2007 Commander XK Factory Service Manual 21 - TRANSMISSION AND TRANSFER CASE

P0734-GEAR RATIO ERROR IN 4TH

For a complete wiring diagram Refer to Section 8W



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 Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - DIAGNOSIS AND TESTING) .

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).

2) An excessive change in input or output speeds indicating signal intermittent may result in the DTCs P0715 and/or P0720 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.



Diagnostic Test

1. DETERMINING IF RELATED DTC'S ARE PRESENT

With the scan tool, check for other transmission DTC's
If any of these DTC's are present, perform their respective tests first.

Are there any Transmission; solenoid, line pressure, speed sensor, and/or loss of prime DTC's 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 OTHER 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 RESET

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:
— Excessive debris in the oil pan.
— Remove the Valve Body and check if the accumulator cover is intact and the 4C tower seal is not cut or split.
— OD and 4C accumulator pistons for cracks and/or cut seals.
— Solenoid Switch Valve and its plugs for stickiness or wear.
— Cut or missing #5 and/or #6 check ball.
— OD bleed orifice on top of the Valve Body
— Air check the OD and 4C hydraulic clutch circuits for excessive leakage. Refer to the Service information.

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. TRANSMISSION SOLENOID/TRS ASSEMBLY


Was there no reverse gear during the road test?

Yes


No

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 frontmost 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 FOR NO REVERSE

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

Were there any problems found?

Yes
  • Repair as necessary. Refer to the Service Information for proper repair procedures.


No