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 Enable Switch Circuit Low Voltage

### 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.

### Conditions for Running the DTC

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

• | No IMS range DTCs P1820, P1822, P1823, P1825, P1826 or P1915.

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

• | No CAN errors present.

### Conditions for Setting the DTC

The TCM detects the TAP enable switch is Active and the IMS range is not D for 5 seconds.

### Action Taken When the DTC Sets

The TCM disables TAP Shift operation.

### 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

#### 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 Testing

1. Check to see if any IMS DTCs are set.

⇒ | If any IMS DTCs are set, diagnose them first.

2. Turn ON the ignition leaving the engine OFF. Disconnect the automatic transmission control assembly connector. Using a DMM test the voltage on the Tap Up/Tap Down enable switch circuit at the automatic transmission control assembly connector. The voltage should be near battery voltage.

⇒ | If the voltage is not near battery voltage, test the Tap Up/Tap Down enable switch circuit for an open.

3. While observing the Driver Shift Control parameter on the scan tool place the shifter in D4. The Driver Shift Control parameter should display Active.

⇒ | If the Driver Shift Control parameter does not indicate Active, test the ground circuit at the automatic transmission control assembly for an open circuit.

4. If the Tap Up/Tap Down enable signal or the ground circuit is not open, test the Tap Up/Tap Down enable signal circuit for a short to ground.

⇒ | If any of the conditions are not found, test the automatic transmission control assembly.

### Component Testing

Disconnect the automatic transmission control assembly connector. Place the automatic transmission control assembly in D. Measure the resistance between the Tap Up/Tap Down enable signal circuit and the ground circuit of the automatic transmission control assembly. The resistance should be less than 1 ohm.

⇒ | If the resistance is greater than 1 ohm, replace the automatic transmission control assembly.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Manual Shift Shaft Position Switch Replacement

• | Transmission Internal Electrical Harness Replacement

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