. Remove the control valve module and perform a piston seal integrity test.
c. Check C3 and C5 piston seals by fully applying air pressure with a rubber tipped blow gun with shop
air pressure at 120 psi or higher to the corresponding pressure port on the main case.
NOTE: A shop rag should be used to protect against oil blowback while applying and releasing air
pressure.
d. Listen for a solid clunk and minimal air leakage. Some air leakage may occur. If the piston seal is
leaking, you will hear an air rushing noise and no movement of the clutch plates, indicating that the
piston seal has failed.

Copyright © 2023 Allison Transmission, Inc. All Rights Reserved.

SIL 26-WT-23
January 02, 2024
Page 5 of 7

NOTE: C3, C4 and C5 piston should have a similar sound. If one piston sounds different than the other
pistons, it may indicate that there is a leak.
e. If a piston seal leak is determined, repair the piston seal. This will require transmission removal
for repair.
f. If no piston seal leak is present, continue with the repair procedures to install a new solenoid valve
body and grooved trim valves.
4. Repair Procedure
Suggested Parts List:
• Body Assembly, Solenoid Valve And Pin (Qty 1)
• Valve, Lockup Trim. Refer to SIL 06-WT-22. (Qty 1)
• Valve, Clutch Trim. Refer to SIL 06-WT-22. (Qty 4)
• Control Module Seal and Gasket Kit (Qty 1)
Refer to 3000 Series Service Manual (SM4013) and/or 4000 Series manual (SM4014) for complete Control
Valve Module rebuild instructions.
a. Place Control Module on workbench.
b. Remove Solenoid Valve Body.
c. Remove solenoids and discard PCS1, PCS2, PCS3, PCS4 and TCC trim valves and springs.
d. Install new grooved trim valves per SIL 06-WT-22 and new trim springs into a new Solenoid Valve Body.
e. Remove and inspect the diagnostic valve from the original Solenoid Valve Body. If there are no
visible signs of damage, transfer the diagnostic valve to the new Solenoid Valve Body. (If there are
visible signs of issue, or the valve does not freely float into the new Solenoid Valve Body, replace
the diagnostic valve.)
f. Install the Solenoids, Solenoid retainers, PS1 switch assembly and new Chimney seals onto the new
Solenoid Valve Body.
g. Install the Solenoid Valve Body to the Main Valve Body. Torque to the pattern shown in Figure 4.
Follow the 3-step torque sequence listed below.

Copyright © 2023 Allison Transmission, Inc. All Rights Reserved.

SIL 26-WT-23
January 02, 2024
Page 6 of 7

Figure 4. Main Valve Body Torque Sequence
Position

Part Number

Specification

1-12

11515310

M6 x 1.0 x 95

13, 14

11516059

M6 x 1.0 x 45

15, 16

11515309

M6 x 1.0 x 60

Solenoid Valve Body – Torque Sequence
1. Start with the center of the bolt pattern (1) and work outward in a circular sequence. Get all bolts
started, finger tight.
2. Continuing to work from center outward, tighten bolts to 50 percent of nominal torque, 5-6 N·m
(3-5 lb ft).
3. Continuing to work from center outward, to a final torque of 10-13 N·m (7-10 lb ft).
h. Reinstall Control Valve Module with new case to control valve module gasket.
i. Torque Control Valve Module to 51-61 N·m (38-45 lb ft).
j. Refill transmission with fluid.
k. Install clutch pressure gauges on Main, C3 and C5 diagnostic pressure ports.
l. Start engine, check for leaks and adjust fluid level as needed.

Copyright © 2023 Allison Transmission, Inc. All Rights Reserved.

SIL 26-WT-23
January 02, 2024
Page 7 of 7
m. Operate transmission to attain a transmission fluid temperature of 200°F (93°C).
n. Follow pressure check procedures from Step 2 to confirm that the pressure differential has been
resolved. Once repairs are complete, clutch pressure differences should not exceed 15 psi versus
main pressure.
*Transmission fluid temperature at or above 93C/200F @ idle and "Full main pressure" in 3rd range*
After Solenoid Valve Body Replacement
Reverse (Shift Selector) PCS2
controls C3 clutch

3rd range (Clutch Test Mode "Full main
pressure") PCS3 controls C3 clutch

Main Pressure
(kPa/psi)
C3 Clutch Pressure
(kPa/psi)
Pressure Differential =
Main Pressure minus C3
Clutch Pressure

5. Complete Repair
a. Once repair is complete, use Allison DOC to select the “Action request” drop down menu then select
“Reset Adaptive Shift Parameters”.
b. Select the “Prognostics” tab and verify Transmission Health Indicator – Percent Clutch life remaining is
100% for all clutches. Refer to Figure 5.

Figure 5. Prognostics Information
c. Test drive to adapt shifts and confirm DTCs and shift complaints, if any, have been resolved.

Copyright © 2023 Allison Transmission, Inc. All Rights Reserved.