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.
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
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
- Verify there are no TR switch DTCs set.
- Ignition ON, transmission in Park, observe the scan tool Driver Shift Control parameter. The reading should display Inactive.
- Shift the transmission in D3, observe the scan tool Driver Shift Control parameter. The reading should display Active.
- Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
| ⇒ | If TR switch DTCs are set, diagnose them first. |
Circuit/System Testing
- Ignition OFF, disconnect the automatic transmission control assembly connector.
- Ignition ON, test for B+ on the Tap Up/Tap Down enable switch circuit terminal D at the automatic transmission shift lock control assembly harness connector.
- Test for less than 10Ω between the ground circuit terminal G and Ground.
- With the shift lever in park, test for infinite resistance between terminal D and terminal G of the automatic transmission shift lock control assembly.
- With the shift lever in D3, test for less than 10Ω between terminal D and terminal G of the automatic transmission shift lock control assembly.
- If all circuits test normal, replace the BCM.
| ⇒ | If not the specified value, test the Tap Up/Tap Down enable switch circuit for an open/high resistance. If the circuit tests normal, replace the BCM. |
| ⇒ | If not the specified range, test the ground circuit at the automatic transmission shift lock control assembly for an open/high resistance. |
| ⇒ | If not the specified value, replace the automatic transmission shift lock control assembly. |
| ⇒ | If not the specified value, replace the automatic transmission shift lock control assembly. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for TCM replacement, setup, and programming. |
