For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P0815: Upshift Switch Circuit
DTC P0816: Downshift Switch Circuit
DTC P0826: Up and Down Shift Switch Circuit

### Diagnostic Fault Information

Driver Shift Request Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Tap Upshift Switch | P0826 | P0826 | P0815 | --
Tap Downshift Switch | P0826 | P0826 | P0816 | --
Up and Down Shift Switch | P0826 | P0826 | P0826 | --

### Circuit/System Description

The TAP Shift system allows the driver to manually shift gears by using the Upshift and Downshift positions located on the automatic transmission shift Lever. Pushing the lever to the Upshift position will command an upshift and pushing the lever to the Downshift position 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. In the M position, the TAP enable switch is closed and this activates the system by completing the TAP enable signal circuit from the body control module (BCM) to ground.

### Conditions for Running the DTC

#### P0815

• | No Tap up/Tap down DTC P0826.

• | No IMS DTCs P182A, P182C, P182D, P182E, P182F or P1915.

• | The engine run time is greater than 5 seconds.

• | The time since last gear selector range change is greater than 6 seconds.

#### P0816

• | No Tap up/Tap down DTC P0826.

• | No IMS DTCs P182A, P182C, P182D, P182E, P182F or P1915.

• | The engine run time is greater than 5 seconds.

• | The time since last gear selector range change is greater than 6 seconds.

#### P0826

The engine run time is greater than 5 seconds.

### Conditions for Setting the DTC

#### P0815

The TCM detects an upshift request for 2 seconds in PARK or for 600 seconds.

#### P0816

The TCM detects a downshift request for 2 seconds in PARK or for 600 seconds.

#### P0826

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

### Action Taken When the DTC Sets

• | DTCs P0815, P0816 and P0826 are Type C DTCs.

• | The TCM disables TAP Shift operation.

### Conditions for Clearing the DTC

DTCs P0815, P0816 and P0826 are Type C DTCs.

### Reference Information

#### Schematic Reference

Automatic Transmission Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Transmission General Description

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Transmission Control Module Scan Tool Information

### Circuit/System Verification

1. Ignition ON, transmission shift lever in M, observe the scan tool Driver Shift Request parameter. The reading should display None.
2. Observe the scan tool Driver Shift Request parameter while pressing the tap-up and tap-down switch. The reading should change between Upshift and Downshift.
3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

1. Select the Driver Shift Request parameter.
2. Disconnect the automatic transmission (AT) TAP shift switch connector.

⇒ | If the parameter status changes from Upshift or Downshift to Invalid, replace the AT TAP shift switch.

⇒ | If the parameter status does not change, check ignition 1 voltage circuit, if no trouble found, replace TCM.

#### P0826

1. Inspect the fuse in the ignition 1 voltage circuit for an open.

⇒ | If the fuse is open, test the following circuits for a short to ground:

• | The ignition 1 circuit

• | The Tap Up circuit

• | The Tap Down circuit

⇒ | If the fuse is OK, test the following circuits for an open or short to voltage.

• | The ignition 1 circuit

• | The Tap Up circuit

• | The Tap Down circuit

2. Test the AT TAP shift switch for correct resistance value, 8.11-8.39 ohms.

⇒ | If the resistance is not within specifications, replace the switch assembly.

⇒ | If the resistance is within specifications, replace the TCM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• | Replace the AT shift switch. Refer to Transmission Control Replacement.

• | Refer to Control Module References for replacement, setup, and programming