P0736-GEAR RATIO ERROR IN REVERSE

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 P1736).

2) An excessive change in input or output speeds indicating signal intermittent may 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
CUT L/R TOWER SEAL ON MAIN VALVE BODY
CUT L/R CLUTCH PISTON SEALS
BROKEN OR MISSING L/R CLUTCH BLEED ORIFICE (IN L/R CLUTCH RETAINER)
CUT L/R ACCUMULATOR PISTON SEAL IN MAIN VALVE BODY
CRACKED L/R ACCUMULATOR PISTON IN MAIN VALVE BODY
CUT OD/REV PISTON SEALS
BROKEN OR MISSING OD/REV BLEED ORIFICE (IN OD/REV CLUTCH PISTON)
BROKEN REVERSE CARRIER HUB WELD
BROKEN REVERSE SUN GEAR WELD TO THE 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 DTC's

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

Yes


No

2. CHECK IF DTC IS CURRENT

With the scan tool, perform the Reverse Gear Clutch test. Follow the instructions on the scan tool.
Increase the throttle angle, TPS degree, to 30 degrees , for no more than a few seconds.

CAUTION: Do not overheat the transmission.


NOTE: Make sure to record all DTC 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


No

3. CHECK DTC EVENT DATA

The conditions necessary 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.

Does the DTC EVENT DATA show an input speed reading of zero?

Yes


No

4. POSSIBLE INTERNAL TRANSMISSION CAUSES

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

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


No

5. CLUTCH TEST FAILURE


Did the clutch test fail in reverse?

Yes


No

6. 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

7. CHECK REVERSE CARRIER HUB

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

Were there any problems found?

Yes


No

8. CHECK FOR INTERMITTENT OPERATION

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 Starter Relay.

CAUTION: Removal of the Starter Relay will prevent the vehicle from being started in gear.


WARNING: The Starter Relay must be removed from the PDC. Failure to do so can result in personal injury or death.


NOTE: Failure to remove the Starter Relay can cause a Transmission - No Response condition.


Check the Speed Sensor wiring and connectors for good connection, then perform a wiggle test using the Transmission Simulator, Miller tool #8333.

Were there any problems found?

Yes


No