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For 1990-2009 cars only
Makes 🢒 Buick 🢒 2000 🢒 Regal 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P0730 Incorrect Gear Ratio

Circuit Description

The PCM calculates the gear ratio based on data from the automatic transmission input shaft speed (AT ISS) sensor and the vehicle speed sensor (VSS). The PCM compares the known transmission gear ratio to a calculated ratio for each gear range selected. The VSS output is translated to RPM and mph by the PCM for various uses.

If the PCM detects an incorrect gear ratio because of excessive slip within the transmission, then DTC P0730 sets. DTC P0730 is atype C DTC.

Conditions for Running the DTC
    • No TP sensor DTC P0121, P0122 or P0123.
    • No VSS DTC P0502 or P0503.
    • No AT ISS sensor DTC P0716 or P0717.
    • No TFP manual valve position switch DTC P1810.
    • The engine speed is greater than 500 RPM for 5 seconds and not in fuel shut off.
    • The transmission is not in PARK or NEUTRAL.
    • The transmission fluid temperature is greater than 20°C (68°F).
    • The TP angle is greater than 14%.
    • The vehicle speed is greater than 7 km/h (5 mph).
    • The MAP is 0-105 kPa (0-15 psi).
    • The engine torque is 70-407 N·m (50-300 lb ft).
    • The time since the last gear range change is greater than 6 seconds.

Conditions for Setting the DTC

DTC P0730 sets when one of the following conditions occurs for 7 seconds:

    • The gear ratio is more than 2.97:1.
    • The gear ratio is 2.43:1 to 2.87:1.
    • The gear ratio is 1.62:1 to 2.33:1.
    • The gear ratio is 1.05:1 to 1.52:1.
    • The gear ratio is 0.75:1 to 0.95:1.

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 records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Failure Records.
    • The PCM stores DTC P0730 in PCM history.

Conditions for Clearing the DTC
    • A scan tool can clear the DTC.
    • 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
    • Ask the customer about possible overloading, exceeding the trailer towing limit, or towing in overdrive.
    • Inspect for an incorrect calibration.
    • Refer to Range Reference .
    • Ensure the wiring harness is not stretched too tightly or other components are pressing on the A/T inline 20-way connector body. Also inspect for proper clearance to any other components and wiring. Refer to Intermittent Conditions in Engine Controls - 3.1L or Intermittent Conditions in Engine Controls - 3.8L.

Test Description

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

  1. This step tests for low fluid level, which may cause slipping and result in an undefined gear ratio.

    2.

  2. This step verifies that the correct gear ratios occur for commanded gears.

    3.

  3. This step tests for low line pressure.

DTC P0730 Incorrect Gear Ratio

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain Diagnostic System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls

2

Visually inspect the transmission cooling system for fluid leaks.

Refer to Fluid Leak Diagnosis .

Did you find the condition?

--

Go to Step 7

Go to Step 3

3

Did you perform the transmission fluid checking procedure?

--

Go to Step 4

Go to Transmission Fluid Check

4

  1. Install a Scan Tool .
  2. Start the engine.

    3. Important: Before clearing the DTCs, use the Scan Tool in order to record the Failure Records for reference. Using the Clear Info function will erase the stored Failure Records from the PCM.

  3. Record the Failure Records.
  4. Clear the DTCs.
  5. Using the Scan Tool , select Current Gear and Gear Ratio.
  6. Drive the vehicle in transmission gear ranges 1, 2, 3, 4 and REVERSE with the TP angle greater than 14%.
  7. Record the gear ratio for each gear.

Was each gear ratio within the specified range?

Reverse: 2.33:1 to 2.43:1

1st: 2.87:1 to 2.97:1

2nd: 1.52:1 to 1.62:1

3rd: 0.95:1 to 1.05:1

4th: 0.65:1 to 0.75:1

Go to Diagnostic Aids

Go to Step 5

5

Perform the line pressure check.

Refer to the Line Pressure Check .

Did you find the condition?

--

Go to Symptom Diagnosis

Go to Step 6

6

Inspect for clutch slippage.

Refer to the Symptom Diagnosis tables.

Did you complete the repair?

--

Go to Step 8

--

7

Repair the transmission cooling system as necessary.

Refer to Fluid Leak Diagnosis .

Did you complete the repair?

--

Go to Step 8

--

8
  1. Change the AT fluid and filter.
  2. Inspect for correct transmission fluid level.

    3. Refer to Transmission Fluid Check .

  3. Add new AT fluid as necessary.

    4. Important: The Clear TAPS function will clear all adapt cells. This may affect transmission performance. The PCM will update the transmission adapt cell values as the vehicle is driven.

  4. Using the Scan Tool , perform the Clear TAPS function.

Did you complete the above procedure?

--

Go to Step 9

--

9

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Start the engine and let the engine run until the transmission fluid temperature is greater than 20°C (68°F).
  4. Drive the vehicle with the TP angle greater than 14% and the vehicle speed greater than 7 km/h (5 mph). Ensure that any one of the gear ratio values are obtained for at least 7 seconds.
  5. Select Specific DTC.
  6. Enter DTC P0730.

Has the test run and passed?

Reverse: 2.33:1 to 2.43:1

1st: 2.87:1 to 2.97:1

2nd: 1.52:1 to 1.62:1

3rd: 0.95:1 to 1.05:1

4th: 0.65:1 to 0.75:1

System OK

Go to Step 1