Circuit Description
The transmission control module (TCM) uses input from the input speed sensor (ISS) and the output speed sensor (OSS) to determine gear ratios. The TCM then compares the known gear ratio to the calculated gear ratio for the current range.
DTC P0729 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0729 Incorrect 6th Gear Ratio
Conditions for Running the DTC
| • | DTCs P0716, P0717, P0721, P0722, P0875, and P0876 are not active. |
| • | The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts. |
| • | Output speed exceeds 200 RPM. |
| • | 6th range is selected and attained. |
Conditions for Setting the DTC
DTC P0729 sets when the calculated 6th range ratio, steady state, differs from the known 6th range ratio.
Action Taken When the DTC Sets
| • | The TCM illuminates the malfunction indicator lamp (MIL). |
| • | The transmission defaults to 4th range while diagnostic response is active. |
| • | If the shift selector is moved to NEUTRAL, the transmission will shift to NEUTRAL. |
| • | If the shift selector is moved to REVERSE, the transmission will shift to REVERSE, unless the transmission is compromised by a direction change, then the transmission will shift to NEUTRAL. |
| • | If the shift selector is returned to a forward range and the transmission is compromised by over-speeding or direction change, the transmission will lock in NEUTRAL. |
| • | DTC P0729 is stored in TCM history. |
| • | The TCM freezes shift adapts. |
| • | The TCM inhibits torque converter clutch (TCC) engagement. |
Conditions for Clearing the DTC
A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.
Diagnostic Aids
| • | Incorrect ratio codes typically indicate mechanical conditions with specific clutches, such as 2-6 clutch and 3-5-6-REVERSE clutch for 6th range. |
| • | Incorrect ratio code could indicate a hydraulically failed solenoid. Observe DTC information for the specific solenoid. |
| • | Clutch test mode can be used to measure stall speed. Observe turbine speed signal. If the turbine speed signal does not return to zero or rises during the stall test, a leak or obstruction in a specific clutch apply circuit could be present. |
| • | You may have to drive the vehicle in order to experience a condition. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests ignition voltage.
-
This step tests for turbine speed not remaining at zero in 6th range.
Step | Action | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 | Measure the transmission fluid level. Refer to Transmission Fluid Check . Is the transmission fluid level correct? | -- | Go to Step 3 | Go to Transmission Fluid Check |
Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data. Is the voltage within the specified range? | 9-18 V | Go to Step 4 | Go to DTC P0562 for low voltage or DTC P0563 for high voltage | |
4 |
Is speed sensor data erratic? | -- | Go to the appropriate speed sensor DTC | Go to Step 5 |
|
Notice: Refer to Transmission Stall Test Notice in the Preface section. Conduct a clutch test for 6th range. Refer to Clutch Test . Did turbine speed remain at zero? | -- | Go to Diagnostic Aids | Go to Step 6 | |
6 |
Is the fluid contaminated or excessive material found in the pan? | -- | Go to Step 7 | Go to Step 8 |
7 | Remove the transmission for overhaul or replacement. Refer to Transmission Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- |
8 | Inspect for a stuck or sticking pressure control valve. Refer to Control Valve Body Cleaning and Inspection . Did you find a valve condition and repair it? | -- | Go to Step 10 | Go to Step 9 |
9 | Replace pressure control solenoid 2 (PCS2). Refer to Control Valve Solenoid Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- |
10 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | Go to Step 11 | Go to Step 2 |
11 | With the scan tool, observe the stored information, capture info and DTC info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
