GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2009 🢒 Tahoe - 2WD 🢒 Transmission 🢒 Automatic Transmission - 2ML70 🢒 DTC P079B

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 P079B: Transmission Friction Element 2 Slip Detected

Typical Scan Tool Data

Hybrid Direct, 2-3-4 Clutch Reference

Parameter

Commanded ON

Commanded OFF

Slipping when Commanded ON

Operating Conditions: Vehicle speed 0-80 km/h (0-50 mph)

Parameter Normal Range: 0-6,000 RPM

Clutch 2 Slip Speed

0 RPM

0-6,000 RPM

0-6,000 RPM

Clutch 2 Status

Applied

Released

Applied

Circuit/System Description

The transmission control module (TCM) monitors Clutch 2 Slip Speed for each Hybrid Trans. Mode Commanded state. This DTC detects clutch slip when the hybrid direct, 2-3-4 clutch is commanded ON.

Conditions for Running the DTC
    • Hybrid direct, 2-3-4 clutch is the primary on-coming clutch.
    • The clutch PC solenoid 3 commanded pressure is 1800 kpa (261 psi) for 3 seconds.

Conditions for Setting the DTC

The TCM detects the hybrid direct, 2-3-4 clutch slip is greater than 200 RPM for greater than 3 seconds.

Action Taken When the DTC Sets
    • P079B is a Type B DTC.
    • The TCM inhibits gear 2, gear 3, gear 4 and EVT high.

Conditions for Clearing the DTC

P079B is a Type B DTC.

Diagnostic Aids

When attempting to set transmission performance DTCs, observe the Freeze Frame and Failure Records to assist in duplicating the failure conditions. Ensure the transmission fluid level is correct and there are no leaks. If there are any other transmission DTCs set, diagnose those first.

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

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Circuit/System Verification
  1. Verify that DTCs P0721, P0722, P0723, P0966, P0967, P0969, P0970, P0971, P0973, P0974, P0976, P0977, P2720, P2721, P2728, P2729, or P2730 are not set.
    2. ⇒ If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.
  2. Clear the DTC.
  3. Operate the vehicle from 1st through 4th gear while observing the Clutch 2 Slip Speed parameter. Stop the vehicle and turn the ignition OFF for 30 seconds. Perform this action 2 times. The Clutch 2 Slip Speed parameter should display 0 RPM when the Clutch 2 Status parameter displays Applied.
    4. ⇒If any other transmission DTCs are set, diagnose those first.
    ⇒If DTC P079B resets, go to Component Testing.

Component Testing
  1. Perform the Line Pressure Check.
  2. Perform the Control Solenoid Valve and Transmission Control Module Assembly Solenoid Performance Test.
    3. ⇒If a concern is found, replace the control solenoid (w/body and TCM) valve assembly.
  3. Inspect the trans fluid pump ball check valve for possible sticking or damage.
    4. ⇒If you found a concern with this check ball, repair the concern.
  4. Inspect the hybrid direct, 2-3-4 clutch regulator valve for sticking or damage.
    5. ⇒If you found a concern with the hybrid direct, 2-3-4 clutch regulator valve, repair or replace the valve or valve body.
  5. Inspect the hybrid direct, 2-3-4 clutch for a slipping or damaged condition.
    6. ⇒If you found a hybrid direct, 2-3-4 clutch concern, repair or replace the hybrid direct, 2-3-4 clutch assembly as necessary.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Control Module References for control solenoid (w/body and TCM) valve assembly replacement, setup, and programming.
    •  Hybrid Direct, 2-3-4 Clutch Housing Overhaul for hybrid direct, 2-3-4 clutch replacement.
    •  Control Solenoid Valve and Transmission Control Module Assembly Replacement for lower valve body assembly replacement.
    •  Control Valve Assembly Disassemble and Control Valve Assembly Assemble for valve body inspection procedures. If the inspection procedure indicates to replace the valve body, refer to Control Solenoid Valve and Transmission Control Module Assembly Replacement.