P0729
P0729-GEAR RATIO ERROR IN 6TH
For a complete wiring diagram refer to Diagrams/Electrical. Electrical Diagrams
Theory of Operation
The transmission system uses two speed sensors, one to measure input rpm and one to measure output rpm. These inputs are essential for proper transmission operation. Therefore, the integrity of this data is verified through the following checks:
NOTE: Various Gear Ratio Error DTCs will set only if the transmission slips after first achieving the correct ratio. Therefore, a transmission with no drive (or reverse) may not set any Gear Ratio Error DTC because it never achieves a correct gear ratio.
1) Once in a particular gear, if the gear ratio varies from the correct gear ratio, the corresponding in-gear trouble code is set (DTCs P0729 and P0731-36).
2) An excessive change in input or output speeds indicating signal intermittent will result in the DTCs P0716 and/or P0721 being set.
3) If the common speed sensor ground circuit is lost, both sensor inputs will read the pulses from the input speed sensor when at a stop in neutral. Since the input speed sensor reads 60 teeth from the input clutch hub and the output speed sensor reads 30 teeth from the park gear, the result is an apparent speed ratio of 1:2 and may cause the DTC P1794 to set.
- When Monitored:
Continuously with the ignition on, engine running, with the transmission in gear.
- Set Condition:
If the ratio of the Input rpm to the Output rpm does not match the current gear ratio. This DTC can take up to five minutes of problem identification before illuminating the MIL.
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. 68RFE Pre-Diagnostic Troubleshooting Procedure
Diagnostic Test
1. CHECK FOR RELATED DTCS
With the scan tool, check for other transmission DTC's
If any of these DTCs are present, perform their respective tests first.
Are there any Transmission; solenoid, line pressure, speed sensor, and/or loss of prime DTCs present?
Yes
- Refer to the Transmission category and perform the appropriate symptom. If any of these DTCs are present, they may cause a Speed Ratio Error. Perform the test for P0944 first if it is present. P0944
No
- Go To 2
2. CHECK DTC EVENT DATA
With the scan tool, read and record the DTC EVENT DATA.
NOTE: Make sure to record all DTC EVENT DATA stored in the scan tool for future reference in this test procedure.
Does the DTC EVENT DATA display information for the DTC P0729?
Yes
- Go to 4
No
- Go to 3
3. CHECK THE TARGET GEAR
In the DTC EVENT DATA recorded earlier, does the DTC EVENT DATA show the DTC P1790, with Target gear = 6th, or with both the 2C and OD clutches applying?
Yes
- Go to 4
No
- Go to 6
4. CHECK INPUT RPM
In the DTC EVENT DATA recorded earlier, does the Input rpm read zero?
Yes
- Refer to the Transmission category and perform the diagnostic procedure for P0716-Input Speed Sensor Circuit Performance. Diagnose the DTC as if it is set and current. P0716
No
- Go to 5
5. CHECK LINE PRESSURE READING
In the DTC EVENT DATA recorded earlier, is the line pressure reading more than 10 psi below the desired line pressure reading?
Yes
- Remove the Transmission Oil pan and check the Transmission Oil filter for improper installation or plugged, if Primary oil filter is OK, check the main regulator valve in pump. If excessive debris is in the oil pan, check clutches and repair as necessary.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test
No
- Go to 6
6. CHECK TRANSMISSION FOR SLIPPAGE
Erase DTCs and road test the vehicle.
Check the transmission operation in reverse and all forward gears.
During the road test, was there any obvious slippage noted in any gear, or did the transmission fail to make a 1-2 upshift?
Yes
- Go to 8
No
- Go to 7
7. CHECK IF DTC RESETS
With the scan tool, check for Transmission DTCs after the road test.
Did the DTC P0729 reset?
Yes
- Go to 8
No
- Test Complete.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test
8. CHECK INTERNAL TRANSMISSION
Remove the Transmission Oil Pan and Valve Body,, and check for the following:
- Excessive clutch and or metal debris in the oil pan.
- If the accumulator cover is intact and the 2C tower seal is not cut or split.
- OD and 2C accumulator pistons for cracks or cut seals.
- Solenoid Switch Valve and its plugs for stickiness or wear.
- Cut or missing #5, #6, or #7 check ball.
- OD bleed orifice on top of the valve body.
- Air check the OD and 2C hydraulic clutch circuits for excessive leakage.
NOTE: Both the OD and 2C hydraulic clutch circuits contain a small bleed orifice. A small amount of air leakage is considered normal. The OD hydraulic clutch circuit bleed orifice connects to the Reverse input clutch hydraulic cavity. A small amount of air leakage into the Reverse hydraulic clutch circuit is considered normal.
Were there any problems found?
Yes
- Repair as necessary.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test
No
- Go to 9
9. CHECK ROAD TEST RESULTS
During the road test, were Reverse, 1st, 2nd, and 3rd gears OK, but the transmission slipped in 4th, 5th, and 6th gears?
Yes
- Go To 10
No
- Go To 11
10. CHECK THE OD SHAFT AND REVERSE CARRIER SPLINE
Remove the Transmission and inspect the OD shaft and its spline to the reverse carrier hub.
Were there any problems found?
Yes
- Repair as necessary.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test
No
- Disassemble and inspect the input clutch assembly. Check the OD and Reverse clutch seals, discs, and bleed orifice (in the OD/Reverse clutch piston) and repair as necessary.
NOTE: If the OD clutch has failed but no obvious cause is found (such as a cut piston seal, broken seal ring, low line pressure in DTC Event Data, etc.), replace the Transmission Solenoid/TRS Assembly in addition to any other necessary repairs.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test
11. CHECK FOR FAILED REVERSE GEARSET SPLINES
Working through the windows in the bottom of the case, check for a failed Reverse Sun or Annulus gear spline as follows:
1) Hold the Transmission Output Shaft by holding the Transmission Manual Lever in the park position.
2) Apply the 4C clutch using 30-40 psi shop air at the apply port in the center bulkhead.
3) Attempt to rotate the input annulus gear and drive shell (the drum that encloses the two rearmost gearsets).
NOTE: Due to the overrunning clutch, the gear and drive shell normally rotates in one direction only.
Can the drive shell be rotated?
Yes
- Repair internal transmission as necessary. Check the reverse annulus gear spline to the input carrier, and the reverse sun gear spline to the reaction carrier hub.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test
No
- Replace Transmission Solenoid/TRS Assembly and Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test
NOTE: If continued slippage is noted in 2nd and/or 6th gear during the verification test, remove the transmission and inspect the 2C clutch and repair as necessary.