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 P1876: Up and Down Shift Switch Performance - Range Switch Not in D3

### 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

• | The following DTCs are not Fault Active or Test Fail this Key ON:

- | DTC U0100.

- | DTCs P0815, P0816, or P0826.

- | DTCs P1825 or P1915.

• | Ignition voltage is 8.6-19.0 V.

• | Engine speed is 500-6,500 RPM for at least 5 seconds.

### Conditions for Setting the DTC

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

### Action Taken When the DTC Sets

• | DTC P1876 is a Type C DTC.

• | The TCM disables TAP shift functions.

### Conditions for Clearing the DTC

DTC P1876 is a Type C DTC.

### 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

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

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

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.

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

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