6T30/6T40/6T45 - Automatic Transmission

DTC P1876

Diagnostic Instructions

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

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

Circuit/System Description

When the shift lever is placed in manual mode (M), the driver shift request (DSR), also known as the tap shift function is activated. The DSR allows the vehicle operator to shift gears by pushing the shift lever forward for an upshift or pulling the shift lever rearward for a downshift. The body control module (BCM) supplies battery voltage, ground and a signal circuit to the shift controller. The shift controller has Hall-effect switches connected to a resistor array. When the lever is in the M position, then pushed forward for an upshift, or pulled rearward for a downshift, a corresponding voltage drop occurs across the resistor network. This voltage drop is monitored by the BCM. The BCM will send the request to the transmission control module to perform the upshift or downshift.

Conditions for Running the DTC

* The engine speed is greater than 500 RPM for 5 seconds.
* The ignition voltage is greater than 9.0 volts.
* No DTCs P0815, P0816, P0826, P1761, P1825, P1877, P1915, or U0100.

Conditions for Setting the DTC

The transmission control module (TCM) detects a transmission adaptive pressure (TAP) Enable Switch request for 3 seconds when not in D6 range a total of 5 times.

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.

Reference Information
Schematic Reference

Automatic Transmission Controls Schematics (Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

* Transmission General Description (Transmission General Description)
* Electronic Component Description (Electronic Component Description)

Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing For Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

DTC Type Reference

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

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

Circuit/System Verification

1. Verify there are no internal mode switch (IMS) DTCs set.

• If IMS DTCs are set, diagnose them first.

2. Ignition ON, observe the scan tool Driver Shift Control parameter in park, reverse, and neutral. The reading should display Inactive.
3. 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.

Circuit/System Testing

1. Ignition ON, verify the scan tool IMS A/B/C/P parameter matches the Transmission Internal Mode Switch Logic (Transmission Internal Mode Switch Logic) in park, reverse, neutral and drive.

• If not the expected results, refer to Shift Indicator Indicates Wrong Gear Selection (Shift Indicator Indicates Wrong Gear Selection).

2. Ignition OFF, disconnect the shift lever assembly electrical connector from the shift lever assembly.
3. Test for less than 10 ohms between the shift lever harness connector terminal 2 and ground.

• If greater than the specified range, repair the ground circuit.

4. Ignition ON, verify the scan tool Driver Shift Control parameter displays inactive.

• If not the expected results, test the signal circuit between shift lever assembly connector terminal 3 and the BCM for a short to voltage or ground. If the circuit tests normal, replace the BCM.

5. Ignition OFF, connect a test lamp between shift lever harness connector B+ circuit terminal 1 and ground circuit terminal 2.
6. Ignition ON, verify the test lamp is illuminated.

• If the light stays off, test the B+ circuit for an open/high resistance. If the circuit tests normal, replace the BCM.

7. Test for 11-13 volts at the shift lever assembly harness connector between signal circuit terminal 3 and ground.

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

8. Ignition OFF, connect the shift lever harness connector.
9. Ignition ON, back probe the shift lever assembly connector and test for 11-13 volts between terminal 3 and ground with the shift lever in park, reverse, and neutral.

• If not within the specified range, replace the shift lever assembly.

Repair Instructions

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

Note:
* Perform the Transmission Adaptive Values Learn (6T30/6T40/6T45 - Automatic Transmission) following all transmission related repairs.
* Before replacing the TCM, perform the Control Solenoid Valve and Transmission Control Module Assembly Inspection (Control Solenoid Valve and Transmission Control Module Assembly Inspection).

* Transmission Control Replacement (Transmission Control Replacement)for AT TAP shift switch replacement.
* Control Module References (Programming and Relearning)for BCM or control solenoid valve assembly replacement, setup, and programming