P1877

DTC P1876 or P1877

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.

DTC Descriptors
DTC P1876
- Up and Down Shift Enable Switch Circuit Low Voltage

DTC P1877
- Up and Down Shift Enable Switch Circuit High Voltage

Diagnostic Fault Information





Typical Scan Tool Data





Circuit/System Description

The 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. The TAP shift system is activated when the gear selector is in the D3 position and is deactivated in all other positions.

Conditions for Running the DTC

P1876
* To TR switch DTC P0705.
* No TAP system DTCs P0815, P0816, or P0826.
* No TFP DTCs P1810, P1816, or P1818.
* No DTC P1877.
* No Communication DTC U0100.
* The engine speed is greater than 500 RPM for 2 seconds.
* The ignition is ON.

P1877
* To TR switch DTC P0705.
* No TAP system DTCs P0815, P0816, or P0826.
* No TFP DTCs P1810, P1816, or P1818.
* No DTC P1876.
* No Communication DTC U0100.
* The engine speed is greater than 500 RPM for 2 seconds.
* The ignition is ON.

Conditions for Setting the DTC

P1876

The Tap Up/Tap Down switch signal is Active when the TR switch does not indicate D3 for 4 seconds five times during the same trip.

P1877

The Tap Up/Tap Sown switch signal is Inactive when the TR switch does not indicate D3 for 60 seconds during the same ignition cycle.

Action Taken When the DTC Sets

* DTCs P1876 and P1877 are Type C DTCs.
* The TCM disables Tap shift functions.
* The TCM commands an alternate coast shift pattern where downshifts occur at higher vehicle speeds while coasting.

Conditions for Clearing the DIC/DTC

DTCs P1876 and P1877 are Type C DTCs.

Diagnostic Aids

If there are any TFP DTCs, then diagnose them first.

Reference Information
Schematic Reference

Automatic Transmission Controls Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

TAP Shift Operation (TAP Shift Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

DTC Type Reference

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

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

1. Ignition ON, transmission in Park, observe the scan Driver Shift Control parameter. The parameter should display Inactive.
2. Shift the transmission into M, the parameter should display Active.
3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Ignition OFF. Disconnect the automatic transmission control assembly connector.
2. Ignition ON, verify that a test lamp illuminates between the 12-volt reference circuit terminal 2 and ground.

• If the test lamp does not illuminate, test the 12-volt reference circuit for a short to ground or an open/high resistance. If the circuit test normal, replace the BCM.

3. Ignition OFF, test for 300-500 ohms between the Tap Up/ Tap Down enable signal circuit and ground.

• If not within the specified range, test the Tap Up/ Tap Down enable signal circuit for a short to ground or an open/high resistance. If the circuit tests normal replace the BCM.

4. If all circuits test normal test or replace the automatic transmission control assembly.

Component Testing

1. Ignition OFF, disconnect the automatic transmission control assembly connector.
2. Test for 6-8K ohms between the Tap Up/Tap Down enable signal circuit terminal 6 and the 12-volt reference circuit terminal 2.

If not within the specified range, replace the automatic transmission control assembly.

Repair Instructions

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

* Transmission Control Replacement (Transmission Control Replacement)
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming.