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 Descriptors

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 Up/Tap Down Switch Signal Circuit | 0 V | 0 V | 5-12 V | --

### Circuit/System Description

The transmission adaptive pressure (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. Ignition voltage flows from the ignition 1 fuse through the TAP switch resistor array to the transmission control module (TCM). The TAP shift system is activated when the gear selector is in the manual (M) position. In the M range 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. TAP system is deactivated in all other range positions.

### Conditions for Running the DTC

#### P0815 or P0816

• | No DTC P0826.

• | No DTCs P1825 or P1915.

• | The engine speed is between 500-7,500 RPM for at least 5 seconds.

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

### Conditions for Setting the DTC

#### P0815

The TCM detects a stuck ON upshift switch for 3 seconds in PARK, REVERSE, NEUTRAL, or D6- and for 600 seconds in PARK, REVERSE, NEUTRAL, D2, D4, OR D6.

#### P0816

The TCM detects a stuck ON downshift switch request for 3 seconds in PARK, REVERSE, NEUTRAL, or D6- and for 600 seconds in PARK, REVERSE, NEUTRAL, D2, D4, or D6.

#### P0826

The TCM detects an invalid voltage on the TAP up/down signal circuit for 8 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

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

### Circuit/System Verification

With the engine ON, engage the Tap Up and Tap Down switch positions while observing the Driver Shift Request scan tool parameter. The parameter should change to reflect the selected Up or Downshift switch position and with no Up or Downshift switch position selected the parameter should display None.

### Circuit/System Testing

#### P0815

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

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

⇒ | If the parameter status does not change, replace the control solenoid (w/body and TCM) valve assembly.

#### P0816

1. Select the Driver Shift Request parameter.
2. Disconnect the AT TAP shift switch connector.

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

⇒ | If the parameter status does not change, replace the control solenoid (w/body and TCM) valve assembly.

#### P0826

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

⇒ | If the fuse is open, test the ignition 1 and the tap up and tap down circuit for a short to ground.

⇒ | If the fuse is OK, test the ignition 1 and the tap up and tap down signal circuit for an open or short to voltage.

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

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

⇒ | If the resistance is within specifications, replace the control solenoid (w/body and TCM) valve assembly.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Replace the AT TAP shift switch - refer to Automatic Transmission Manual Shift Auxiliary Position Switch Replacement. .

• | Replace the control solenoid (w/body and TCM) valve assembly - refer to Control Module References for replacement, setup, and programming.