DTC P0734 Incorrect 4th Gear Ratio Diesel Only
| Table 1: | 4L80-E Range Reference, modified for DTCs P1870 & P1871 |
| Table 2: | DTC P0734 (Diesel) |
Range | Gear | 1-2 Sol | 2-3 Sol | Fourth Clutch | Overrun Clutch | O/D Roller Clutch | FWD Clutch | Direct Clutch | Front Band | Interm. Sprag Clutch | Interm Clutch | Lo Roller Clutch | Rear Band |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Overdrive | 1st | On | Off | -- | -- | H | A | -- | -- | * | -- | H | -- |
2nd | Off | Off | -- | -- | H | A | -- | -- | H | A | O | -- | |
3rd | Off | On | -- | -- | H | A | A | -- | O | A | O | -- | |
4th | On | On | A | -- | O | A | A | -- | O | A | O | -- | |
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Circuit Description
The powertrain control module (PCM) calculates a ratio based on the automatic transmission input shaft speed (A/T ISS) sensor and output shaft speed (OSS) sensor readings. The PCM compares the known transmission gear ratio to the calculated ratio, for the selected gear range.
If the PCM detects an incorrect gear ratio, then DTC P0734 sets. DTC P0734 is a type D DTC.
Conditions for Running the DTC
| • | The system voltage is 8.0-18.0 volts. |
| • | The engine speed is greater than 475 RPM for greater than 7 seconds. |
| • | No OSS DTCs P0722 or P0723. |
| • | No ISS DTCs P0716 or P0717. |
| • | No TFP manual valve position switch DTC P1810. |
| • | No TFP manual valve position switch changes for greater than 7 seconds. |
| • | The vehicle speed is greater than 4 km/h (2.4 mph). |
| • | The TFT is 20-149°C (68-300°F). |
| • | The vehicle is not in PARK or NEUTRAL. |
| • | The APP angle is greater than 15%. |
| • | The engine torque is 150-675 N·m (110-500 lb ft). |
Conditions for Setting the DTC
| • | Fourth gear is commanded for greater than 7 seconds. |
| • | Gear ratio is 0.70-3.27. |
| • | The gear ratio is one of the following ranges: |
| - | Greater than 2.52 or less than 2.43 |
| - | Greater than 1.50 or less than 1.45 |
| - | Greater than 1.03 or less than 0.97 |
| - | Greater than 2.11 or less than 2.05 |
Action Taken When the DTC Sets
| • | The PCM does not illuminate the malfunction indicator lamp (MIL). |
| • | The PCM commands maximum line pressure. |
| • | The PCM freezes shift adapts. |
| • | The PCM stores DTC P0734 in PCM history. |
Conditions for Clearing the DTC
| • | A scan tool clears the DTC from PCM history. |
| • | The PCM clears the DTC from PCM history if the vehicle completes 40 consecutive warm-up cycles without a non-emission-related diagnostic fault occurring. |
| • | The PCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the PCM. |
Diagnostic Aids
| • | Sticking or contaminated shift valves may cause an undefined gear ratio. |
| • | Refer to the Shift Solenoid Valve State and Gear Ratio table. |
| • | First diagnose and clear any engine DTCs that are present. Then inspect for any transmission DTCs that may have reset. If DTC P0717 and DTC P0734 are both present, diagnose DTC P0717 first. |
| • | DTC P1870 detects an incorrect gear ratio in fourth gear with TCC applied. |
| • | A faulty 4WD front axle switch circuit may cause a DTC P0734 to set. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests the indicated range signal to the actual selected range. A faulty TFP manual valve position switch could set DTC P0734.
-
This step tests for proper ratios in each commanded gear state.
Step | Action | Value(s) | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||||||||
2 | Perform the Transmission Fluid Checking Procedure. Refer to Transmission Fluid Check . Is the procedure complete? | -- | Go to Transmission Fluid Check | |||||||||||||
Important: Before clearing the DTCs, use the scan tool in order to record the Failure Records. Using the Clear Info function erases the Failure Records from the PCM. Does the scan tool TFP Switch A/B/C display match each selected gear range? (Refer to the Range Signal table). | -- | |||||||||||||||
Are the gear ratios within the parameters for the specified gear range? | 4th-0.73-0.77 | Go to Diagnostic Aids | ||||||||||||||
5 |
Refer to Line Pressure Check . Is the line pressure within specifications for each selected gear range? | -- | ||||||||||||||
6 |
Refer to AT Fluid/Filter Changing. Was excessive contamination found? | -- | Go to Unit Repair | |||||||||||||
7 | Inspect the transmission for the following conditions:
Was the condition found? | -- | Go to Unit Repair | |||||||||||||
8 | Is the system line pressure low only in the specific gear which indicated an incorrect gear ratio? | -- | Go to Symptom Diagnosis Low Line Pressure | |||||||||||||
9 | Inspect for fluid pressure loss in the following areas:
Was the condition found? | -- | Go to Unit Repair | |||||||||||||
10 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK |
