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68RFE Automatic Transmission






P0731-GEAR RATIO ERROR IN 1ST

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 DTCs.

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 IF DTC P0731 IS CURRENT

With the scan tool, perform the 1st Gear Clutch Test. Follow the instructions on the scan tool.

Increase the throttle angle or TPS Degree to 30� for no more than a few seconds.


CAUTION: Do not overheat the transmission.

Did the Clutch Test pass, Input Speed remain at zero?

Yes

- Go To 3

No

- Go To 4



3. CHECK FOR INTERMITTENT OPERATION

The conditions to set this DTC are not currently present.

With the scan tool, check the DTC EVENT DATA to help identify the conditions in which the DTC was set.
- If the DTC Event Data shows fault P0731 was set in Park, Reverse, or Neutral, replace the Powertrain Control Module.
- If the DTC Event Data shows fault P0731 set with input rpm = zero, check the input speed sensor and related wiring.
- If the DTC Event Data shows fault P0731 set with line pressure significantly below desired line pressure, check for the cause of low line pressure (i.e., oil level, mis-installed or damaged primary filter or filter seal, sticking main regulator valve in pump, etc.).
- If the DTC Event Data shows fault P0731 set with the UD pressure switch open (but line pressure matches Desired Line Pressure), air check the UD hydraulic clutch circuit for leakage. If the UD hydraulic clutch circuit is OK, replace the solenoid/TRS assembly.

Check the gearshift linkage adjustment.

Intermittent Gear Ratio DTCs can be set by problems in the Input and Output Speed Sensor circuits and/or Speed Sensor Ground circuit.

Remove the Ignition Switch Feed fuse from the TIPM.


CAUTION: Removal of the Ignition Switch Feed fuse from the TIPM will prevent the vehicle from being started in gear.


WARNING: The Ignition Switch Feed fuse must be removed from the TIPM. Failure to do so can result in personal injury or death.

Install the Transmission Simulator, Miller tool #8333.

Wiggle wiring and connectors while checking for intermittent operation with the Transmission Simulator.

Gear ratio DTCs can also be set under extreme temperature conditions.

Verify if the problem is only experienced under extreme hot or cold conditions.

Were there any problems found.

Yes

- Repair as necessary.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test

No

- Test Complete.



4. CHECK INTERNAL TRANSMISSION

Repair internal transmission as necessary.

If there were any line pressure DTCs present along with this DTC, make sure to inspect the: Primary oil filter and seal, Transmission Oil Pump, and the Main regulator valve.

If DTCs P0876 and/or P0875 were present in addition to the P0731, replace the Transmission Solenoid/TRS Assembly in addition to necessary internal repairs.

Pay particular attention to the following list of possible causes when repairing the transmission:
- Cut UD piston seal
- Failed overrunning clutch
- Burned UD clutch
- Cut UD accumulator seal ring
- Broken UD accumulator piston
- Low line pressure
- Broken/missing main valve body bleed orifice
- Broken/missing dribbler orifice assembly in reaction shaft support
- Poor machining on pump valve body face
- Transmission Solenoid/TRS Assembly

View repair

Repair

-
NOTE: If the UD 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 necessary internal repairs.
Repair internal transmission.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test
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