P1877

DTC P1876 or P1877

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 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.


If the transmission control module (TCM) detects TAP enable switch Active and the TR switch does not indicate D3, DTC P1876 sets. DTC P1876 is a type C DTC.


If the TCM detects TAP enable switch Inactive and the TR switch indicates D3, DTC P1877 sets. DTC P1877 is a Type C DTC.


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 5 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 5 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 (LE5) (Electrical Diagrams)Automatic Transmission Controls Schematics (LZ4) (Electrical Diagrams)
Connector End View Reference

Component Connector End Views
Description and Operation

TAP Shift Operation (TAP Shift Operation)
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 Testing

1. 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 terminal D at the automatic transmission shift lock 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.

2. While observing the Driver Shift Control parameter on the scan tool place the shifter in D3. The Driver Shift Control parameter should display Active.

• If the Driver Shift Control parameter does not indicate Active, test the ground circuit terminal G at the automatic transmission shift lock control assembly for an open circuit.

3. 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

Test the Tap Up/Tap Down signal circuit of the floor shift control 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 TCM.



Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

* Transmission Control Replacement (Transmission Control Replacement)
* Control Module References for TCM replacement, setup, and programming.