6T70/6T75 - Automatic Transmission

DTC P1876

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions 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

When the shift lever is placed in manual mode (M), the driver shift request (DSR), also known as the tap shift function, is activated. The DSR allows the vehicle operator to shift gears by pressing the plus (+) button for an upshift or the minus (-) button for a downshift. The body control module (BCM) provides ignition voltage to the resistor array in the switch. When a plus or minus button is pressed, there is a corresponding change in the resistance, resulting in change to the voltage drop. The change in voltage on the signal circuit is monitored by the transmission control module (TCM). The TCM commands the upshift or downshift, providing the operating conditions are correct for the shift.

Conditions for Running the DTC

* No TAP system DTCs P0815, P0816, or P0826.
* No IMS DTCs P1825 or P1915.
* No Communication DTC U0100.
* The engine speed is greater than 500 RPM for 5 seconds.
* The ignition voltage is between 8.6 volts and 19.0 volts.

Conditions for Setting the DTC

The Tap Up/Tap Down switch signal is Active when the IMS does not indicate L (M) for 2 seconds or greater 3 times during the same ignition cycle.

Action Taken When the DTC Sets

* DTC P1876 is a Type C DTC.
* The TCM disables Tap shift functions.

Conditions for Clearing the DIC/DTC

DTC P1876 is a Type C DTC.

Reference Information
Schematic Reference

Automatic Transmission Controls Schematics Electrical Diagrams
Connector End View Reference

Component Connector End Views Connector End Views By Name
Description and Operation

* Transmission General Description Transmission General Description
* Electronic Component Description Electronic Component Description

Electrical Information Reference

* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference

Control Module References Control Module References for scan tool information

Circuit/System Verification

1. Verify there are no IMS DTCs set.

• If IMS DTCs are set, diagnose them first.

2. Ignition ON, observe the scan tool Driver Shift Control parameter. Move the automatic shift lever through all of the positions. The reading should display Active in the manual mode (M) position and, Inactive in all other positions.
3. After performing the above steps, verify that the DTC does not reset by operating the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions you observe from the Freeze Frame/Failure Records data. If the vehicle passes the Circuit/System Verification procedure, then STOP. Do not perform the Circuit/System Testing or Component Testing as this may result in an unnecessary part replacement. Refer to Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the transmission shift lever.
2. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 1 and ground.

• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

3. Verify the scan tool Driver Shift Request parameter indicates Invalid.

• If other than the specified value, test the Tap Up/Tap down signal circuit for a short to voltage. If the circuit tests normal, replace the control solenoid valve assembly.

4. Ignition OFF, test for 8.0-8.5 K ohm between the automatic transmission shift lever connector terminals 1 and 2. Verify the resistance changes to 2.7-3.1 K ohm when the Tap Up switch is pressed and 1.1-1.5 K ohm when the Tap Down switch is pressed.

• If not the specified value, test the circuits between the automatic shift lever assembly connector and shift lever knob connector for a short or an open/high resistance. If the circuits test normal, replace the automatic transmission shift lever knob.

5. Test the Tap Up/Tap Down signal circuit for an open/high resistance or short to ground.

• If circuit tests normal, replace the control solenoid valve assembly.

Repair Instructions

Note:
* Perform the Reset Transmission Adapts Programming and Relearning following all transmission related repairs.
* Before replacing the TCM, perform the Control Solenoid Valve and Transmission Control Module Assembly Inspection Component Tests and General Diagnostics.

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Transmission Control Replacement Transmission Control Replacement for AT TAP shift switch replacement.
* Control Module References Control Module References for body control module (BCM) or control solenoid valve assembly replacement, setup, and programming