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

### Typical Scan Tool Data

#### Driver Shift Request

Circuit | Short to Ground | Open/High Resistance | Short to Voltage
--- | --- | --- | ---
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

• | The engine speed is greater than 500 RPM for at least 5 seconds.

• | The ignition voltage is between 9.0 volts and 19.0 volts.

• | No TAP system DTC P0826.

• | No IMS DTCs P1825 or P1915.

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

#### P0816

• | The engine speed is greater than 500 RPM for at least 5 seconds.

• | The ignition voltage is between 9.0 volts and 19.0 volts.

• | No TAP system DTC P0826.

• | No IMS DTCs P1825 or P1915.

• | The time since the last gear selector range change is greater than 5 seconds.

#### P0826

• | The engine speed is greater than 500 RPM for at least 5 seconds.

• | The ignition voltage is between 9.0 volts and 19.0 volts.

#### P1876

• | The engine speed is greater than 500 RPM for at least 5 seconds.

• | The ignition voltage is between 9.0 volts and 19.0 volts.

• | No TAP system DTCs P0815, P0816, or P0826.

• | No IMS DTCs P1825 or P1915.

• | No ECM Communication Code U0100.

• | The time since the last gear selector range change is greater than 5 seconds.

### Conditions for Setting the DTC

#### P0815 - Condition 1

The TCM detects an upshift request for 3 seconds or greater in PARK, REVERSE, NEUTRAL, or D6.

#### P0815 - Condition 2

The TCM detects an upshift for 600 seconds in PARK, REVERSE, NEUTRAL, D2, D4, OR D6.

#### P0816 - Condition 1

The TCM detects a downshift request for 3 seconds in PARK, REVERSE, NEUTRAL, or D6.

#### P0816 - Condition 2

The TCM detects a downshift request 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 or greater.

#### P1876

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

### Action Taken When the DTC Sets

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

• | The TCM disables TAP shift operation.

### Conditions for Clearing the DTC

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

### Diagnostic Aids

• | DTC P0815 detects when the up-switch circuit is continuously sending an ON signal.

• | DTC P0846 detects when the down-switch circuit is continuously sending an OFF signal.

• | DTC P0826 detects when the up-shift/down-shift switch circuit is sending an illegal voltage.

• | DTC P1876 detects a continuous up-shift/down-shift request when not in D6.

### Reference Information

#### Schematic Reference

Automatic Transmission Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

• | Transmission General Description

• | Transmission Component and System 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

Control Module References for scan tool information

### Circuit/System Verification

#### P0815, P0816, and P0826

1. 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. When no Upshift or Downshift command is made, the parameter should display NONE.
2. 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.

#### P1876

1. With the engine ON, move the transmission range selector form the Park (P) range to the manual (M) position range 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 manual (M) position range, and DISABLED in all other ranges.

⇒ | If the parameter does not change when the transmission range selector is in manual (M) position range, proceed to Circuit/System Testing.

2. 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

#### 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 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 control solenoid (w/body and TCM) valve assembly.

#### P1876

Key On, engine Off, transmission range selector 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.

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

• | Refer to Transmission Control Replacement for AT TAP shift switch replacement.