A/T - 4T80-E Shift Concerns/Service Transmission Lamp ON
File In Section: 07 - Transmission/TransaxleBulletin No.: 01-07-30-009B
Date: February, 2002
TECHNICAL
Subject:
No Power on Heavy Acceleration or 1-2 Shift Concerns - Delays, Slips, Flares, DTC P0731 and/or DTC P0732 Set (Replace Transmission Fluid Pressure Switch Assembly or Lower Control Valve Body Assembly)
Models:
2000-2002 Cadillac DeVille, Eldorado, Seville
2001-2002 Oldsmobile Aurora
with Hydra-Matic 4T80-E Automatic Transmission (RPO MH1)
This bulletin is being revised to add the 2002 model year and to enhance the technical information. Please discard Corporate Bulletin Number 01-07-30-009A (Section 07-Transmission/Transaxle).
Condition
Some owners of the above vehicles with a Hydra-Matic 4T80-E transaxle may comment about no power on heavy acceleration or 1-2 shift concerns such as delays slips or flares Cadillac customers with the above models may comment that "Service Transmission" may display on the Driver Information Center (DIC). The technician will note that DTCs P0731 (Incorrect 1st Gear Ratio) and/or P0732 (Incorrect 2nd Gear Ratio) are set.
Cause
^ This condition may be caused by a leaking transmission fluid pressure (TFP) switch assembly (936) that intermittently indicates park/neutral while in drive, during a heavy throttle launch. The Powertrain Control Module (PCM) software will invoke torque abuse protection when park/neutral is indicated with a large throttle opening. Engine torque is then managed causing the transmission input speed to decrease. Since the gear ratio that is calculated is outside of the range of any known gears, a DTC P0731 or P0732 may set.
^ This condition may be caused by a stuck or sticky 1-2 shift valve. A slip condition will cause the input speed to be too high and therefore gear ratio to be higher than expected.
Correction
Before any repairs are attempted, follow these steps:
1. Perform a Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission. Refer to SI2000 (Document ID # 655766 or the Engine Controls subsection of the Service Manual.
2. Inspect the transmission cooling system for leaks and repair as necessary.
3. Perform the Transmission Fluid Checking Procedure. Refer to SI2000 (Document ID # 790947 or the Automatic Transaxle subsection of the Service Manual.
4. Install a Tech 2 scan tool.
5. Turn ON the ignition, with the engine OFF.
Important:
Before clearing the DTCs, use the scan tool in order to record the Failure Records. Use of the Clear DTC Info function erases the Failure Records from the PCM.
6. Record the DTC Failure Records on the hard copy of the repair order for future powertrain engineering investigation and/or Technical Assistance Center (TAC) usage.
7. Clear the DTCs.
8. Use the scan tool snap shot mode in order to record current gear, gear ratio and TFP switch.
Important:
The vehicle must Start from zero vehicle speed.
9. From a stop, accelerate the vehicle starting at 10%, 20%, 30% throttle angle, etc. up to wide open throttle (WOT) to about 96 km/h (60 mph). Do this maneuver several times.
10. Verify that a DTC P0731 or P0732 has been set. If DTC P0731 or P0732 has NOT reset during the above road test procedure, go to Step 14.
11. Observe and record (on the repair order), the gear ratio displayed in the Tech 2 failure record.
If the gear ratio is between 1.05:1 and 1.54:1, go to Step 12.
^ If the gear ratio is between 0.71:1 and 0.95:1, go to Step 12.
^ If the gear ratio is less than 0.65:1, go to Step 12.
^ If the gear ratio is greater than 3.11:1, go to Step 13.
^ If the gear ratio is between 2.23:1 and 2.87:1, go to Step 13.
^ If the gear ratio is between 1.71:1 and 2.02:1, go to Step 13.
12. The TFP switch assembly (936) should be replaced only after completing the above road test procedure and DTC P0731 or P0732 was reset. Use the appropriate Service Manual for the proper repair procedure for the vehicle being serviced.
13. The lower valve body assembly should be replaced only after completing the above road test procedure and a DTC P0731 or P0732 was reset. Use the appropriate Service Manual for the proper repair procedure for the vehicle being serviced.
14. If a DTC DOES NOT reset, it was likely that sediment temporarily restricted the operation of the 1-2 shift valve. This sediment is often exhausted into the lube oil and ends up deposited in the transmission pan or on the filter. No further action is necessary on the part of the technician.
Parts Information
Parts are currently available from GMSPO.
Warranty Information
For vehicles repaired under warranty, use the table.
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