M99 - Automatic Transmission

DTC P0815, P0816, or P0826

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 P0815
- Upshift Switch Circuit

DTC P0816
- Downshift Switch Circuit

DTC P0826
- Up and Down Shift Switch Circuit




Diagnostic Fault Information






Circuit/System Description

The driver shift control (DSC), also known as the TAP Shift, allows the driver to manually shift transmission modes and gears by pressing the Plus/Minus button and select the desired range of gears for your current driving conditions by using the DSC shift switch located on the automatic transmission gear shift lever. Pushing the Plus switch will command an upshift and pushing the Minus switch will command a downshift. 12 volt reference voltage flows from the ignition body control module (BCM) through the DSC switch resistor array to the BCM. The DSC shift system is activated when the gear selector is in the Manual (M) position. DSC system is deactivated in all other range positions.


Conditions for Running the DTC

The engine speed is between 500-6,500 RPM for at least 5 seconds.


P0815 or P0816
* No DTC P0826.
* No DTCs P1815 or P1826.
* The time since the last gear selector range change is greater than 6 seconds.



Conditions for Setting the DTC

P0815

The BCM detects an upshift request for 3 seconds when the transmission range selector is in P, R, N, or D and for 600 seconds in P, R, NEUTRAL.

P0816

The BCM detects a downshift request for 3 seconds in P, R, N, or D and for 600 seconds in P, R, N, D.

P0826

The BCM detects an invalid voltage on the TAP up/down signal circuit for 5 seconds.


Action Taken When the DTC Sets

* DTCs P0815, P0816, and P0826 are Type C DTCs.
* The BCM disables TAP shift operation.



Conditions for Clearing the DTC

DTCs P0815, P0816, and P0826 are Type B DTCs.


Reference Information
Schematic Reference

Automatic Transmission Controls Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views
Electrical Information Reference

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

DTC Type Reference

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

* Scan Tool Output Controls (Scan Tool Output Controls)
* Scan Tool Data List (Scan Tool Data List)
* Scan Tool Data Definitions (Scan Tool Data Definitions)



Circuit/System Verification

P0815, P0816, or P0826

With the engine ON, engage the DSC Plus/Minus switch positions while observing the Driver Shift Request parameter in the body controls scan tool data list. The parameter should change to reflect the selected Up or Downshift switch position and with no Up or Downshift switch position selected the parameter should display None.


Circuit/System Testing


P0815
1. Select the Driver Shift Request parameter.
2. Disconnect the automatic transmission DSC shift switch connector.

• If the parameter status changes from Upshift to Invalid, replace the DSC shift switch.


• If the parameter status does not change, replace the BCM.




P0816
1. Select the Driver Shift Request parameter.
2. Disconnect the DSC shift switch connector.

• If the parameter status changes from Downshift to Invalid, replace the DSC shift switch.


• If the parameter status does not change, replace the BCM.




P0826
1. Test the 12 volt reference circuit and the tap up and tap down switch signal circuit for a short to ground.

• If the circuits test OK, test the 12 volt reference circuit and the tap up and tap down signal circuit for an open or short to voltage.

2. Test the DSC shift switch for correct resistance value, 8.11-8.39 ohms.

• If the resistance is not within specifications, replace the switch assembly.


• If the resistance is within specifications, replace the BCM.




Component Testing

Test the DSC shift switch for correct resistance value, 8.11-8.39 ohms.

If the resistance is not within specifications, replace the DSC switch.



Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

* Replace the DSC shift switch. Refer to Shift Lever Replacement (Shift Lever Replacement) .
* Replace the BCM. Refer to Control Module References for replacement, setup, and programming.