GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2008 🢒 Equinox 🢒 Power and Signal Distribution 🢒 Wiring Systems and Power Management 🢒 DTC P0734

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0734: Incorrect 4th Gear Ratio

Circuit/System Description

The transmission control module (TCM) calculates the actual gear ratio based on input speed sensor (ISS) and output speed sensor (OSS) data. The actual gear ratio is compared to the expected gear ratio for each commanded gear.

If the TCM detects an incorrect 4th gear ratio while in 4th gear, DTC P0734 sets.

Conditions for Running the DTC
    • No Throttle Position (TP) Sensor DTC P0120.
    • No Transmission Range (TR) Switch DTCs P0706, P0707, or P0708.
    • No Transmission Fluid Temperature (TFT) Sensor DTCs P0711, P0712, or P0713.
    • No Speed Sensor DTCs P0717, P0722, or P0727.
    • No Pressure Control (PC) Solenoid DTCs P0962, P0963, P0966, P0967, P0970, or P0971.
    • No Shift Solenoid (SS) Control Circuit DTCs P0973, P0974, P0976, P0977, P0979, P0980, P0982, P0983, P0985, or P0986.
    • No Transmission Torque Delivered Circuit DTC P2637.
    • No Communications DTCs U0100 or U2104.
    • Output speed greater than one half that of the input speed.
    • Input speed is greater than 400 RPM.
    • Current gear equals 4th.
    • Transmission fluid temperature (TFT) is greater than 20°C (68°F).
    • Engine speed is greater than 400 RPM.
    • Throttle position greater than 10 percent.
    • Shift range equals D, M, or L for at least 2 seconds.
    • Ignition voltage is greater than 10.5 volts.

Conditions for Setting the DTC

The following condition is met for 1 second, 12 occurrences.

The current ratio and the expected ratio differ by more than 20 percent.

Action Taken When the DTC Sets
    • DTC P0734 is a Type A DTC.
    • 5th gear in D or M.
    • 2nd gear in L.
    • Limit engine torque to 150 N·m (111 lb ft).

Conditions for Clearing the DTC

DTC P0734 is a Type A DTC.

Diagnostic Aids

Improper transmission fluid level may cause DTC P0734 to set. Refer to the Transmission Fluid Check procedure.

Reference Information

Schematic Reference

Automatic Transmission Controls Schematics

Connector End View Reference

    •  Electrical Center Identification Views
    •  Component Connector End Views
    •  Splice Pack Connector End Views
    •  Inline Harness Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

    •  Diagnostic Trouble Code (DTC) Type Definitions
    •  Diagnostic Trouble Code (DTC) List/Type

Scan Tool Reference

Control Module References for scan information.

Circuit/System Verification
  1. Ignition ON, observe the DTC information with a scan tool.
  2. Record Freeze Frame and Failure Records.
  3. Clear DTCs.
  4. Operate the vehicle under the conditions observed in the Failure Records.
  5. Observe the DTC information with the scan tool. Verify that the DTC does not set.

Circuit/System Testing
  1. Operate the vehicle in D.
  2. Using the scan tool record the gear ratio while accelerating in 4th gear. The gear ratio should be within 1.04:1-1.56:1.
    3. ⇒If the 4th gear ratio is 1.00:1, inspect and repair the control valve body assembly for the following conditions. Refer to Control Valve Body Assembly Disassemble .
    • Stuck 2-3, 3-4 shift solenoid valve assembly
    • Stuck M2 shift valve
    • If the conditions test normal, replace the control valve body assembly, Refer to Control Valve Body Replacement procedure.
         ⇒If the 4th gear ratio is not within the specified range and is not 1.00:1, continue to step 3.
  3. Observe the scan tool Transmission OSS parameter while driving the vehicle. The reading should correspond to a known properly functioning OSS.
    4. ⇒If the OSS is malfunctioning, replace the Transmission Output Speed Sensor (OSS). refer to the Output Speed Sensor Replacement procedure.
  4. Stop the vehicle, apply the parking brake, engine at idle, select P (park) using the Shift Control.
  5. Observe the scan tool Transmission ISS parameter. The reading should be within 400-800 RPM.
    6. ⇒If the ISS parameter is not within the specified range, replace the Transmission Input Speed Sensor (ISS). Refer to the Input Speed Sensor Replacement procedure.
  6. Ignition ON, engine OFF, command shift solenoid 1 ON and OFF with a scan tool. The solenoid should click when commanded ON.
    7. ⇒If the solenoid does not click, replace the 1st shift solenoid valve assembly. Refer to Control Valve Body Assembly Disassemble .
  7. Command shift solenoid 3 ON and OFF with a scan tool. The solenoid should click when commanded ON.
    8. ⇒If the solenoid does not click, replace the 1-2, 2-3, reverse shift solenoid valve assembly. Refer to Control Valve Body Assembly Disassemble .
  8. Perform a line pressure test. Refer to Line Pressure Check procedure.
  9. Remove the control valve body cover. Refer to Control Valve Body Cover Removal procedure.
  10. Inspect the inside of the control valve body cover for excessive sediment. There should not be excessive sediment.
    11. ⇒If excessive sediment is found inspect and replace as necessary the 4-5 clutch and forward clutch. Refer to 4-5 Clutch Drum Assembly Assemble and Forward and Direct Clutch Assembly Assemble procedures.
  11. Inspect the control valve body assembly for the following conditions. Refer to Control Valve Rear Body Disassemble and Control Valve Body Disassemble - Middle . The conditions should not be found.
    12. • Stuck U1 shift valve
    • Stuck M1 shift valve
    • Stuck U2 shift valve
    • Stuck shift pressure relay valve
    • Stuck neutral relay valve
    • Stuck line pressure control solenoid valve assembly
         ⇒If any of the above conditions are found, replace the valve body assembly. Refer to Control Valve Body Replacement procedure.
  12. Verify that the control valve body has been serviced within the past 3 months.
    13. ⇒If the control valve body has not been serviced, replace the control valve body assembly. Refer to Control Valve Body Replacement .
  13. If all circuits and components test normal, replace the transmission.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.