For 1990-2009 cars

### Circuit Description

The TAP Shift system allows the driver to manually shift gears by using the TAP Shift switches located on the automatic transmission shifter. Pushing the Up switch will command an upshift and pushing the Down switch will command a downshift. The TAP Shift system is activated when the gear selector is in the manual, M, position and is deactivated in all other positions.

If the transmission control module (TCM) detects an invalid voltage on the Up/Down Switch Circuit, DTC P0826 sets. DTC P0826 is a type C DTC.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0826 Up and Down Shift Switch Circuit

### Conditions for Running the DTC

• | Ignition voltage is between 8-18 volts.

• | The engine speed is between 450-6,800 RPM, for 5 seconds.

### Conditions for Setting the DTC

The TCM detects an invalid voltage on the TAP Up/Down Signal Circuit for 300 seconds (5 minutes).

### Action Taken When the DTC Sets

• | The TCM does not request the engine control module to illuminate the malfunction indicator lamp (MIL).

• | The TCM disables TAP Shift operation.

• | The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as a Failure Record.

• | The TCM stores DTC P0826 in TCM history.

### Conditions for Clearing the DTC

• | A scan tool can clear the DTC.

• | The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without a non-emission related diagnostic fault occurring.

• | The TCM cancels the DTC default actions when the fault no longer exists and the DTC passes.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

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

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

3. Record the DTC Failure Records.
4. Clear the DTC.
5. Select Driver Shift Request Status on the scan tool.

Does the scan tool Driver Shift Request parameter display None?

--

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3 |

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

Was the fuse open?

--

Go to Step 4

Go to Step 5

4 |

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. Test the ignition 1 voltage circuit of the floor shift control switch for a short to ground between the fuse block and the floor shift control switch.
2. Test the signal circuit for a short to ground between the floor shift control switch and the TCM.

Refer to Testing for Short to Ground and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 10

Go to Testing for Intermittent Conditions and Poor Connections

5 | Test the ignition 1 voltage circuit of the floor shift control switch for an open to ground between the fuse block and the floor shift control switch. Refer to Testing for Continuity and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 6
6 | Test the signal circuit of the floor shift control switch for an open, short to voltage or short to ground between the floor shift control switch and the TCM. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 7
7 |

1. Using the J 35616 GM terminal test kit, connect a DMM between the ignition 1 voltage circuit and the TAP Up/TAP Down signal circuit of the floor shift control.
2. Measure the resistance.

Is the resistance near the specified range?

8.11-8.39K Ω

Go to Step 9

Go to Step 8

8 | Replace the Floor Shift Control System. Refer to Transmission Control Replacement . Did you complete the replacement? | -- | Go to Step 10 | --
9 | Replace the TCM. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | -- | Go to Step 10 | --
10 | Perform the following procedure in order to verify the repair:

1. Select DTC.
2. Select Clear DTC Information.
3. Operate the vehicle under the following conditions:

• | Start the engine.

• | Observe Driver Shift Request on the scan tool.

• | Ensure the Driver Shift Request is not invalid for at least 1 second.

4. Select Specific DTC.
5. Enter DTC P0826.

Has the test run and passed?

--

Go to Step 11

Go to Step 2

11 | With a 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