GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Equinox 🢒 Brakes 🢒 Park Brake 🢒 DTC P0734

Circuit Description

The transmission control module (TCM) calculates gear ratio based on data from the automatic transmission input shaft speed (AT ISS) and automatic transmission output shaft speed (AT OSS) sensors. The TCM compares the calculated gear ratio to the known gear ratio for each commanded gear.

If the TCM detects an incorrect 4th gear ratio, indicating excessive slip or drag within the transmission, then DTC P0734 sets. DTC P0734 is a type A DTC.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0734 Incorrect 4th Gear Ratio

Conditions for Running the DTC
    • No TR switch DTC P0705.
    • No TFT DTCs P0711, P0712, or P0713.
    • No ISS DTC P0717.
    • No OSS DTC P0722.
    • No engine speed DTC P0727.
    • No TCC DTC P0741.
    • No solenoid DTCs P0962, P0963, P0966, P0967, P0970, P0971, P0973, P0974, P0976, P0977, P0979, P0980, P0982, P0983, P0985, or P0986.
    • No engine torque DTC P1781.
    • No throttle position DTC P1791.
    • No CAN DTCs U2104 or U2105.
    • The brake switch is released.
    • The ignition voltage is 10.5-18 volts.
    • The transmission temperature is greater than 20°C (68°F).
    • The transmission is in a forward range.
    • The elapsed time since the most recent range change is 8 seconds or greater.
    • The throttle position (TP) is 10 percent or greater.
    • The engine speed is at least 400 RPM.
    • The commanded gear has been 4th for 0.5 seconds or greater.
    • The transmission output shaft speed (OSS) is 500 RPM or greater.

Conditions for Setting the DTC

The TCM commands 4th gear and the actual gear ratio is not within 1.03:1-1.53:1 for 12 seconds.

Action Taken When the DTC Sets
    • The TCM requests the powertrain control module (PCM) to illuminate the malfunction indicator lamp (MIL).
    • The TCM turns the Trans. Protection Mode ON. When the Trans. Protection Mode is ON, the following conditions occur:
       - The transmission will operate in 5th gear when the transmission is shifted into D or I range and 2nd gear when shifted into L range.
       - The line pressure is at maximum.
       - The torque converter clutch (TCC) is disabled.
       - The TCM freezes the transmission adaptive functions.
    • The TCM requests the PCM to limit engine torque to 150 N·m (111 lb ft).
    • The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as a Failure Record.
    • The TCM stores DTC P0734 in TCM history.

Conditions for Clearing the MIL/DTC
    • The PCM turns off the MIL after the third consecutive drive trip in which the TCM does not send a MIL illumination request.
    • A scan tool can clear the DTC.
    • The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
    • The TCM cancels the DTC default actions when the ignition is OFF long enough in order to power down the TCM.

Diagnostic Aids

Ask the customer about overloading the vehicle, exceeding the trailer towing limit, or towing in DRIVE (D).

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step determines that shift solenoid 2 or the M2 shift valve is stuck if the 4th gear ratio is 0.98:1.

    2.

  2. This step determines if the output shaft speed sensor signal is skewed by a large factor.

    3.

  3. This step determines if the input shaft speed sensor signal is skewed by a large factor.

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle in Vehicle DTC Information?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Inspect for correct transmission fluid level. Refer to Transmission Fluid Check .

Is the transmission fluid level correct?

--

Go to Step 4

Go to Step 3

3
  1. Visually inspect the transmission cooling system for fluid leaks. Refer to Fluid Leak Diagnosis .
  2. Repair leaks as necessary.
  3. Fill the transmission to the proper fluid level.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 4

4
  1. Install a scan tool.
  2. Turn the ignition ON, with the engine OFF.

    3. Important: 

       • Before clearing the DTC, use the scan tool in order to record the PCM and the TCM Failure Records. Using the Clear Eng./Trans. DTC Info function erases the Failure Records from the PCM and TCM.
       • Using the Clear Eng./Trans. DTC Info function erases stored DTCs in both the PCM and TCM.

  3. Record the DTC Failure Records.
  4. Clear the DTC.
  5. Use the scan tool snapshot mode in order to record commanded gear and gear ratio.
  6. Drive the vehicle in DRIVE (D) and record the gear ratio while accelerating in 4th gear.

Is the 4th gear ratio within the specified range?

1.03:1-1.53:1

Go to Intermittent Conditions in Engine Controls - 3.4L

Go to Step 5

5

Is the 4th gear ratio equal to the specified value?

