GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2009 🢒 Chevy Suburban - 2WD 🢒 DTC 🢒 DTC P1684-P1686

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 P1684:  Transmission Control Module (TCM) Power Up Temperature Sensor Performance

DTC P1685:  Transmission Control Module (TCM) Power Up Temperature Sensor Circuit Low Voltage

DTC P1686:  Transmission Control Module (TCM) Power Up Temperature Sensor Circuit High Voltage

Circuit/System Description

The transmission control module (TCM) power up temperature sensor is located inside of the control solenoid (w/body and TCM) valve assembly and has no serviceable parts. The TCM power up temperature sensor provides the temperature of the TCM at TCM power up. This temperature reading is used in various shifting and diagnostic routines in the TCM software. This fault is handled inside the TCM and no external circuits are involved.

Conditions for Running the DTC

The engine speed is greater than 450 RPM.

P1684

    • No DTCs P0711, P0712, P0713, P0716, P0717, P0722, P0723, or P1684.
    • DTC P1684 has not passed this key ON.
    • The TCM power up temperature is between -39 and +149°C (-38 and +300°F).

P1685

    • No DTCs P0716, P0717, P0722, or P0723.
    • The transmission output shaft speed is greater than 200 RPM for greater than 200 seconds.
    • The torque converter clutch (TCC) slip speed is equal to or greater than 120 RPM for 200 seconds or greater.
    • DTC P1685 has not failed this ignition cycle.

P1686

DTC P1686 has not failed this ignition cycle.

Conditions for Setting the DTC

P1684 - Fail Case 1

    • Vehicle speed is greater than 8 km/h (5 mph) for 300 seconds cumulative.
    • TCC slip speed is greater than 120 RPM for 300 seconds cumulative.
    • The TCM power up temperature is between -40 and +21°C (-40 and +70°F).
    • The TCM power up temperature has changed by less than 2°C (3.6°F) in 100 seconds.
    • The transmission fluid temperature (TFT) is greater than 70°C (158°F).
    • The TFT has increased by 55°C (99°F) since startup.

P1684 - Fail Case 2

    • Vehicle speed is greater than 8 km/h (5 mph) for 300 seconds cumulative.
    • TCC slip speed is greater than 120 RPM for 300 seconds cumulative.
    • The TCM temperature sensor is between 120-150°C (248-302°F).
    • The TCM power up temperature has changed by less than 2°C (3.6°F) in 100 seconds.
    • The TFT is greater than 70°C (158°F).
    • The TFT has increased by 55°C (99°F) since startup.

P1684 - Fail Case 3

The TCM power up temperature changes by greater than or equal to 20°C (36°F) 14 times over 7 seconds.

P1685

The TCM power up temperature is less than or equal to -61°C (-77°F) for greater than 10 seconds.

P1686

The TCM power up temperature is greater than or equal to 161°C (321°F) for greater than 10 seconds.

Action Taken When the DTC Sets
    • DTCs P1684, P1685, and P1686 are Type C DTCs.
    • The TCM allows the vehicle to operate in transmission protection mode.

Conditions for Clearing the DTC

DTCs P1684, P1685, and P1686 are Type C DTCs.

Diagnostic Aids

Reprogram the TCM and retest the DTC to see if the DTC resets.

Reference Information

Schematic Reference

Automatic Transmission Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

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

Description and Operation

Electronic Component Description

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification
  1. Start the engine for 1 minute and observe the TCM power up temperature sensor and the TCM temperature sensor.
  2. The system is operating normally if the TCM power up temperature is within 10°C (18°F) of the TCM temperature sensor.

Circuit/System Testing
  1. Clear the DTC and operate the vehicle under the condition for running and setting the DTC.
  2. Shut the ignition OFF for 30 seconds, and verify that the DTC does not reset.
    3. ⇒If the DTC resets, replace the control solenoid (w/body and TCM) valve assembly.

Component Testing

Perform the Control Solenoid Valve and Transmission Control Module Assembly Inspection .

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    • Control solenoid (w/body and TCM) valve assembly replacement. Refer to Control Module References for replacement, setup, and programming.
    • Perform the Service Fast Learn Adapts if internal transmission repairs are performed.