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
DTC P1876: Up and Down Shift Enable Switch Circuit Low Voltage

### Diagnostic Fault Information

#### Driver Shift Request

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Normal Range = None
Tap Up/Tap Down Switch Signal Circuit | 0 V | 0 V | 5-12 V | --

### Circuit/System Description

The TAP Shift/driver shift control (DSC) allows the driver to shift gears by using the TAP switches located on the automatic transmission shifter. Pushing forward on the shifter will command an upshift and pulling back will command a downshift. Ignition voltage flows from the ignition 3 fuse through the TAP Switch resistor array to the Transmission Control Module (TCM). The TAP system is activated when the gear shift lever is in the D position and moved over into the DSC gate area. When the shifter is moved over into the DSC gate area, the TAP enable switch is closed and completes the TAP enable circuit from the Body Control Module (BCM) to ground.

### Conditions for Running the DTC

#### P0815 or P0816

• | Start the ignition voltage, run the engine.

• | IMS DTC is not set.

• | DTC P0826 is not set.

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

#### P0826

• | Active the ignition voltage.

• | The engine speed is between 500 and 6,500 RPM for at least 5 seconds.

#### P1876

• | Active the ignition voltage.

• | The engine speed is between 500 and 6,500 RPM for at least 5 seconds.

• | DTCs U0100, P0815, P0816, P0826, P1825 or P1915 are not set.

### Conditions for Setting the DTC

#### P0815

The TCM detects an upshift request for 3 seconds or 600 seconds in PARK, REVERSE, NEUTRAL, or D.

#### P0816

The TCM detects a downshift request for 3 seconds or 600 seconds in PARK, REVERSE, NEUTRAL, or D.

#### P0826

The TCM detects an invalid voltage on the TAP Up/ Down Signal Circuit for 8 seconds.

#### P1876

The TCM detects a TAP Enable Switch request 3 times when not in D6 range for 2 seconds.

### Action Taken When the DTC Sets

• | DTCs P0815, P0816, P0826, and P1876 are Type C DTCs.

• | The TCM disables TAP shift functions.

### Conditions for Clearing the DTC

DTCs P0815, P0816, P0826, and P1876 are Type C DTCs.

### Reference Information

#### Schematic Reference

Automatic Transmission Controls Schematics

#### Connector End View Reference

• | Automatic Transmission Inline 16-Way Connector End View

• | Automatic Transmission Internal Connector End Views

• | Automatic Transmission Related Connector End Views

#### DTC Type Reference

• | Diagnostic Trouble Code (DTC) Type Definitions

• | Diagnostic Trouble Code (DTC) List/Type

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

### Circuit/System Verification

#### P0815, P0816, or P0826

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.

⇒ | If the parameter does not change to reflect the selected position, proceed to Circuit/ System Testing.

#### P1876

With the engine ON, move the transmission range selector from the Park (P) range to the Drive (D6) range and over into the DSC gate while observing the Tap Up/Down Enable parameter on the scan tool in Body and Accessories/Instrument Panel scan tool data list. The parameter should display Enabled when in the DSC gate area, and Disabled in all other ranges.

⇒ | If the parameter does not change when the transmission range selector is in the DSC gate, proceed to Circuit/System Testing.

### Circuit/System Testing

#### P0815

1. Select the Driver Shift Request parameter.
2. Disconnect the Automatic Transmission (AT) shift program switch connector.

⇒ | If the parameter status changes from Upshift to Invalid, replace the AT shift program 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 Automatic Transmission (AT) shift program switch connector.

⇒ | If the parameter status changes from Downshift to Invalid, replace the AT shift program 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 3 voltage circuit for an open.

⇒ | If the fuse is Open, test the ignition 3 and the Tap/Up and Tap/down circuit for a short to ground.

⇒ | If the fuse is OK, test the ignition 3 and the Tap/Up and Tap/down signal circuit for an Open or Short to Voltage.

2. Test the AT/DSC shift program 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 control solenoid (w/body and TCM) valve assembly.

#### P1876

Key On, engine Off, in PARK, disconnect the Tap Up/Tap Down Enable Switch connector from the switch. Using a scan tool, observe the Tap Up/Down Enable parameter in Body and Accessories/Instrument Panel scan tool data list. The parameter should display Disabled.

⇒ | If the parameter does not display Disabled while disconnected, test the Tap Up/Tap Down Enable signal circuit for a short to ground. If no short to ground is found, replace the BCM.

⇒ | If the parameter displays Disabled when disconnected and Enabled when connected, ensure the mechanical enable switch linkage is not bent, binding, or damaged and if no concerns are found, replace the Tap Up/Tap Down Enable switch.

⇒ | If the parameter displays Disabled at all times, test the Tap Up/Tap Down ground circuit for an open or short to voltage.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Transmission Control Replacement

• | Control Module References for TCM replacement, setup, and programming