P0708
DTC P0708
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 P0708
- Transmission Range Switch Circuit High Voltage
Typical Scan Tool Data
Circuit/System Description
The internal mode switch (IMS) consists of 5 internal switches, A, B, C, P and Neutral Start (NS). The IMS is attached to the selector shaft, and the switches change state depending on the position of the selector shaft. The TCM uses four of the internal switches, A, B, C, and P, to determine the gear range that is selected. The ECM uses the NS switch as confirmation that the transmission is in neutral or park before the engine starter is engaged.
Conditions for Running the DTC
* Ignition voltage is between 9-18 V.
* Engine speed is greater than 200 RPM for 5 seconds.
Conditions for Setting the DTC
Condition 1
This DTC sets when an illegal range is detected for greater than 1 second.
Condition 2
This DTC sets after a number of drive cycles where the TCM detects a logic error on the IMS A, B, C, and P circuits.
Action Taken When the DTC Sets
* DTC P0708 is a Type A DTC.
* If the selector is moved to drive or any other forward position, the transmission will shift to third or fifth range. If the selector is moved to Neutral, the transmission will shift to Neutral. If the selector is moved to reverse, the transmission will shift to reverse unless the transmission is compromised by over-speeding or direction change, then the transmission will shift to NEUTRAL.
* The TCM freezes shift adapts.
* The TCM inhibits torque converter clutch (TCC) engagement.
Conditions for Clearing the DTC
DTC P0708 is a Type A DTC.
Diagnostic Aids
* The scan tool will display On when IMS A, B, C, or P is open, and Off when IMS A, B, C, or P is closed.
* It may take several drive cycles to get this DTC to set.
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. Verify the range selector lever cable adjustment is correct; refer to Range Selector Lever Cable Adjustment (Allison - Automatic Transmission).
2. Ignition ON, engine OFF, move the shift selector lever through all the ranges. With a scan tool, verify the TR Sw. A/B/C/P parameters match the IMS A, B, C, and P circuit states in the transmission IMS logic table. Refer to Transmission Internal Mode Switch Logic (Transmission Internal Mode Switch Logic).
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 OFF, disconnect the X175 harness connector at the transmission.
2. Ignition ON, engine OFF, verify with a scan tool the TR Sw. A/B/C/P parameters are all On.
• If not the specified value, test the affected IMS signal circuit for a short to ground. If the circuit tests normal, replace the TCM.
3. Connect a 3A fused jumper wire between the IMS signal circuit terminals listed below and low reference circuit terminal H. Verify with a scan tool that the TR Sw. A/B/C/P parameters changed from On to Off.
1. IMS signal circuit A terminal V
2. IMS signal circuit B terminal U
3. IMS signal circuit C terminal T
4. IMS signal circuit P terminal W
• If not the specified value, test the affected IMS signal circuits and low reference circuit for an open/high resistance. If the circuits test normal, replace the TCM.
4. Ignition OFF, remove the transmission oil pan and transmission internal filter. Refer to Oil Pan Replacement (Allison - Automatic Transmission).
5. Test the internal wiring harness IMS signal circuits and low reference circuits for an open/high resistance and short to ground.
• If circuits test normal, replace the IMS. Refer to Transmission Internal Mode Switch Replacement (Service and Repair).
6. Replace the internal wiring harness. Refer to Wiring Harness Replacement (Allison - Automatic Transmission).
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Transmission Internal Mode Switch Replacement (Service and Repair)
* Wiring Harness Replacement (Allison - Automatic Transmission)
* Control Module References (Control Module References) for TCM replacement, setup, and programming
* FastLearn Procedure (Allison - Automatic Transmission)
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.