Allison - Automatic Transmission
DTC P0815, P0816, or P0826
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 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 drivers shift request (DSR), also known as the TAP Shift, allows the driver to manually shift gears by pressing the plus (+) or minus (-) buttons and select the desired range of gears for current driving conditions by using the DSR 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. The body control module (BCM) supplies an ignition voltage circuit and signal circuit to the DSR switch resistor array. A voltage drop occurs across the resistor network. When the plus or minus button is pushed, a corresponding change in voltage drop occurs across the resistor network. This voltage drop is monitored by the BCM. The BCM sends the request to the transmission control module to perform the upshift or downshift. The DSR shift system is activated when the gear selector is in the Manual (M) position. The DSR system is deactivated in all other range positions.
Conditions for Running the DTC
P0815 or P0816
* The engine speed is greater than 200 RPM for 5 seconds.
* The ignition voltage is between 9-18 V.
* DTC P0708 or P0826 is not set.
* The time since the last gear selector range change is greater than 3 seconds.
P0826
* The engine speed is greater than 200 RPM for 5 seconds.
* The ignition voltage is between 9-18 V.
* DTC P0826 is not set.
Conditions for Setting the DTC
P0815 Condition 1
The BCM detects an upshift request for 3 seconds in PARK, REVERSE, or NEUTRAL.
P0815 Condition 2
The BCM detects an upshift request for 10 minutes in any forward gear.
P0816 Condition 1
The BCM detects an upshift request for 3 seconds in PARK, REVERSE, or NEUTRAL.
P0816 Condition 2
The BCM detects a downshift request message for 10 minutes in any forward gear.
P0826
The BCM detects an invalid voltage on the TAP up/down signal circuit for 10 seconds.
Action Taken When the DTC Sets
* DTCs P0815, P0816, and P0826 are Type C DTCs.
* TAP shift operation is disabled.
Conditions for Clearing the DTC
DTCs P0815, P0816, and P0826 are Type C DTCs.
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics (Allison - Automatic Transmission)
Connector End View Reference
* Component Connector End Views (Connector End Views By Name)
* Inline Harness Connector End Views (Connector End Views By Number)
Description and Operation
* Transmission General Description (Transmission General Description)
* Transmission Component and System Description (Transmission Component and System 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 (Control Module References) for scan tool information
Circuit/System Verification
1. Ignition ON, Engine OFF, transmission in Park, verify with a scan tool the BCM Tap Up/Down Switch parameter displays On.
2. Shift selector in the Manual (M) position, cycle the automatic transmission manual shift switch while observing the Tap Up/Down Switch parameter. The parameter should change from On to Up when the plus (+) switch is selected, and from On to Down when the minus (-) switch is selected.
3. Operate the vehicle within the Conditions for Running the DTC to verify that the DTC not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Circuit/System Testing
1. Ignition OFF, disconnect the automatic transmission shift lever harness connector.
2. Ignition ON, verify with a scan tool the Tap Up/Down Switch parameter displays Off.
• If not the specified value, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.
3. Test for greater than 11 V between the ignition voltage circuit terminal 4 and ground.
• If less than the specified value, test the ignition voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
4. Ignition OFF, test for 6.6-7.0 K ohms between terminal 3 and terminal 4 of the automatic transmission shift lever harness connector. Also, test for 3.7-4.2 K ohms when pressing the minus (-) switch, and 1.7-2.0 K ohms when pressing the plus (+) switch.
• If not within the specified values, replace the automatic transmission lever.
5. Test the signal circuit between the BCM and the automatic transmission manual shift switch for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Shift Lever Replacement (Shift Lever Replacement) for RSM shift switch replacement.
* Control Module References (Control Module References) for BCM replacement, setup, and programming.
Repair Verification
If another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle) and perform the appropriate diagnostic procedure.