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6T30/6T40/6T45/6T50 - 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 plus (+) button for an upshift or minus (-) button 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, a voltage drop occurs across the resistor network. When the plus or minus button is pushed, 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 (TCM) to perform the upshift or downshift.

Conditions for Running the DTC

* The engine speed is greater than 400 RPM for 5 seconds.
* The ignition voltage is 9.0 volts or greater.
* DTC P0815, P0816, P0826, P1761, P1825, P1876, P1877, P1915, or U0100 is not set.

Conditions for Setting the DTC

The transmission control module (TCM) detects a TAP Enable Switch request for 3 seconds when the shift lever is in Park, Reverse, or Neutral, a total of 5 times.

Action Taken When the DTC Sets

* DTC P1876 is a Type C DTC.
* The TCM inhibits Tap-Up/Tap-Down functions.
* The TCM inhibits manual up, manual down shifts with the shift selector.

Conditions for Clearing the DIC/DTC

DTC P1876 is a Type C DTC.

Reference Information
Schematic Reference

Automatic Transmission Controls Schematics (6T30/6T40/6T45/6T50 - Automatic Transmission)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
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 IMS DTCs set.

• If IMS DTCs are set, diagnose them first.

2. Ignition ON, observe the scan tool Driver Shift Control Mode parameter while moving the transmission shift lever through all the positions. The parameter should display Inactive in the park, reverse, neutral, and drive positions, and Active in the M position.
3. Shift lever in the M position, verify the scan tool Driver Shift Request parameter changes from None to Upshift when the plus button is pressed, and from None to Downshift when the minus button is pressed.
4. After performing the above steps, verify that the DTC does not reset by operating the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions you observe from the Freeze Frame/Failure Records data. If the vehicle passes the Circuit/System Verification procedure, then STOP. Do not perform the Circuit/System Testing or Component Testing as this may result in an unnecessary part replacement. Refer to Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections).

Circuit/System Testing

1. Ignition OFF, disconnect the S3 shift lever assembly electrical connector from the S3 shift lever assembly.
2. Test for less than 10 ohms between the S3 shift lever assembly harness connector terminal 2 and ground.

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

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

• If not the expected results, test the signal circuit between S3 shift lever assembly connector terminal 3 and the K9 BCM for a short to voltage or ground. If the circuit tests normal, replace the K9 BCM.

4. Ignition OFF, connect a test lamp between the S3 shift lever assembly harness connector ignition circuit terminal 1 and ground circuit terminal 2.
5. Ignition ON, verify the test lamp is illuminated.

• If the light stays off, test the ignition circuit for an open/high resistance. If the circuit tests normal, replace the K9 BCM.

6. Test for 11-13 volts at the S3 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 K9 BCM.

7. Ignition OFF, connect the S3 shift lever assembly harness connector.
8. Ignition ON, back probe the S3 shift lever assembly connector and test for 11-13 volts between terminal 3 and ground with the shift lever in park, reverse, neutral, and drive.

• If not within the specified range, replace the S3 shift lever assembly.

9. Use a DMM to monitor the voltage between the S3 shift lever assembly connector terminal 3 and ground with the shift lever in the M position, M position with the tap up plus button depressed, and the M position with the tap down minus button depressed. Compare the readings and verify the voltages are correct for each position as follows:

* Manual: 8.0-10.6 volts
* Tap down: 5.1-7.3 volts
* Tap up: 2.0-4.6 volts

• If not within the specified range, test the signal circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the S3 shift lever assembly.

10. If all circuits test normal, replace the K9 BCM.

Repair Instructions

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

Note:
* Perform the Transmission Adaptive Values Learn (6T30/6T40/6T45/6T50 - 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

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