GM Service Manual Online
For 1990-2009 cars only

DTC P0731 Incorrect 1st Gear Ratio Diesel Only

Table 1: 4L80-E Range Reference, modified for DTCs P1870 & P1871
Table 2: DTC P0731 (Diesel)

4L80-E Range Reference, modified for DTCs P1870 & P1871

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

--

  • A = Applied
  • H = Holding
  • * = Holding but not effective
  • O = Overrunning

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 P0731 sets. DTC P0731 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

    • First gear is commanded for greater than 5 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 P0731 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 a DTC P0731 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 P0731 to set.

Test Description

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

  1. This step tests the indicated range signal to the actual selected range. A faulty TFP manual valve position switch could set DTC P0731.

  2. This step tests for proper ratios in each commanded gear state.

DTC P0731 (Diesel)

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Perform the Transmission Fluid Checking Procedure.

Refer to Transmission Fluid Check .

Is the procedure complete?

--

Go to Step 3

Go to Transmission Fluid Check

3

  1. Install the scan tool.
  2. With the engine OFF, turn the ignition switch to the RUN position.
  3. 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.

  4. Record the Freeze Frame and Failure Records.
  5. Clear the DTCs.
  6. Start the engine.
  7. Apply the parking brake, and select each transmission range: D1, D2, D3, D4, N, R, and P.

Does the scan tool TFP Switch A/B/C display match each selected gear range? (Refer to the Range Signal table).

--

Go to Step 4

Go to DTC P1810 TFP Valve Position Switch Invalid Range

4

  1. Drive the vehicle in D1.
  2. Hold the vehicle in 1st gear for greater than 2 seconds.
  3. Use the scan tool snapshot mode in order to record the transmission 1st gear ratio.

Are the gear ratios within the parameters for the specified gear range?

1st-2.52-2.42

Go to Diagnostic Aids

Go to Step 5

5

  1. Connect the J 21867 pressure gauge to the transmission line pressure tap.
  2. Perform the Line Pressure Check Procedure.
  3. Refer to Line Pressure Check .

Is the line pressure within specifications for the selected gear range?

--

Go to Step 6

Go to Step 8

6

  1. Remove the transmission oil pan.
  2. Refer to AT Fluid/Filter Changing.

  3. Inspect the oil pan and the fluid for contamination.

Was excessive contamination found?

--

Go to Unit Repair

Go to Step 7

7

Inspect the transmission for the following conditions:

    • Sticking shift valves
    • Stuck apply pistons

Was the condition found?

--

Go to Step 10

Go to Unit Repair

8

Is the system line pressure low only in the specific gear which indicated an incorrect gear ratio?

--

Go to Step 9

Go to Symptom Diagnosis Low Line Pressure

9

Inspect for fluid pressure loss in the following areas:

    • 1-2 SS valve seal
    • 2-3 SS valve seal
    • Valve body passages
    • Valve body gaskets
    • Band apply pistons and seals
    • Clutch apply pistons and seals.

Was the condition found?

--

Go to Step 10

Go to Unit Repair

10

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle under the following conditions:
  4. • Start the engine.
    • Drive the vehicle in 1st gear.
    • The PCM must see a valid gear ratio versus the commanded gear ratio for 7 seconds.
  5. Select Specific DTC.
  6. Enter DTC P0731.

Has the test run and passed?

--

System OK

Go to Step 1