GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2008 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC P0079 or P0080

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 P0079: Exhaust Throttle Control Valve Circuit Low Voltage

DTC P0080: Exhaust Throttle Control Valve Circuit High Voltage

Diagnostic Fault Information

Circuit

Short to Ground

Open

Short to Voltage

Exhaust Brake and Exhaust Throttle Solenoid Control

P0079

P0079

P0079

Circuit/System Description

The exhaust throttle solenoid is installed to the frame near the exhaust throttle valve of exhaust pipe. When the DPF regeneration mode is ON, the exhaust brake is ON , then the exhaust throttle solenoid is turned ON by the engine control module (ECM).

Conditions for Running the DTC

P0079

    • DTC P0080 is not set.
    • The ignition is ON for longer than 2 seconds.
    • The battery voltage is between 10-16 volts.
    • The exhaust throttle command is OFF.

P0080

    • DTC P0079 is not set.
    • The battery voltage is between 10-16 volts.
    • The ignition is ON for longer than 2 seconds.
    • The exhaust throttle command is OFF.

Conditions for Setting the DTC

P0079

    • The solenoid control monitor level is high.
    • The exhaust brake is commanded OFF.

P0080

    • The solenoid control monitor level is low.
    • The exhaust brake is commanded ON.

Action Taken When the DTC Sets
    • DTCs P0079 and P0080 are Type A DTCs.
    • The malfunction indicator lamp (MIL) is illuminated.
    • The ECM records Freeze Frame data.

Conditions for Clearing the DTC
    • DTCs P0079 and P0080 are Type A DTCs.
    • The ECM turns OFF the MIL after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

Inspect for any recent engine exhaust mechanical repairs. An incorrectly installed exhaust throttle solenoid will cause this DTC to set.

Reference Information

Schematic Reference

Engine 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

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Verify the integrity of the engine exhaust system by inspecting for the following conditions:

    • Damaged components
    • Loose or improper installation

Circuit/System Testing

Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

  1. Ignition OFF, disconnect the harness connector at the exhaust throttle solenoid.
  2. Ignition ON, verify that a test lamp illuminates between the power supply circuit and ground.
    3. ⇒If the test lamp does not illuminate, test the power supply circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, disconnect the harness connector at the ECM.
  4. Install a 3-amp fused jumper wire between the power supply circuit and the control circuit at the exhaust throttle solenoid.
  5. Ignition ON, verify that a test lamp illuminates between the control circuit at ECM and ground.
    6. ⇒If the test lamp does not illuminate, test the power supply circuit for a short to ground or an open/high resistance.
  6. Ignition OFF, test for between 15-20 ohms at solenoid terminals.
    7. ⇒If resistance is not within 15-20 ohms, replace the solenoid. If the solenoid tests normal, replace the ECM.
  7. Inspect the exhaust throttle.
    8. ⇒If an abnormal condition is detected, remove the exhaust throttle.

Component Testing
    • With the ignition ON, command the exhaust brake and the exhaust throttle control solenoid ON and OFF with a scan tool.
    • The test lamp should change from Bright to Dim when commanded ON and OFF.
       ⇒If the test lamp does NOT change brightness, test the high control and low control circuits for an open, high resistance, short to ground, and the low control circuit for a short to voltage. If the circuits test normal, replace the ECM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Exhaust Throttle Replacement
    •  Control Module References for ECM replacement, setup, and programming