0.98:1

Go to Step 12

Go to Step 6

6

  1. Drive the vehicle.
  2. Observe Transmission OSS parameter with a scan tool.
  3. Compare with a known good vehicle.

Is Transmission OSS parameter reading correctly?

--

Go to Step 7

Go to Step 17

7

  1. Stop the vehicle and apply the parking brake.
  2. Place the gear selector in PARK (P).
  3. Allow the engine to idle.
  4. Observe Transmission AT ISS parameter with a scan tool.

Is Transmission AT ISS parameter within the specified range?

400-800 RPM

Go to Step 8

Go to Step 16

8
  1. Turn the ignition ON, with the engine OFF.
  2. Command shift solenoid 1 ON and OFF with a scan tool.

Does shift solenoid 1 click when commanded ON?

--

Go to Step 9

Go to Step 18

9

Command shift solenoid 3 ON and OFF with a scan tool.

Does shift solenoid 3 click when commanded ON and OFF?

--

Go to Step 10

Go to Step 19

10

Perform a line pressure test. Refer to Line Pressure Check .

Is the action complete?

--

Go to Step 11

--

11
  1. Remove the control valve body cover (29). Refer to Control Valve Body Cover Removal in Unit Repair.
  2. Inspect the inside of the control valve body cover (29) for excessive sediment.

Did you find excessive amounts of sediment?

--

Go to Step 15

Go to Step 13

12

Inspect the control valve body assembly (39) for the following conditions:

    • Stuck 2-3, 3-4 shift solenoid valve assembly (S2) - light gray (308)
    • Stuck M2 shift valve (426)

Refer to Control Valve Body Assembly Disassemble in Unit Repair.

Did you find any of the above conditions?

--

Go to Step 20

Go to Step 14

13

Inspect the control valve body assembly (39) for the following conditions:

    • Stuck M1 shift valve (389)
    • Stuck U1 shift valve (386)
    • Stuck U2 shift valve (392)
    • Stuck shift pressure relay valve (424)
    • Stuck neutral relay valve (356)
    • Stuck line pressure control solenoid valve assembly (SLT) (316)

Refer to Control Valve Rear Body Disassemble and Control Valve Body Disassemble - Middle in Unit Repair.

Did you find any of the above conditions?

--

Go to Step 20

Go to Step 14

14

Has the control valve body been serviced within the past 3 months or 4,828 km (3,000 mi)?

--

Go to Step 15

Go to Step 20

15

Inspect the following items:

    • 4-5 clutch (C3) (577)
    • Forward clutch (C1) (552)

Refer to 4-5 Clutch Drum Assembly Assemble and Forward and Direct Clutch Assembly Assemble in Unit Repair.

Is the action complete?

--

Go to Step 21

--

16

Replace the input shaft speed sensor (73). Refer to Input Speed Sensor Replacement .

Is the replacement complete?

--

Go to Step 23

--

17

Replace the output shaft speed sensor (62). Refer to Output Speed Sensor Replacement .

Is the replacement complete?

--

Go to Step 23

--

18

Replace the reverse, 1st shift solenoid valve assembly (S1) - black (310). Refer to Control Valve Body Assembly Disassemble in Unit Repair.

Is the replacement complete?

--

Go to Step 23

--

19

Replace the 1-2, 2-3, reverse shift solenoid valve assembly (S3) - dark gray (300). Refer to Control Valve Body Assembly Disassemble in Unit Repair.

Is the replacement complete?

--

Go to Step 23

--

20

Repair or replace the control valve body assembly (39). Refer to Control Valve Body Replacement .

Is the action complete?

--

Go to Step 22

--

21

Repair or replace the transmission. Refer to Transmission Replacement .

Is the action complete?

--

Go to Step 22

--

22
  1. Replace the transmission fluid. Refer to Transmission Fluid Replacement .
  2. Inspect for the correct level of transmission fluid.
  3. Add new fluid as necessary.

    4. Important: The Reset Trans Adapts function will clear all adapt cells. This may affect transmission performance. The TCM will update the adapt cell values as the vehicle is driven.

  4. Use the scan tool in order to perform the following:
    5. • Reset oil life monitor to 100 percent.
    • Reset Trans Adapts.

Did you complete the above procedures?

--

Go to Step 23

--

23

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle.
  4. Select Specific DTC.
  5. Enter DTC P0734.

Does the DTC reset?

--

Go to Step 2

Go to Step 24

24

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?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK