GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2007 🢒 Cobalt 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 DTC P0068 or P0121

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 P0068: Throttle Body Airflow Performance

DTC P0121: Throttle Position (TP) Sensor 1 Performance

Circuit/System Description

The engine control module (ECM) uses the following information to calculate an expected airflow rate:

    • The throttle position (TP)
    • The barometric pressure (BARO)
    • The manifold absolute pressure (MAP)
    • The intake air temperature (IAT)
    • The engine RPM
    • The mass air flow (MAF)

Conditions for Running the DTC
    • DTCs P0641, P0651, P1516, P2101, P2119, P2176 are not set.
    • The engine is running and the engine speed is more than 600 RPM.
    • DTC P0068 and P0121 run continuously when the above conditions are met.

Conditions for Setting the DTC

The ECM detects that the airflow rate is more than the calculated airflow for more than 0.2 second.

Action Taken When the DTC Sets
    • DTC P0068 is a Type A DTC.
    • DTC P0121 is a Type B DTC.
    • The control module commands the throttle actuator control (TAC) system to operate in the Reduced Engine Power mode.
    • A message center or an indicator displays Reduced Engine Power.
    • Under certain conditions the control module commands the engine OFF.

Conditions for Clearing the MIL/DTC
    • DTC P0068 is a Type A DTC.
    • DTC P0121 is a Type B DTC.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Controls Connector End Views
    •  Engine Control Module Connector End Views

Description and Operation

Throttle Actuator Control (TAC) System 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

    •  Scan Tool Data List
    •  Scan Tool Data Definitions

Circuit/System Testing
  1. Inspect for the following conditions:
    2. • Vacuum hoses for splits, kinks, and proper connections as shown on Vehicle Emission Control Information label
    • Inspect thoroughly for any type of leak or restriction.
    • Air leaks at throttle body mounting area and intake manifold sealing surfaces
    • Inspect throttle body for dirt debris. Refer to Throttle Body Cleaning .
  2. Allow the engine to reach operating temperature. Observe the Manifold Absolute Pressure (MAP) Sensor Voltage parameter with a scan tool. Voltage should be more than 0.8 volt and less than 4 volts.
    3. ⇒If more than 4 volts or less than 0.8 volt, refer to DTC P0106 .
  3. Idle the engine. Observe the MAP Sensor kPa parameter with a scan tool. Increase the engine speed slowly and then back to idle. The MAP sensor kPa should change smoothly and gradually as engine speed is increased and returned to idle.
    4. ⇒If the MAP sensor kPa does not change refer to DTC P0106 .
  4. Take a snapshot of the engine data list while performing the actions listed below. The MAF sensor kPa should change smoothly and gradually as the engine speed is increased and is returned to idle.
    5. • Idle the engine.
    • Increase the engine speed slowly to 3,000 RPM, then back to idle.
    • Exit from the snapshot and review the data.
    • Observe the Mass Air Flow (MAF) Sensor parameter frame by frame with a scan tool. The MAF sensor g/s should change smoothly and gradually as the engine speed is increased and is returned to idle .
         ⇒If the MAF sensor g/s does not change smoothly and gradually as the engine speed is increased and is returned to idle refer to DTC P0101 or P1101 .
  5. Inspect the throttle body for the following conditions:
    6. • Loose or damaged throttle blade
    • Broken throttle shaft
    • Any throttle body damage
    ⇒If any of these conditions exist, replace the throttle body assembly.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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