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 VoltageDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Tap Up/Tap Down Switch Signal | P1876 | P1876 | -- | -- |
Typical Scan Tool Data
Circuit | Normal Range | Short to Ground | Open/High Resistance | Short to Voltage |
|---|---|---|---|---|
Driver Shift Control | Inactive | Inactive | Inactive | Active |
Driver Shift Request | None | Invalid | 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 L position and is deactivated in all other positions.
If the transmission control module (TCM) detects TAP enable switch Active and the IMS switch does not indicate L, DTC P1876 sets. DTC P1876 is a type C DTC.
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. |
Conditions for Setting the DTC
The Tap Up/Tap Down switch signal is Active when the IMS does not indicate L 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.
Diagnostic Aids
If there are any IMS DTCs, then diagnose them first.
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics
Connector End View Reference
Electrical Information Reference
Scan Tool Reference
DTC Type Reference
Description and Operation
Electronic Component Description
Circuit/System Testing
- Check to see if any IMS DTCs are set.
- 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 at the automatic transmission control assembly connector. The voltage should be near battery voltage.
- While observing the Driver Shift Control parameter on the scan tool place the shifter in L. The Driver Shift Control parameter should display Active.
- 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 IMS DTCs are set, diagnose them first. |
| ⇒ | If the voltage is not near battery voltage, test the Tap Up/Tap Down enable switch circuit for an open. |
| ⇒ | If the Driver Shift Control parameter does not indicate Active, test the ground circuit at the automatic transmission control assembly for an open circuit. |
| ⇒ | If any of the conditions are not found, test the automatic transmission control assembly. |
Component Testing
Disconnect the automatic transmission control assembly connector. Place the automatic transmission control assembly in L. Measure the resistance between the Tap Up/Tap Down enable signal circuit and the ground circuit of the automatic transmission control assembly. The resistance should be less than 1 ohm.
| ⇒ | If the resistance is greater than 1 ohm, replace the automatic transmission control assembly. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
