For 1990-2009 cars

### 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 P0730: Incorrect 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 1st gear ratio while decelerating in 1st gear, DTC P0730 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, P0727

• | No Torque Converter Clutch (TCC) System - Stuck Off DTC P0741

• | 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

• | Output speed is 500-1260 RPM

• | Throttle position equals 0 percent

• | Range equals L for 8 seconds

• | The transmission fluid temperature (TFT) is greater than 20°C

• | The engine speed is greater than 400 RPM

• | The ignition voltage is greater than 10.5 volts

### Conditions for Setting the DTC

• | The TCM commands 1st gear with engine braking.

• | The TCM detects that the actual gear ratio and the expected gear ratio differ by more than 20 percent.

• | The condition exists for more than 12 seconds.

### Action Taken When the DTC Sets

• | Type A DTC

• | The transmission will operate in 5th gear in D or M range, 2nd gear in L range.

• | The engine torque is limited to 150 N·m

### Conditions for Clearing the DTC

DTC P0730 is a Type A DTC

### Diagnostic Aids

Improper transmission fluid level may cause DTC P0730 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

• | Powertrain Diagnostic Trouble Code (DTC) Type Definitions

• | Diagnostic Trouble Code (DTC) List - Vehicle

#### 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 2nd gear. The engine should not stall when shifting into 2nd gear.

⇒ | Inspect and repair as necessary, the control valve body assembly for a stuck 3-4, 4-5 solenoid valve or a stuck U1 shift valve. Refer to the Control Valve Body Assembly Disassemble procedure.

2. Observe the scan tool Transmission OSS parameter. The reading should correspond to a known properly functioning OSS.

⇒ | If the OSS is malfunctioning, replace the Transmission Output Speed Sensor (OSS). Refer to the Output Speed Sensor Replacement procedure.

3. Stop the vehicle, apply the parking brake, engine at idle, select P (park) using the Shift Control.
4. Observe the scan tool Transmission ISS parameter. The reading should be within 400 N·m 800 RPM.

⇒ | If the ISS parameter is not within the specified range, replace the Transmission Input Speed Sensor (OSS). Refer to the Input Speed Sensor Replacement procedure.

5. Firmly apply the brake, select D (drive) using the Shift Control.
6. Observe the scan tool TCC Slip Speed. The reading should be within 0-100 RPM.

⇒ | If the TCC Slip Speed is not within the specified range

• | Ignition ON, engine OFF, command shift solenoid 1 ON and OFF with a scan tool. The solenoid should click when commanded ON.

⇒ | If the solenoid does not click, replace the 1st shift solenoid valve assembly. Refer to Control Valve Body Assembly Disassemble .

• | Command shift solenoid 5 ON and OFF with a scan tool. The solenoid should click when commanded ON.

⇒ | If the solenoid does not click, replace the reverse shift solenoid valve assembly. Refer to Control Valve Body Assembly Disassemble .

• | Perform a line pressure test. Refer to Line Pressure Check procedure.

• | Remove the Control valve body cover. Refer to Control Valve Body Cover Removal procedure.

• | Inspect the inside of the control valve body cover for excessive sediment. There should not be excessive sediment.

⇒ | If excessive sediment is found inspect and replace as necessary the Low clutch sprag, Forward clutch, and 1-2, reverse clutch. Refer to Front Internal Gear and Overrun Roller Clutch Assemble , Forward and Direct Clutch Assembly Assemble and 1-2-Reverse Clutch Plate Assemble procedures.

• | 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.

• | Stuck shift pressure relay valve

• | Stuck M1 shift valve

• | Line pressure control solenoid valve assembly stuck closed

⇒ | If any of the above conditions are found, replace the valve body assembly. Refer to Control Valve Body Replacement procedure.

• | Verify that the control valve body has been serviced within the past 3 months.

⇒ | If the control valve body has not been serviced, replace the control valve body assembly. Refer to Control Valve Body Replacement procedure.

⇒ | If all circuits and components test normal, replace the transmission.

7. If all circuits and components test normal, replace the transmission.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.