40TE GPEC
P0736-GEAR RATIO ERROR IN REVERSE
Theory of Operation
The Powertrain Control Module (PCM) 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 data checks. When in gear, if the gear ratio does not compare to a known gear ratio, the corresponding gear ratio error trouble code is set. The transmission will go into Limp-in mode after four gear ratio error events occur in a given driving cycle.
- When Monitored:
The Transmission gear ratio is monitored continuously while the transmission is in gear.
- Set Condition:
If the ratio of the Input RPM to the Output RPM does not match the current gear ratio when compared to the known gear ratio.
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.
1. DETERMINING IF RELATED TRANSMISSION DTCS ARE PRESENT
1. With the scan tool, read DTCs.
2. If any of these DTCs are present, perform their respective tests first.
Are there any Loss of Prime, Line Pressure and/or Speed Sensor DTCs present?
Yes
- Testing and Inspection Perform the appropriate diagnostic procedure. If any of these DTCs are present, they will cause a gear ratio error. Perform the test for Loss of Prime first if it is present.
- Perform the appropriate TRANSMISSION VERIFICATION TEST. Verification Tests.
No
- Go To 2
2. CHECK TO SEE IF THE DTC IS CURRENT
1. With the scan tool, perform the Reverse gear clutch test. Follow the instructions on the scan tool.
2. 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
- Repair internal Transmission. and repair or replace as necessary.
- Air check the Reverse and LR clutch passages for excessive leakage.
- Check all of the components related to the Reverse and LR clutches, and the front planetary gearset.
- Check the LR accumulator piston and seals.
- Check that the main regulator valve moves freely in its bore.
- If the LR clutch is burned but no cause is evident (such as a cut piston seal, cracked sump filter, stuck regulator valve, etc.) replace the solenoid/pressure switch assembly.
- Inspect the Transmission Oil Pump.
- Inspect the input shaft and reverse clutch hub (including the weld to the front sun gear).
- Perform the appropriate TRANSMISSION VERIFICATION TEST. .
3. CHECK FOR INTERMITTENT OPERATION
1. The conditions to set this DTC are not current at this time.
2. Check the gearshift linkage adjustment.
3. Gear ratio DTCs can be set by problems in the Input and Output Speed Sensor circuits. If the vehicle passes the Clutch Test and still sets Gear Ratio DTC, check the Speed Sensors for proper operation.
4. Turn the ignition off to the lock position.
5. Remove the Starter Solenoid Relay from the TIPM.
CAUTION: Removal of the Starter Solenoid Relay from the TIPM will prevent the vehicle from being started in gear.
WARNING: The Starter Solenoid Relay must be removed from the TIPM. Failure to do so can result in personal injury or death.
6. Check the wiring and connectors for the Speed Sensors for a good connection, then perform a wiggle test using the Transmission Simulator 8333A and the Electronic Transmission Adapter kit.
7. This DTC can also be set under extreme temperature conditions, this is usually caused by an internal problem. Verify if the problem is only experienced under extreme hot or cold conditions.
8. With the scan tool, check the Event Data to help identify the conditions in which the DTC was set.
9. Check for Service Information Tune-ups or Service Bulletins for any possible causes that may apply.
Were there any problems found?
Yes
- Repair as necessary.
- Perform the appropriate TRANSMISSION VERIFICATION TEST. Verification Tests.
No
- Test Complete.