Powertrain Control Module (PCM) - 545RFE
P0736-GEAR RATIO ERROR IN REVERSE
Special Tools:
For a complete wiring diagram, refer to the Wiring Information.
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 P0731-36 and P1736).
2) An excessive change in input or output speeds indicating signal intermittent which 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, and after the transmission has achieved the proper gear ratio.
- 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. Pre-Diagnostic Troubleshooting Procedure.
1. CHECK FOR RELATED DTCs
1. Using the scan tool, check for other transmission DTCs.
Are there any Transmission solenoid, line pressure, speed sensor, and/or loss of prime DTCs present?
Yes
- Refer to DTC Based Diagnostics and perform the appropriate diagnostic procedure. Perform the test for P0944-LOSS OF PRIME first if it is present.
No
- Go To 2
2. CHECK IF DTC IS CURRENT
1. Using the scan tool, perform the Reverse Gear Clutch test. Follow the instructions on the scan tool.
2. Increase the throttle angle, TPS degree, to 30°, for no more than a few seconds.
CAUTION: Do not overheat the transmission.
NOTE: Make sure to record all Event Data stored in the scan tool for future reference in this test procedure.
Did the clutch test pass, input speed remain at zero?
Yes
- Go To 3
No
- Go To 4
3. CHECK EVENT DATA
1. The conditions necessary to set this DTC are not currently present.
2. Using the scan tool, check the Event Data to help identify the conditions in which the DTC was set.
Does the Event Data show an input speed reading of zero?
Yes
- Go To 8
No
- Go To 4
4. POSSIBLE INTERNAL TRANSMISSION CAUSES
1. Remove the Transmission Oil Pan and Valve Body and check the following:
- Clutch or metal debris in the pan
- L/R clutch tower seal on the main valve body for cuts and the L/R accumulator piston and seals.
- Air check the Reverse and L/R Hydraulic Clutch circuits (in the case) for excessive air leakage.
NOTE: Both Hydraulic Clutch circuits contain a small bleed orifice , a small amount of air leakage is normal. The Reverse hydraulic clutch circuit bleed orifice connects to the OD hydraulic clutch cavity. A small amount of air leakage into the OD hydraulic clutch circuit is considered normal.
Were there any problems found?
Yes
- Repair as necessary. If clutch debris is present, remove the transmission and inspect the Reverse and L/R clutches, and inspect the Transmission Oil Pump and Main Regulator Valve for damage or sticking in its bore.
NOTE: If the L/R clutch has failed but no obvious cause is found (such as a cut piston seal, stuck regulator valve, low line pressure reading in the Event Data, or any other items listed above) replace the Transmission Solenoid/TRS Assembly in addition to any necessary internal repairs.
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. 545RFE Transmission Verification Test
No
- Go To 5
5. CLUTCH TEST FAILURE
Did the clutch test fail in reverse?
Yes
- Go To 6
No
- Test complete.
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. 545RFE Transmission Verification Test
6. CHECK FOR BROKEN REVERSE SUN GEAR WELD
1. Working through the windows in the bottom of the case, check for a broken Reverse Sun gear weld to the reaction carrier as follows:
- Hold the Transmission Output Shaft by holding the Transmission Manual Lever in the park position.
- Rotate the Input Annulus gear and drive shell, (the drum that encloses the two rearmost carriers).
- Check to see if the reaction carrier (the front-most carrier, whose outer shell is splined to the 2C clutch) is rotating faster than the drive shell is being turned.
Is the reaction carrier turning faster than the drive shell?
Yes
- Go To 7
No
- Replace the reaction carrier.
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. 545RFE Transmission Verification Test
7. CHECK REVERSE CARRIER HUB
1. Remove the Transmission and inspect the weld on the reverse carrier hub.
Were there any problems found?
Yes
- Repair as necessary. Refer to the proper repair procedures.
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. 545RFE Transmission Verification Test
No
- Disassemble and inspect the input clutch assembly. Check the Reverse clutch reaction plate snap ring. Check the OD and Reverse clutch seals, discs, and bleed orifice (in the OD/Reverse clutch piston). Check the Reverse hub and shaft. Repair as necessary. Refer to the proper repair procedures.
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. 545RFE Transmission Verification Test
8. CHECK FOR INTERMITTENT OPERATION
1. Intermittent gear ratio DTCs can be set by problems in the Input and Output Speed Sensor circuits and/or Speed Sensor Ground circuit.
2. 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 possible serious or fatal injury.
3. Install the Transmission Simulator.
4. Check the Speed Sensor wiring and connectors for good connection, then perform a wiggle test using the Transmission Simulator.
Were there any problems found?
Yes
- Repair as necessary.
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. 545RFE Transmission Verification Test
No
- Test complete.