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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Cab/Chassis HD (GMT 400) 🢒 DTC 🢒 DTC P1811

DTC P1811 Diesel Only

Circuit Description

The powertrain control module (PCM) compares the measured gear ratio to the known value. This allows the PCM to determine the actual gear range of the transmission. When an upshift is commanded, the PCM measures the amount of time it takes to obtain the next gear ratio. This interval is expressed on the scan tool as Shift Time. When this interval has exceeded a predetermined limit, the PCM utilizes the shift adapts in order to attempt to shorten the shift time.

If the PCM detects that the maximum allowable shift time has been exceeded, and the upshift adapts have reached their upper limit, then DTC P1811 sets. DTC P1811 is a type C DTC.

Conditions for Running the DTC

The engine must be running for more than 7 seconds.

Conditions for Setting the DTC

One of the following conditions exists, with the adapt cells at the maximum pressure allowed for 5 consecutive occurrences of one shift.

    • The 1-2 or 2-3 upshifts are greater than 1.25 seconds.
    • The 3-4 upshift is greater than 6.37 seconds.

Action Taken When the DTC Sets
    • The PCM does not illuminate the malfunction indicator lamp (MIL).
    • The PCM freezes shift adapts.
    • The PCM commands maximum line pressure.
    • 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 P1811 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 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
    • DTC P1811 defaults to an elevated line pressure condition which may result in partial TCC apply. This may produce an idle surge that could stall the engine.
    • DTC P1811 can be caused by the turbocharger or wastegate assembly. If no other symptoms are present, check the turbocharger system for proper operation.
    • Ask the customer about overloading the vehicle, exceeding the trailer-towing limit, or towing in OVERDRIVE.
    • If, after several unsuccessful attempts to gain accurate shift times, and an adapt can be made, reset adapts and operate the vehicle, in order to assure proper shifting.
    • While driving the vehicle, inspect for loss of power, misfire, or other engine-related driving conditions.
    • Refer to Range Reference .

Test Description

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

  1. This step tests for low fluid level, which can cause delayed shifts.

    2.

  2. This step compares the indicated range signal from the Transmission Fluid Pressure (TFP) Manual Valve Position Switch Logic table to the automatic transmission fluid pressure (TFP) manual valve position switch selected gear range.

    3.

  3. This step tests for low line pressure, which can cause delayed and long shifts.

DTC P1811

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls in Engine Controls - 6.5L

2

Perform the Transmission Fluid Checking Procedure.

Refer to Transmission Fluid Check .

Did you perform the Transmission Fluid Checking Procedure?

--

Go to Step 3

Go to Transmission Fluid Check

3

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

    3. Important: Before clearing the DTC, use the scan tool in order to record the Failure Records. Using the Clear Info function erases the Failure Records from the PCM.

  3. Record the DTC Failure Records.
  4. Clear the DTC.

    5. Important: If any other engine or transmission DTCs are set, refer to their respective diagnostic tables first.

  5. Select TFP Sw. A/B/C on the scan tool.
  6. Start the engine and apply the brake pedal.
  7. Select each gear range: D1, D2, D3, D4, N, R, and P.

    8. Refer to Transmission Fluid Pressure Manual Valve Position Switch Logic .

Does each selected transmission range match the TFP Sw. A/B/C display on the scan tool?

--

Go to Step 4

Go to DTC P1810

4
  1. Drive the vehicle in D4 in order to obtain a 1-2, a 2-3, and a 3-4 shift time. Use the scan tool snapshot mode in order to record the shift times.
  2. Using the scan tool, review the shift time information for 1-2, 2-3, and 3-4 shifts.

Were all of the shift times greater than the specified value?

1-2 or 2-3 upshifts: 1.25 seconds

3-4 upshift: 6.37 seconds

Go to Step 5

Go to Step 8

5

Perform the Line Pressure Check Procedure.

Refer to Line Pressure Check .

Is the line pressure within specifications?

--

Go to Step 6

Go to Symptoms - Automatic Transmission

6
  1. Remove the transmission oil pan.

    2. Refer to Automatic Transmission Fluid and Filter Replacement .

  2. Inspect the pan and the fluid for contamination.

Is there excessive contamination in the transmission oil pan?

--

Go to Transmission Overhaul in Transmission Unit Repair Manual

Go to Step 7

7

Inspect the transmission for fluid pressure loss in one of the following areas:

    • The valve body gasket
    • The forward clutch seals
    • The turbine shaft seals

Refer to Transmission Overhaul in Transmission Unit Repair Manual.

Did you find and correct the condition?

--

Go to Step 15

--

8

Select the 1-2, 2-3, and the 3-4 Transmission Adaptive Pressure (TAP) cells on the scan tool.

Were any of the upshift TAP cells greater than the specified value?

110 kPa (16.0 psi)

Go to Step 9

Go to Diagnostic Aids

9

Did the 3-4 shift time exceed the specified value?

6.37 seconds

Go to Step 12

Go to Step 10

10

Did the 2-3 shift time exceed the specified value?

1.25 seconds

Go to Step 13

Go to Step 11

11

Did the 1-2 shift time exceed the specified value?

1.25 seconds

Go to Step 14

--

12

Inspect the following 3-4 shift circuit components:

    • The 4th gear clutch plates
    • The 4th gear clutch seals
    • A sticking 3-4 shift valve

Refer to Transmission Overhaul in Transmission Unit Repair Manual.

Did you find and correct the condition?

--

Go to Step 15

--

13

Inspect the following 2-3 shift circuit components:

    • The turbine shaft seals
    • The forward clutch plates
    • The forward clutch seals
    • The direct clutch plates
    • The direct clutch seals
    • The center support seals
    • An improperly tightened center support bolt

Refer to Transmission Overhaul in Transmission Unit Repair Manual.

Did you find and correct the condition?

--

Go to Step 15

--

14

Inspect the following 1-2 shift circuit components:

    • The low roller clutch
    • The intermediate clutch plates
    • The intermediate clutch seals
    • The intermediate sprag clutch
    • The overdrive roller clutch
    • An improperly tightened center support bolt

Refer to Transmission Overhaul in Transmission Unit Repair Manual.

Did you find and correct the condition?

--

Go to Step 15

--

15
  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 16

--

16

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Drive the vehicle in D4 range.
  4. Operate the vehicle through several 1-2 and 3-4 upshifts.
  5. Review the scan tool 1-2, 2-3 and 3-4 shift times.

Are the 1-2, 2-3, or 3-4 shift times less than the specified value?

1-2 and 2-3 upshifts: 1.25 seconds

3-4 upshift: 6.37 seconds

System OK

Go to Step 1