P0734-GEAR RATIO ERROR IN 4TH

For a complete wiring diagram Refer to Section 8W

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:

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 P01736).

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.



Possible Causes
LOW FLUID LEVEL
INPUT SPEED SENSOR OR WIRING
VALVE BODY ACCUMULATOR COVER FAILED
CUT OD OR 4C ACCUMULATOR SEAL
CRACKED OD OR 4C ACCUMULATOR PISTON
BROKEN OR MISSING OD BLEED ORIFICE IN MAIN VALVE BODY
CUT 4C TOWER SEAL
TRANSMISSION SOLENOID/TRS ASSEMBLY
CUT OR MISSING #5 OR #6 CHECK BALL
WORN SOLENOID SWITCH VALVE OR PLUGS
CUT OD OR 4C PISTON SEAL
STUCK MAIN REGULATOR VALVE
BURNED OD OR 4C CLUTCH
BROKEN OR MISSING 4C BLEED ORIFICE IN 2C/4C RETAINER
BROKEN REACTION SHAFT SUPPORT SEAL RING
POOR MACHINING ON PUMP VALVE BODY FACE
LOOSE / MISSING DRIBBLER ORIFICE ASSEMBLY IN REACTION SHAFT SUPPORT
CRACKED / LOOSE / MISSING OD/REVERSE PISTON BLEED ORIFICE
BROKEN REVERSE CARRIER HUB WELD
BROKEN REVERSE SUN GEAR WELD TO REACTION CARRIER

Always perform the 45RFE/545RFE Pre-Diagnostic Troubleshooting Procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD 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


No

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 P0734?

Yes


No

3. CHECK FOR ANOTHER DTC


In the DTC EVENT DATA recorded earlier, does the DTC EVENT DATA show the DTC P1790, with Target Gear = 4th, or with both the 4C and OD clutches applying?

Yes


No

4. CHECK INPUT RPM


In the DTC EVENT DATA recorded earlier, does the Input rpm read zero?

Yes


No

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


No

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 4th gear or a runaway during the 3-4 shift?

Yes


No

7. CHECK IF DTC RESETS

With the scan tool, check for Transmission DTCs after the road test.

Did the DTC P0734 reset?

Yes


No

8. CHECK INTERNAL TRANSMISSION

Remove the Transmission Oil Pan and Valve Body per the Service Information and check for the following:

NOTE: Both the OD and 4C 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


No

9. CHECK REVERSE GEAR


Was there no reverse gear during the road test?

Yes (no reverse)


No (reverse gear OK)

10. CHECK ROAD TEST RESULTS


During the road test, was there no 2nd gear and no 4th gear, but 3rd gear (limp-in) was OK?

Yes


No

11. CHECK FOR BROKEN REVERSE SUN GEAR WELD

Working through the windows in the bottom of the case, check for a broken Reverse Sun gear weld to the reaction carrier as follows:
1) Hold the Transmission Output Shaft by holding the Transmission Manual Lever in the park position.
2) Rotate the Input Annulus gear and drive shell (the drum that encloses the two rearmost carriers).
3) 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


No

12. CHECK REVERSE CARRIER HUB WELD

Remove the Transmission per the Service Information and inspect the weld on the reverse carrier hub.

Were there any problems found?

Yes


No