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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2006 🢒 GMC Sierra Denali 🢒 Restraints 🢒 SIR 🢒 DTC P0826

Circuit Description

The transmission adaptive pressure (TAP) up/down shift system allows the driver to manually shift gears by using the TAP shift switch located on the automatic transmission shift lever. Pushing the switch forward will command an upshift and pushing the switch rearward will command a downshift. The TAP shift system is activated when the gear selector is in the manual (M) position.

DTC P0826 is a type B DTC.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0826 TAP Up and Down Shift Switch Circuit

Conditions for Running the DTC
    • The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
    • The engine, input, speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.
    • The output speed is greater than 200 RPM.
    • Driver shift request is commanded.

Conditions for Setting the DTC

DTC P0826 sets when the transmission control module (TCM) detects an open condition in the TAP up/down shift switch circuit for greater than 6 seconds when driver shift request is commanded.

Action Taken When the DTC Sets
    • The TCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
    • DTC P0826 is stored in TCM history.
    • The TCM disables driver shift request operations.

Conditions for Clearing the MIL/DTC

A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.

Diagnostic Aids
    • Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions:
       - A bent terminal
       - A backed-out terminal
       - A damaged terminal
       - Poor terminal tension
       - A chafed wire
       - A broken wire inside the insulation
    • When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
    • You may have to drive the vehicle in order to experience a condition.

Test Description

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

  1. This step tests signal voltage to the TCM.

    2.

  2. This step tests supply voltage to the driver shift request switch.

    3.

  3. This step tests resistance of the driver shift request switch.

Step

Action

Value

Yes

No

Schematic Reference: Automatic Transmission Controls Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Install the 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 Freeze Frame and Failure Records for reference. The Clear Info function will erase the data.

  3. Record the DTC Freeze Frame and Failure Records.
  4. Clear the DTC.
  5. Using the scan tool, measure ignition voltage.

Is the voltage within the specified range?

9-18 V

Go to Step 3

Go to DTC P0562 for low voltage or DTC P0563 for high voltage

3

  1. Turn the ignition OFF.
  2. Disconnect the 80-way connector at the TCM.
  3. Install the J 39700 breakout box, the J-47275 breakout box adapter and the J 47275-1 magnetic overlay.
  4. Turn ON the ignition, with the engine OFF.
  5. Using the DMM, measure voltage at terminal 56 and a known good ground.
  6. Operate the driver shift request switch in the TAP up and TAP down position.

Is the voltage within the specified value?

2.5 V

Go to Diagnostic Aids

Go to Step 4

4

  1. Turn the ignition OFF.
  2. Disconnect terminals 20 and 21 at the driver shift request switch.
  3. Using the J 35616 GM terminal test kit, connect the DMM to terminal 21 and a known good ground.
  4. Turn ON the ignition, with the engine OFF.

Is the voltage within the specified range?

11.75-12.75 V

Go to Step 5

Go to Step 6

5

  1. Turn the ignition OFF.
  2. Using the J 35616 , connect the DMM to terminals 20 and 21 of the driver shift request switch.
  3. Operate the driver shift request switch in the Tap up and Tap down position.

Is the resistance within the specified value?

OFF: 6.84 K ohms

Tap up: 1.87 K ohms

Tap down: 3.97 K ohms

Go to Step 7

Go to Step 9

6

Important: The condition that affects this circuit may exist in other connecting branches of the circuit. Refer to Power Distribution Schematics for complete circuit distribution.

  1. Inspect the ignition 0 voltage circuit for an open. Refer to Circuit Protection - Fuses .
  2. Replace the fuse if necessary.

Was the fuse open?

--

Go to Step 11

Go to Step 8

7

Test the signal circuit of the AT driver shift request switch for an open between the AT driver shift request switch and the TCM. Refer to Testing for Continuity and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 11

Go to Step 10

8

Test the ignition 0 voltage circuit of the AT driver shift request switch for an open between the fuse block and the AT driver shift request switch. Refer to Testing for Continuity and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 11

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9

Replace the AT driver shift request switch. Refer to Shift Lever Replacement .

Did you complete the replacement?

--

Go to Step 11

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10

Important: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.

Replace the TCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 11

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11

Perform the following procedure in order to verify the repair:

  1. Clear the DTC.
  2. Operate the vehicle while using the driver shift request switch.
  3. Select Specific DTC.
  4. Enter DTC P0826.

Has the test run and passed?

--

Go to Step 12

Go to Step 2

12

With the scan tool, observe the stored information, capture info and DTC info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK