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 VoltageDTC P1877: Up and Down Shift Enable Switch Circuit High Voltage
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Tap Up/Tap Down Switch Signal | P1876 | P1876 | P1877 | -- |
Typical Scan Tool Data
Circuit | Short to Ground | Open/High Resistance | Short to Voltage |
|---|---|---|---|
Operating Conditions: Turn ON the ignition, with the engine OFF Parameter Normal Range: Driver Shift Request - Upshift, Downshift, Invalid, or None Driver Shift Control - Active, or Inactive | |||
Driver Shift Control | Inactive | Inactive | Inactive |
Driver Shift Request | None | Invalid | Invalid |
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
Connector End View Reference
Description and Operation
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Ignition ON, transmission in Park, observe the scan Driver Shift Control parameter. The parameter should display Inactive.
- Shift the transmission into M, the parameter should display Active.
- 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
- Ignition OFF. Disconnect the automatic transmission control assembly connector.
- Ignition ON, verify that a test lamp illuminates between the 12-volt reference circuit terminal 2 and ground.
- Ignition OFF, test for 300-500 ohms between the Tap Up/ Tap Down enable signal circuit and ground.
- If all circuits test normal test or replace the automatic transmission control assembly.
| ⇒ | 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. |
| ⇒ | 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. |
Component Testing
- Ignition OFF, disconnect the automatic transmission control assembly connector.
- 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 after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup, and programming. |
