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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2009 🢒 Sierra Denali 🢒 Transmission 🢒 Automatic Transmission - Allison 🢒 DTC P0708

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 Descriptor

DTC P0708: Transmission Range Switch Circuit High Voltage

Typical Scan Tool Data

IMS Switch

Display Parameters

Normal Range

Short to Ground

Open/High Resistance

Operating Conditions: Ignition ON, engine OFF, transmission in park position

TR Sw. A/B/C/P (A)

Off

Off

On

TR Sw. A/B/C/P (B)

On

Off

On

TR Sw. A/B/C/P (C)

On

Off

On

TR Sw. A/B/C/P (P)

Off

Off

On

Operating Conditions: Ignition ON, engine OFF, transmission in drive position

TR Sw. A/B/C/P (A)

On

Off

On

TR Sw. A/B/C/P (B)

Off

Off

On

TR Sw. A/B/C/P (C)

Off

Off

On

TR Sw. A/B/C/P (P)

On

Off

On

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 greater than 9.0 V and less than 18 V.
    • Engine speed is greater than 200 RPM and less than 7500 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
    • The TCM requests the ECM to illuminate the malfunction indicator lamp (MIL).
    • If the selector is moved to forward, 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 overspeeding or direction change, then the transmission will shift to NEUTRAL.
    • The TCM freezes shift adapts.
    • DTC P0708 is stored in TCM history.
    • 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

Connector End View Reference

Component Connector End Views

Description and Operation

    •  Transmission General Description
    •  Transmission Component and System Description
    •  Electronic Component Description

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

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.
  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.
  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.
    3. ⇒If not the specified value, test the affected IMS signal circuit for a short to ground. If the circuit tests normal, replace the TCM.
    2.1. Connect a 3A fused jumper wire to the IMS A signal circuit terminal V to low reference circuit terminal H
    2.2. IMS B signal circuit terminal U to low reference circuit terminal H
    2.3. IMS C signal circuit terminal T to low reference circuit terminal H
    2.4. IMS P signal circuit terminal W to low reference circuit terminal H
    2.5. Verify with a scan tool that the TR Sw. A/B/C/P parameters changed from On to Off
    ⇒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.
  3. Remove the transmission oil pan and transmission internal filter. Refer to Oil Pan Replacement.
  4. Test the internal wiring harness IMS signal circuits for open/high resistance and short to ground.
    5. ⇒If circuits test normal, replace the IMS. Refer to Transmission Internal Mode Switch Replacement.
  5. Replace the internal wiring harness. Refer to Wiring Harness Replacement.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Transmission Internal Mode Switch Replacement
    •  Wiring Harness Replacement
    •  Control Module References for TCM replacement, setup, and programming
    •  FastLearn Procedure

Repair Verification

If another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.